Biography_Dalton_ENG.pdf Biography: John Dalton 1 Storytelling Teaching Model: wiki.science-stories.org Biography: John Dalton John Dalton (1766 – 1844) was an English physicist and chemist, a teacher in Manchester and a professor at Oxford University. Dalton was a man of diverse interests, although his greatest achievements were in the field of chemistry. Dalton introduced atomic theory by explaining the law of constancy of chemical composition, and formulating the laws of partial pressures and multiple proportions. He also carried out numerous tests on gas absorption in liquids and thermal expansion of gases, and de- scribed the condition known as daltonism. He regularly observed the weather, studied the phenomenon of aurora Polaris and explained what causes the trade winds. John Dalton was born on September 6, 1766 in Eaglesfield, Cumberland, England. He was born to an impoverished family. His father was a weaver and owned a small piece of land. Despite their poor financial situation, John received a good gen- eral education. However, he soon left school and started helping his father. When John was 12, he started working as a teacher in a local school. He earned his living and provided himself with a quiet, untroubled life. Me- teorology was his passion. He constructed barom- eters and other scientific instruments used in this field. He began to keep a diary where he entered his weather observations. During his life he made more than 200,000 observations and published them as a book in 1793. Young Dalton was busy teaching at school, helping his father, and studying Latin, Greek, and natural sciences. After two years he moved to Kendal where he began teaching at the school run by his older brother, Jonathan. After twelve years, he travelled to Manchester, where he was appoint- ed as professor at the Warrington Academy. Dur- ing this time, he devoted every spare moment to conducting physics experiments. In 1781, he began teaching high school math- ematics and in 1793 he became a teacher of math- ematics and natural philosophy at the New Col- lege in Manchester. There he met Robert Owen, who introduced him to the Manchester Literary and Philosophical Society. Soon Dalton became a secretary and since 1817 was the President of the Society. Over a period of 50 years, Dalton present- ed 116 of his scientific works. In addition, Dalton created his private laboratory in the building be- longing to the Manchester Literary and Philosoph- ical Society, where he conducted most of his chemical experiments and weather observations. In 1799, the Society moved out of Manchester, but Dalton remained in the city giving private lessons for two shillings per hour. Dalton was a Quaker. He wore a traditional grey coat, a white scarf on his neck, knee-breeches, grey hose and boots with buckles. In the company of other people he was tense and often felt uncom- fortable. He never succeeded as a lecturer because he lacked charisma. He also never married, claim- ing that he could not afford to have a wife. Dalton had a great interest in weather observa- tions and he began doing research on atmospheric composition. He collected air samples from differ- ent places on Earth and observed that atmospheric composition is the same regardless of the location. Dalton also proved that the atmosphere is not a chemical compound, but instead is a composition of various gases. He stated that the total pressure exerted by the mixture of gases is equal to the sum of the partial pressures of individual gases. This observation later became known as Dalton's law of partial pressures, or simply Dalton's law. This prominent scholar was very curious about one particular aspect of gases. John knew that car- bon dioxide is quite heavy, oxygen is lighter, ni- trogen is even lighter and water vapor is the light- est of the four, being two times lighter than carbon dioxide. Knowing this, Dalton wondered why there was a layer of water vapor above the ground, instead of the layer of carbon dioxide. Dalton tried to imagine the structure of the above mentioned compounds to explain the concept of diffusion. 2 Biography: John Dalton Storytelling Teaching Model: wiki.science-stories.org This was the beginning of his detailed studies, which resulted in the creation of a highly contro- versial theory. In this theory, Dalton stated that everything is made of atoms. Dalton's atomic theory can be described in four main points: 1) All substances are made of atoms. 2) Atoms of the same substance are the same and have the same mass; atoms of different substances differ from each other and have different masses. 3) A chemical reaction involves connection, dividing and exchanging atoms. In other words, the atom is a basic unit involved in a chemical reaction and cannot be subdivid- ed. 4) If two or more compounds made of the same elements exist, the simplest com- pound of all will contain one atom of every element present there. Dalton presented this theory to the Royal Insti- tution in 1803. More precise details were included in the general “System of Chemistry,” which was later written by the chemist Thomas Thomson. Dalton conducted an analysis of two molecules of carbon monoxide and found that in one of them the mass of oxygen is two times bigger than the mass of carbon. He suspected that a rule must exist to explain this phenomenon and conducted an analysis using nitrous oxide. This time, he care- fully examined three gases, and found that the ra- tio of the mass of nitrogen in relation to the mass of oxygen was 7:8, in a second compound 7:16, and in a third, 7:4. Based on his analyses he for- mulated the law of multiple proportions. This law says that if two elements (A and B) form more than one compound, then the ratios of the masses of element B which combine with a fixed mass of A, are small integers. In 1822, Dalton was elected as a member of the Royal Society and eight years later he was appoint- ed as one of the foreign associates of the French Académie des Sciences. He was highly respected by many scientists in Europe and the King of Eng- land granted him a pension which enabled him to retire from delivering lectures at the Academy. One event in Dalton’s life is especially worth mentioning: One day Dalton decided to visit his mother and gave her a colorful piece of fabric as a gift. He was surprised when his mother said that the fabric was red, because he thought that it was as grey as his coat. He was very concerned about not being able to tell the difference between grey, green, and red. Later, this inability was called dal- tonism after him, or as we now know it, color blindness. John Dalton died in Manchester on July 27, 1844. In his memory, Owens College created a scholarship fund. One of the first students who received it was J. J. Thompson. The atomic mass unit (Da) was named in Dalton’s honor. References: Fierz-Dawid, H. E. (1958). Historia rozwoju chemii. Warsza- wa: Państwowe Wydawnictwo Naukowe. http://www.encyklopedia.pwn.pl http://www.britannica.com http://www.portalwiedzy.onet.pl http://www.wikipedia.pl Wróblewski, A. K. (1998). Wiedza i Życie. Wróblewski, A. K. (2007). Historia fizyki. Warszawa: PWN. Wróblewski, A. K. (1999). Uczeni w anegdocie. Warszawa: Prószyński i Ska. Biography: John Dalton was edited by Stephen Klassen and Cathrine Froese Klassen and is based, in part on Historical Background: Atoms written by Peter Heering. Biography: John Dalton was written by Emilia Dobrowolska with the support of the European Commission (project 518094-LLP-1-2011-1-GR-COMENIUS-CMP) and Polish Association of Science Teachers, Poland. This publication reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein. Dalton Story.pdf Story The teacher and the atoms 1 Storytelling Teaching Model: http://science-story-telling.eu The teacher and the atoms John Dalton was a happy man. He had always wanted to teach, although in the 18th century, this was somewhat unusual for someone from his social status. He was born as the son of a weaver who owned a small piece of land, and like many children of his era, John had to work from the very early age. However, he finally had made it: Since a couple of years, or, to be more precise, since the year 1793, he finally had a position as a lecturer of Mathematics and Natural Philosophy in the New Col- lege of Manchester. Shortly after his appointment, he also had become a member to the Manchester Literary and Philosophical Society, one of the eminent English scientific societies in the late 18th century. Dalton liked it to lecture, actually he had already begun to teach at the age of twelve in a local school. But he also loved science, and his new position offered him the opportunity to combine both his passions. In particular, Dalton liked chemistry, stand- ing in a laboratory and carrying out experi- ments where new substances were created and analyzed was one of those things where he was really good at, and where he was really happy. Recently, chemistry had undergone signifi- cant changes, air had turned out to be a mixture of several gases instead of being an element, and the French Antoine Lavoisier had intro- duced a new chemical system, together with making experiments quantitative and using extremely sensitive balances in order to ana- lyze chemical reactions not only in terms of substances that combine to new substances, but also in a quantitative manner. Even though a lot of chemists were still opposing this new system and this new approach, Dalton loved it. The combination of chemical manipulation and mathematical rigor was something that both met his interest and his competences. And from this new approach, Dalton had developed new insights that he was about to use in his teaching for the first time. He straightened and opened the door to his classroom. As usual, there were the students sitting, and they raised when Dalton entered the room usual, there were chemicals and ap- paratuses on the table. However, this time things would be different. Dalton started to talk, and he talked about the new, quantitative approach in chemistry: He stressed that there are always given rela- tions between the masses of two substances which form in a chemical reaction a new sub- stance. So from this point of view, chemistry was now turning into a mathematical science. The students did not seem to care that much, and Dalton felt some frustration raise, but then Smythe, a boy who was sitting in the first row and was one of the brightest and most interest- ed students in his chemistry class, raised his arm: “Sir, please, may I ask a question?” “Go ahead”, replied Dalton, curious what might be questionable about these simple rela- tions he was just talking about. “Why are there these quantitative ratios be- tween the elements in the chemical reactions?” asked Smythe. “Why?” – this was a thought that had never come to Dalton’s mind. “Why?” Dalton started to think, and stood silent in the classroom. “Why?” None of the writings of the modern chemists was addressing this issue, and nor- mally, they were not even mentioning these ratios. Chemical instructions were somewhat like cooking recipes, you follow them and get the intended results. “Why?” In the end, Dalton straightened and smiled wearily at Smythe: “This is an excellent question, but the chemical theory is not yet at a point where we can answer such a question. Currently, we are collecting data, and it will be one of the future tasks to develop the under- standing of the underlying truths that explain our empirical findings. You see, chemistry is not yet finished.” The boy did not seem to be too pleased with this response, however, he was smart enough to know that he would not get a better response. However, when the lesson was over, Dalton was frustrated, and he could not stop himself from thinking “Why?” What was supposed to be a demonstration of the potential of the new chemistry of Lavoisier, of the powers of the 2 Story The teacher and the atoms Storytelling Teaching Model: http://science-story-telling.eu quantitative approach had turned out to be a disappointment. “Why?” – Dalton felt that this was actually a question that required more thinking and would not to be answered easily. Several years later, Dalton was still thinking about this episode, however, his perspective had changed from initial frustration to fascina- tion. In the meantime he had quit his position at the New College of Manchester, he had be- come an independent chemist who earned his living by teaching children of wealthy Manches- ter industrialists – less teaching load, better payment, and more time for research. Current- ly, he was sitting in a coach to London where he was about to deliver a lecture to the prestigious Royal Institution, a lecture that condensed the findings of his researches of the last years, re- searches that were triggered by this question the schoolboy had asked him. Dalton had been working a lot in the labora- tory, but no longer focusing on the substances that could be composed (or produced by de- composing other substances). Instead, he was trying to find mathematical rules in the chemi- cal reactions that went beyond the recipe ap- proach. The easiest rule (and one that had al- ready been known) had been that chemical substances always react in a certain mass ratio of the initial substances. Moreover, it was strik- ing that there were more quantitative relations involved than one initially anticipated: 2g of Hydrogen react with 16g Oxygen, the same amount would also react with 32g Sulphur. 56g of Iron would also react with 16g Oxygen, the same amount would also react with 32g Sul- phur. Moreover, there were two substances that could be formed from Sulphur and Oxygen – one consisted of 2g Sulphur and 3g Oxygen, the other of 2g Sulphur and 3g Oxygen. There were other chemical substances where similar ratios could be found, and Dalton had had the feeling that there had to be a hidden truth in Nature that could serve as an explanation of these ratios. Why did these chemical substanc- es combine according to fixed numbers, and why did these numbers have a certain ratio with each other? Going through the works of ancient chemists had not been that fruitful – Lavoisier was cer- tainly the master who had laid the foundation to the manner how modern chemistry should be executed. Yet, in his writings was no expla- nation for this behavior. And then, one day, glancing through some old books in the library, he came across an argument of Aristotle who criticized another Greek philosopher, a man called Democritus who had envisioned atoms, smallest, inseparable particles that should form all matter. When reading through this, things became immediately crystal clear to Dalton – this was it, this was the explanation. If there are atoms, then this would explain the quantitative behavior. In the next couple of months, Dalton was rethinking this explanation again and again, was redoing experiments and reexamin- ing evidences, and refining his interpretation. In the end, Dalton had been able to formulate some simple truths that would explain all his chemical findings: 1. Atoms cannot be made or destroyed. 2. All atoms of the same element are iden- tical. 3. Different elements have different types of atoms. 4. Chemical reactions occur when atoms are rearranged. 5. Compounds are formed from atoms of the constituent elements. These five sentences should form the basis of his new chemical theory, and he was going once again through the manuscript of the paper he was to deliver at the Royal Institution. Then, the coach finally arrived in London, and Dalton stepped on the road. Here he was ready to tell the chemists and everyone else who would attend his lecture about his findings. The next day, Dalton stood in the lecture theatre of the Royal Institution – the seats were well occupied, there was a good audience. Dal- ton started to describe his first experiments, gave the numbers of the quantitative analysis, and finally drew his first conclusion: “Matter consists of atoms, small particles that cannot be destroyed or made.” He sensed some disturb- ance in the audience, but continued with his presentation. However, he had more and more the feeling that the discomfort of his audience increased. Finally, he drew his final conclusion: “Atoms are able to explain the chemical behav- ior of substances we know nowadays and are a Story The teacher and the atoms 3 Storytelling Teaching Model: http://science-story-telling.eu valuable tool for the future research.” There was mainly silence in the room, then an elderly scholarly looking man raised and asked a ques- tion that seemed to bother most persons in the audience: “Mr. Dalton, have you ever seen an atom?” There was silence in the room, then Dalton answered: “Umm, well, no, certainly not, but …” The man interrupted: “Well, Mr. Dalton, thank you very much for your … hypothesis, but you know, here in London, we strictly re- strict our science to observable facts …” Dalton felt the blood rushing into his head, and while he looked at the faces of the other attendees, he felt that the presentation he had put so many hopes in was a complete failure. “Thank you, gentlemen, for your time and your attention” was all he could mutter, and then he left the lecture hall hastily. Although Dalton’s theory was adopted by several chemists very quickly, others rejected it. A key problem was the assumption that each element was formed by a different atom, as a result there were about thirty different atoms at the beginning of the 19th century, and their number was increasing. Thus, instead of simpli- fying the structure of matter, Dalton’s atomic theory made nature more complex. For more than 60 years of Dalton’s death the controver- sies about the validity his atomic structure con- tinued. Story The teacher and the atoms was edited by Panagiotis Kokkotas and it is based, in part, on Historical Back- ground: atoms written by Peter Heering and on Biog- raphy: John Dalton written by Emilia Dobrowolska. Story The teacher and the atoms was written by Peter Heering with the support of the European Commission (project 518094-LLP-1-2011-1-GR-COMENIUS-CMP) and the University of Flensburg, Germany. This publication reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein. EN_Guidelines_Dalton.pdf Suggestions to Teachers (Dalton and the atoms) 1 Storytelling Teaching Model: http://science-story-telling.eu Suggestions to Teachers (Dalton and the atoms) Expected results After the lesson, the students are expected to: 1. Verify the power the Dalton’s law about the multiple proportions with the examples of compounds. 2. Apply the Dalton’s atomic theory in the formulation of the particle of water. 3. Write the differences between the Democritus’ atomic theory and the Dalton’s atomic theory. 4. Locate in the narration: a) Dalton’s interpretations for the formulation of some compounds and b) the conclusions which he formulated. 5. Formulate the reasons in which the Dalton’s atomic theory delayed to be accepted by the scientific community. 6. Describe the characteristics of science and the ways it develops, according to the McComas’s list, based on the narration as well as the lesson activities. About the activities of students The proposed students' activities are indicative and they aim at the accomplishment of the above expected outcomes. Moreover, the teacher may choose some of them for the teaching process in relation to its aims, the needs of students and the available time. Finally, she/he can create her/his own activities. About the emergence of the characteristics of science in the narration, these characteristics are quoted in the website, comprehensively (in classification of the stories by NOS). About the locating of the characteristics of Nature of Science in the proposed activities, indicatively, we can quote the following: A) The activity 3 concerns the characteristic of Nature of Science: a) “Science demands and relies on empirical evidence” and b) “Science has a subjective element”. B) The activity 4 concerns the characteristics of Nature of Science: a) “Science has a subjective element” and b) “Science demands and relies on empirical evidence”. C) The activity 5 concerns the characteristic of Nature of Science: “Science demands and relies on empirical evidence”. D) The activity 6 concerns the characteristic of Nature of Science: “There are historical, cultural, and social influences on science”. E) The activity 7 concerns the characteristics, which are quoted in the previous activities: 3, 4, 5 and 6. 2 Suggestions to Teachers (Dalton and the atoms) Storytelling Teaching Model: http://science-story-telling.eu Suggestions to Teachers (Dalton and the atoms) were written by Aikaterini Rizaki and Panagiotis Kokkotas with the support by the European Commission (Project 518094-LLP-1-2011-1-GR-COMENIUS-CMP) and the NKUA of Greece. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained there in. EN_LA_Dalton.pdf Student’s Learning Activities (Dalton and the atoms) 1 Storytelling Teaching Model: http://science-story-telling.eu Student’s Learning Activities (Dalton and the atoms) Activity 1 You will watch a video with narration or listen to a story from your teacher about John Dalton and his atomic theory. Please write the most important points of the story according to your view and discuss them in your group. (Indicative important points of this story: description of Dalton’s atomic theory, the methodology which Dalton used to explain his theory, how science is developed,…) …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………..………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………… Activity 2 Please watch the video (http://www.youtube.com/watch?v=HFF-2wyyTKc) and try to apply the atomic theory of Dalton in the formation of chemical formula of water. …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………..………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… http://www.youtube.com/watch?v=HFF-2wyyTKc 2 Student’s Learning Activities (Dalton and the atoms) Storytelling Teaching Model: http://science-story-telling.eu …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………… Activity 3 Based on the Dalton’s law, please prove that, this law is also valid when the elements Copper (Cu) and Oxygen (O) react and form two different compounds, Oxide and Sub Oxide of Copper (atomic weight of copper: 63.5, atomic weight of oxygen: 16). …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………..………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………….…… …………………………………………………………………………………………………………………………………………………… ………………………………………… Activity 4 In the diagram in the following website, please find combinations of compounds in which the law of the multiple proportions is valid. (http://www2.honolulu.hawaii.edu/instruct/natsci/science/brill/sci122/Programs/p25/p25.html #3. John Dalton). …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………… Activity 5 Student’s Learning Activities (Dalton and the atoms) 3 Storytelling Teaching Model: http://science-story-telling.eu Please write a paragraph (500 words) to explain the differences between the atomic theories of Democritus and Dalton. …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………..………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… ……………………………… Activity 6 How do you explain the delay of 60 years after Dalton’s era for the scientific community to accept his atomic theory? …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………..………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… ………………………………………… Activity 7 Using the list of ideas that describe the characteristics of science and the ways it develops, try to locate and write these ideas in the story you heard and the activities of this lesson. These ideas that scientists call Nature of Science (Nature Of Science-NOS- ) are: Characteristics of Nature of Science (NOS) 1. Science demands and relies on empirical evidence. 2. Knowledge production in science includes many common features and shared habits of mind. 3. Scientific knowledge is tentative but durable. 4. Laws and theories are related but distinct kinds of scientific knowledge. 5. Science is a highly creative endeavor. 6. Science has a subjective element. 7. There are historical, cultural, and social influences on science. 4 Student’s Learning Activities (Dalton and the atoms) Storytelling Teaching Model: http://science-story-telling.eu 8. Science and technology impact each other, but they are not the same. 9. Science and its methods cannot answer all questions. Scientists argue that in order to learn science one must first understand what exactly science is. Because it is difficult to define science, scientists give a list of its characteristics. …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………..………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………… Student’s Learning Activities (Dalton and the atoms) were written by Aikaterini Rizaki and Panagiotis Kokkotas with the support by the European Commission (Project 518094-LLP-1-2011-1-GR-COMENIUS-CMP) and the NKUA of Greece. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained there in. Historical background atoms.pdf Background Atomsatoms 1 Storytelling Teaching Model: http://science-story-telling.eu Background atoms The concept of Atoms is fundamental to our modern scientific understanding of the world. The em- inent physicists Richard P. Feynman pointed out that “[i]f, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generations of crea- tures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or the atomic fact, or whatever you wish to call it) that all things are made of atoms – little particles that move around in perpetual motion, attracting each other when they are little distance apart, but repelling upon being squeezed into one another” (Feynman et al. 1963, I- 3). This quotation is for several reasons relevant with respect to this historical background: On the one hand, Feynman is pointing out extremely clear how important the concept of an atomic struc- ture of matter is to modern science. Yet, he also raises implicitly another issue that is very relevant if the genesis of this concept is analysed: Feynman speaks in this introduction to the first lecture of the ‘atomic hypothesis (or the atomic fact, or whatever you wish to call it)’, and in doing so he ad- dresses and ignores at the same time a crucial detail: is the existence of the atom an hypothesis, or is it a fact, and if so, what really is part of this fact – which level of description can still be taken as being a fact, which are additional hypothesis. Feynman ignores this issue by leaving it to the reader how she or he wishes to call it – this appears to be a crude form of relativism that can possibly be explained by looking at the date of the publication: Feynman’s lectures date from the early 1960s, for that time it appears to be questionable whether a different position could be expected in epis- temological or in nature of science categories. Such a statement appears to be somewhat irritating from our point of view, yet, it demonstrates how far the knowledge about the nature of science has developed in recent decades. In order to teach this central concept, one aspect gets relevant which was also important in the historical development but will not be discussed in this historical background: The notion of a chemical element is a prerequisite for the formulation of the atomic model – this can be seen in the historical analysis booth for the development in the Greek antiquity as well as for the modern period, and it can also be identified in the educational conceptions. How- ever, the historical development of the concept of elements will not be discussed in this back- ground material but is assumed to already ex- ist. Ancient discussions about the structure of matter The question how the material world is structured has been discussed in particular in Greek Antiquity (a knowledge which is in part due to the transfer of knowledge from this pe- riod to the Early Modern Era in Europe).1 In this respect, the topic of a prime element that 1 There is evidence that models of the material world existed also in the Indian culture as well as in Babylonian culture, however, documentation is poorer and these concepts have not played any role in the introduction of an atomic theory into Europe- an science – thus they are not discussed in the back- ground. constitutes all the other substances becomes relevant, however, it is of course not even syn- onymous with a simplistic atomic concept as this prime element could exist without any corpuscular structure. Philosophers such as Thales of Miletus, Anaximenes, Heraclites and Empedocles were among those scholars who developed or promoted respective conceptions. About 450 BC, two philosophers developed ideas that are relevant to the introduction of the atomic conception: Democritus and Leucip- pus. Both postulated that the material world is made from very tiny particles, which them- selves cannot be any further separated into smaller parts. These atoms were distinguished from each other by their shape and size. Ac- cording to Democritus, these atoms move in the empty space and collide with each other. By specific combinations of atoms, other sub- stances are formed, yet, these combinations are not permanent but the atoms can separate again. However, the concepts of Leucippus and Democritus were not accepted by their con- temporaries: “Two factors weighed against any widespread acceptance of the classical version of atomism. The first factor was the uncom- promising materialism of this philosophy. By explaining sensation and even thought in terms of the motions of atoms, the atomists chal- lenged man’s self-understanding. Atomism seemed to leave no place for spiritual values. 2 Background Atoms Storytelling Teaching Model: http://science-story-telling.eu Surely the values of friendship, courage, and worship cannot be reduced to the concourse of atoms. Moreover, the atomists left no place in science for considerations of purpose, whether natural or divine. The second factor was the ad hoc nature of the atomists’ explanations”. (Loose 2001, 25) Additionally, there was a rival concept which appeared superior as it ex- plained the behavior of matter: the four ele- ments conception which explained all existing matter as well as its properties through four elements: Water, Air, Fire, and Earth.2 A central, if not the central figure for the re- jection of this atomic theory was Aristotle, who advocated the four elements theory and added as a fifth: ether, which filled the space between the celestial bodies. This was relevant as – ac- cording to Aristotle – no empty space could exist – the horror vacui, nature’s ‘fear’ of emp- tiness. Moreover, according to his conception, everything in nature is intentional; there is no superfluous action in nature. Additionally, each object has a natural position, and if displaced, it aims at getting back to this position. Conse- quently, Aristotle was able to explain observa- ble processes with his principles. The atomists were not only unable to propose a superior explanation, even more: they assumed the ex- istence of particles no one could see. This was a major criticism Aristotle made against the atomic theory, apart from that he did not ac- cept the idea of the empty space which was according to his own conception impossible. And a permanent motion appeared absurd in Aristotle’s understanding. All in all he opposed the atomic concept which was in contradiction to several of his central beliefs. Yet in some sense he is still relevant to the modern devel- opment of the atomic theory as the original works of Leucippus and Democritus were lost and were actually known only through his criti- cism. Aristotle’s works were kept and expanded in the Islamic culture, and through this culture, they came back to Europe and the Christian culture. For the scholastic period, this Aristote- lian understanding became dominant, particu- larly as it was considered to be coherent with 2 It has to be understood that these elements were not what we call Earth, Fire, Air, and Water, but they are elementary principles (see also the background on the development of the Periodic Table). the Bible. Yet, astronomers and slightly later natural philosophers developed a different understanding of natural processes – conse- quently the authority of Aristotle was more and more questioned throughout the 17th and 18th centuries – at the end of this period, it was the experimenting enlightened natural philosopher who was considered to be able to uncover the laws and structure of nature. In this process some experiments and considerations were developed that seemed to strengthen the an- cient atomic hypothesis. Of particular im- portance was the demonstration of the exist- ence of the vacuum.3 In another argumentation it was discussed that if a tiny bit of incense is burned, it can be smelled in the entire room. As this room is significantly bigger than the space the incense initially occupied, the initial piece has to be divided into more than 750.000.000 parts – these calculations were intended to show how small the particles have to be that form the piece of incense (see Beer & Pricha 1997). However, such a discussion remained on the level of simple calculations, there was no claim whatsoever that atoms exists or what their properties might be. Such an understand- ing was only developed in the early 19th centu- ry. Structuring matter: Dalton When looking into the genesis of modern science, probably the first scholar to establish an atomic conception is John Dalton, a chemist who was following Lavoisier’s new, quantita- tive approach towards chemistry. Using a bal- ance to analyze chemical reactions formed a major achievement of Lavoisier’s new chemical system, and this enabled chemists to take a different perspective on chemical reactions. Lavoisier himself established the difference towards classical chemistry and the novelty of his approach several times, to give but one ex- ample: “Lavoisier wrote in the Opuscules phy- siques et chimiques (1774) that he ‘applied to chemistry not only to the apparatus and meth- ods of experimental physics but also the spirit of precision and calculation which characteriz- es that science’.” (Nye 1993, 35). Yet, it was not only the methodological step or conceptual modifications that made Lavoisier’s chemistry 3 On some of the controversies with respect to the existence of a vacuum and the related philosophical implications see Shapin & Schaffer 1989. Background Atoms 3 Storytelling Teaching Model: http://science-story-telling.eu distinct to the previous understanding. A key element in his chemistry was the different no- tion of chemical reactions that helped him to use the quantitative description, and the un- derstanding that ‘simple substances’ can be interpreted as elements that cannot be decom- posed any further. In this respect, Lavoisier stated explicitly: “I shall, therefore, only add upon this subject, that if, by the term elements, we mean to express those simple and indivisi- ble atoms of which matter is composed, it is extremely probable we know nothing at all about them; but if we apply the term elements, or principles of bodies, to express our idea of the last point which analysis is capable of reaching, we must admit, as elements, all the substances into which we are able, to reduce bodies by decomposition.“(Lavoisier 1794, xxiii) Remarkably, Lavoisier is already using the term ‘atom’, even though he is not using an atomic theory. However, this notion of element that gets evident in this quotation is also rele- vant to the introduction of the atomic theory. A key understanding resulted from the quantitative observations at the end of the 18th century: most compounds are the result of the reaction of specific ratios of masses of the ele- ments that form this compound. This rule be- came known as the law of constant composi- tion. Even though this law appeared to be valid for the chemical reactions that had been ana- lyzed quantitatively, there was another striking aspect, and this was first characterized by John Dalton. Dalton realized that there were some chemical reactions in which different com- pounds were formed through a combination of the same elements (i.e. from a reaction of cop- per with oxygen two different compounds can result, likewise carbon and oxygen, and so on). The resulting compound depended on the amount of the two initial substances that react- ed with each other. However, there was also some regularity that Dalton noticed: there was a ratio of small integer numbers between the masses of element A that reacted with the same amount of element B to two different com- pounds. From this finding Dalton formulated another law. the law of multiple proportions characterizes that if two elements possibly re- act to more than one compound, then the masses of element A reacting with the same amount of B are small integer multiples. This law, together with the law of constant composi- tion, forms the starting point towards the stoi- chiometric approach in chemistry. However, even though this law was based on empiric evidence, it was not the only conclu- sion that Dalton drew from his experiments: In a lecture delivered at the Royal Institution London4, he proposed the following ideas which form the basis of the modern atomic theory of matter: “All matter is composed of atoms Atoms cannot be made or destroyed All atoms of the same element are identical Different elements have different types of atoms Chemical reactions occur when atoms are rearranged Compounds are formed from atoms of the constituent elements.”5 Evidently, Dalton’s use of the term atom is different to the one of Lavoisier. Dalton’s con- ception of the atom is characterized by their countability, they have a certain weight and so on, whilst in Lavoisier’s conception it is more their chemical property which is relevant, and it is even unclear whether this is an actual par- ticle. This assumption enabled Dalton to prepare an explanation of the stoichiometric laws he and others had formulated. According to this understanding, the law of constant composition results both from the understanding that all atoms of the same element are identical, and that chemical reactions are a result of the rear- rangement of the atoms. The law of multiple proportions can then be interpreted as being the result of different arrangements of the at- oms that result in different compounds. In do- ing so, the knowledge about quantitative chem- ical analysis became based on a first paradigm in the Kuhnian sense (and in this respect, one could argue that this achievement turned stoi- chiometric chemistry into a science in the Kuhnian sense). Yet, things were not that easy: Even though Dalton’s theory was adopted by several chemists very quickly, others rejected it. A key problem was the assumption that each element was formed by a different atom, as a result there were about thirty different atoms at the beginning of the 19th century, and their number was increasing. Thus, instead of simpli- fying the structure of matter, Dalton’s atomic 4 According to Clarke (1803), the first presentation was made at the Manchester Philosophical Society. 5 http://www.rsc.org/chemsoc/timeline/pages/1803 .html, last access April 18, 2012 4 Background Atoms Storytelling Teaching Model: http://science-story-telling.eu theory made nature more complex. Despite this criticism, the stoichiometric laws were used by chemists, and some of them used fractional numbers to express the ratio of masses – indi- cating that there was no inseparable particle. This was not just a problem of initial ac- ceptance, even sixty years later, reservations against this theory were stated very explicitly, e.g. the President of the Chemical Society Wil- liamson stated in a speech in 1869: “… that on the one hand, all chemists use the atomic theo- ry, and that, on the other hand, a considerable number of them view it with distrust, some with positive dislike.“ (quoted in Tilden & Glasstone 1926, 227). And some renown chem- ists and physicists at the beginning of the 20th century still rejected the atomic theory – we will come back later to this issue. Yet, particu- larly for chemists, the atom became an entity that was used in their analysis of chemical reac- tions. However, it was not considered to be real (neither in the positivistic sense nor in the sense of a relevant theoretical description) but just a heuristic tool which was very adequate in terms of describing chemical reactions, but had nothing to do with the actual understanding of matter (Görs 1999). The atom gets established Despite the discussions amongst the chem- ists who accepted the atom as a useful hypoth- esis, the physicists started to use the atom as a real object with explanatory power. Particular- ly the developing science of thermodynamics played an important role in the establishment of a physical atom that is crucial for the kinetic theory (atoms in motion represent heat). How- ever, this understanding was strongly criti- cized, particularly in the German speaking sci- entific community by eminent scientists such as Ernst Mach, Wilhelm Ostwald and Georg Helm.6 The controversy between these re- searchers (Ostwald was a Nobel Prize winner in 1909, Mach was also very prominent in his times) and the proponents of a statistical inter- pretation (most notably Boltzmann) was not just based on physical issues but involved also deep philosophical questions. A key aspect in 6 For other reasons, also Max Planck initially criti- cized atomism as he understood it in Boltzmann’s statistical interpretation, see Müller (2008). This discussion was not limited to the German speaking community; another example of the opponents of atomism is Poincare this respect was the question whether individ- ual atoms can be seen, or whether there is any evidence for the existence of individual atoms. Actually, at the beginning of the 20th centu- ry, it appeared that the atomic theory was con- sidered to be overthrown, and Boltzmann to be a relic from the 19th century. Things changed significantly when Planck’s theory of radiation was established and at about the same time Einstein and Smoluchowski published their interpretation of Brownian motion. This was a phenomenon described already in the 18th century by several observers. However, it was attributed to the biologist Robert Brown who noticed in the early 19th century that small pollen and dust particles that are floating on water moved in an erratic manner. The re- markable detail about this motion was that it never appeared to stop, moreover, the moving particles were certainly not alive. It remained an open question for about half a century how this motion was to be interpreted. Even though towards the end of the 19th century some re- searchers proposed solutions to this question which correspond to our interpretation, it was only in 1905/06 when Albert Einstein and Mar- ian Smoluchowski presented independently their mathematical analysis of Brownian mo- tion (actually Einstein’s paper was one of the three famous in his annum mirabilis, the other two dealt with the photoelectric effect and the special theory of relativity). Both researchers were able to explain that the motion can be caused by the motion of the particles of water due to their kinetic energy – thus, Brownian motion appeared to be a first macroscopic ef- fect that had to be explained with the assump- tion of small particles and thus forming an em- pirical evidence for the kinetic theory and thus for the atomic theory. Actually, Ostwald is said to have been convinced of the adequateness of the atomic theory through the agreement of the description and the empirical data. At about the same time, there was another empirical evi- dence for the adequateness of the atomic theo- ry, and this one is said to have convinced Mach: When radioactive particles are placed next to a fluorescent screen, minute flashes of light can be observed which are to be interpreted as results of individual α-particles. Thus, within a few years, the understanding of atomism had changed from almost complete rejection to almost complete acceptance. Boltzmann, the great proponent of the atomic theory, was at Background Atoms 5 Storytelling Teaching Model: http://science-story-telling.eu that time already dead – he committed suicide in September 1906. The atom gets a substructure Even before Einstein’s and Smoluchowski’s work helped to establish a consensus about the correctness of the atomic description of matter, some researchers established empirical results that actually contradicted the initial under- standing of the atom as being inseparable: Ac- tually Faraday’s work on electrolysis – which dated from the 1830s –could have been raised questions on the fundamental and inseparable nature of the atom as formulated by Dalton: According to Faraday’s investigation, a certain amount of electricity releases a certain amount of an element in the process of electrolysis. However, this empirical result did not raise questions with respect to the atomic nature of matter, on the contrary: It remained unclear until well into the 20th century whether elec- tricity has an atomic structure, or whether the ratio between electrical charge and released matter was the mean of several reactions that could take place at the same time. Only in the 1920’s, when Millikan’s measurements on the elementary charge were awarded with the No- bel Prize, this issue had been settled (at least for the vast majority of scientists, see Holton 1978). Yet, towards the end of the 19th centu- ry, further evidence was produced that ques- tioned the indivisible character of the atom. Actually, the starting point was research that in retrospect can be taken as being further evi- dence for the atomic theory, even though it was not interpreted in this sense in the historical situation. In the 1860’s, the chemist Bunsen showed, together with the physicist Kirchhoff, that the light emitted from a substance is very characteristic and that only special frequencies (or lines, if the spectrum is analysed) are emit- ted (or absorbed). This provided also a method to identify new elements, and the number of elements increased significantly over the next few years. Analysing spectra was a major issue, and became expanded towards analyzing also cathode rays and their interaction with gases that are filled into the tubes. In doing so, exper- imentalists had hoped to develop a further un- derstanding about the constitution of matter (Müller 2004). Particularly the analysis of cathode rays appeared to be very promising; among the researchers working in this field was J.J. Thomson. Thomson analyzed these cathode rays and established that they are formed by particles7 which have a mass of about 1/1000 of the hydrogen atom. He was also able to determine the mass-charge ratio by deflecting these particles in a magnetic field. However, what might be more relevant to this discussion are his experiments in which he used different cathode materials to emit the rays (which were basically emitted by heating up the cathode, the rays were then accelerated with an electric field). Thomson could show that all particles have similar properties, no matter from which material they were emanat- ed. This could be seen as an indication that these particles (corpuscles, as Thomson called them) were a fundamental part of matter. However, there was a problem: When these corpuscles were that lightweight, but electrical- ly charged, and they form a part of matter, then how can stability be created? Thomson finally came up with a solution: “We suppose that the atom consists of a number of corpuscles mov- ing about in a sphere of uniform positive elec- trification …” (Thomson 1904, 255).8 This meant that the (at this time still disput- ed atom) was no longer indivisible, and that the model of the atom had to be modified. Another modification became necessary soon after- wards, and this was related to another field which emerged in the very early 20th century: radioactivity - which will be discussed in the next chapter. One of the researchers who estab- lished their scientific career in analyzing this phenomenon was Ernest Rutherford, a physi- cist from New Zealand who did his early re- searches (which won him the Nobel Prize) in Canada and then moved to England again. In the Cavendish laboratory two of his assistants – Marsden and Geiger – carried out the experi- ment to scatter α-particles with metal foils (Geiger & Marsden 1909). 7 Quite remarkably, his son George Paget Thomson was also awarded the Nobel Prize in physics, this time for his work on electron diffraction. In some sense, it could be (admittedly oversimplified) ar- gued that J.J Thomson was awarded the Nobel Prize for demonstrating that electrons were particles, whilst his son was awarded the same honor for demonstrating that electrons are no particles but have also a wave character. 8 Actually the Japanese physicist Nagaoka came up with a similar solution one year earlier. 6 Background Atoms Storytelling Teaching Model: http://science-story-telling.eu Rutherford had already suspected that a scattering is possible when he observed the passage of α-particles through sheets of mica. This experiment was taken up again, and the result was more than irritating (even though not completely unexpected: Geiger and Marsden observed that even though the vast majority of α-particles passed the metal foil (and in the course of the experiment they used gold foil as this could be prepared extremely thin), with some of them being scattered, very few of them were reflected. “In retrospect, Marsden’s discovery was the ‘most incredible event’ that had ever happened to him [Rutherford, PH], almost as incredible, he would say, as if a fifteen-inch shell fired at a piece of tissue paper bounced back and hit the gunner. That the military imagery and the in- credulity are later fabrications we can see easi- ly from a lecture Rutherford delivered … six month after the discovery of the diffuse reflec- tion (Heilbron 1981, 264f.) Be this statement as it may, the result was certainly unexpected to the scientific communi- ty, and Rutherford came up with an explanation that was certainly also unexpected: He calcu- lated from the behavior of the α-particles that the atom had a small positively charged nucle- us that contains almost all the mass, whilst most of the space of the atom was empty, ex- cept for the electrons that moved around somewhere in this space. Atoms can change As already mentioned, Rutherford became famous for his researches in radioactivity – yet he was not the person to open this field. The first researcher who actually observed radioac- tivity was the French physicist Henri Becquerel – his discovery (and one can use this term as this was completely unexpected even though some sensibility for radiation effects certainly existed due to Röntgen’s demonstration of the X-rays) opened a new field. Yet, this field was not entered immediately by Becquerel himself or other scientists, but the rays emitted from Uranium salts were just considered to be a cu- riosity not worth any further scientific atten- tion. It was the collaboration of a young Polish chemist with a French physicists that actually made the importance of this new field evident: Marie and Pierre Curie could use the radiation to show that within several radioactive samples other elements than Uranium have to exist as the radiation was stronger than the one emit- ted from pure Uranium. In a long and laborious analysis, they were finally able to prepare pure samples of the elements Polonium and Radium. Particularly Radium became central to the re- search in the new field of radioactivity as it was fairly active and produced different rays. Yet, it became evident, that a lot more chemical ele- ments have the ability to emit such a radiation. However, there were several things that turned out to be really astonishing – among them cer- tainly the transformation of one element into another in the process of an α- or a β-decay. This gets evident from an anecdote that brings us back to Rutherford: “Rutherford and Soddy found, for example, that radioactive thorium, atom by atom, was gradually turning itself into radium. At the moment he realized this, Soddy … blurted out, ‘Rutherford, this is transmuta- tion!’ ‘For Mike’s sake, Soddy,’ his companion shot back, ‘don’t call it transmutation. They’ll have our heads off as alchemists” (Weart 1988, 5f.). Already the work of the Curies’ had estab- lished a fundamental idea: The radiation of a material is related to some properties of the element. Uranium has a different radiation than Polonium and Radium, and so on. Moreover, it became evident through experiments that the activity of a sample gets reduced over time – which is evident when the transformation of the atoms into those of another element is tak- en into consideration. However, there was also a problem with respect to the decrease of the activity, it became evident that the half-life was not a value that could be used for an individual atom, on the very contrary. The law of radioac- tive decay worked only for a statistical sample, a prognosis of the behavior of the individual atom was not possible. Initially, this was taken to be an indication of the required development in atomic physics, however, it became evident in the end that this is simply not possible and the decay can only be described mathematical- ly in terms of the statistic of the ensemble. Moreover, in analyzing the radiation, three different types could be identified and soon characterized. Another surprise came with the α-rays – they turned out to be helium, an ele- ment that until then was only detected in the Background Atoms 7 Storytelling Teaching Model: http://science-story-telling.eu sun (with spectroscopic methods) and seem- ingly did not exist on Earth. Yet, as the α-rays appeared to be positive particles whilst the β- rays were electrons, this meant that not only the electrons could be emitted from the atom but also some of the positive substance. Physical atoms and chemical atoms Determining the properties of the different rays was one of the first things that experi- menters did once it became evident that this was a relevant topic. Among other things, mass and charge of the particles that formed the rays were determined. This was done by applying a well defined magnetic field rectangular to the direction of the rays – from the deflection the charge/mass ratio could be determined. A comparable set-up was used to analyze atoms, and this provided another insight into their structure as well as it solved one of the remain- ing problems. Particularly through the work of Francis Aston, who modified this set-up into a mass spectrometer, it became evident that even though from a chemical point of view all atoms of an element are indistinguishable, this was not the case from the physical point of view. Aston could demonstrate that for several ele- ments different atoms existed that could be distinguished (and only be distinguished) from their mass. This helped to explain why certain elements had an atomic weight that was not an integer multiple of the mass of the hydrogen atom. From Aston’s data it became evident that the atomic weight was the weighted mean of the atoms’ mass. Looking at the masses of each kind of atoms (which were predicted and called isotopes already before by Rutherford’s collab- orator Soddy) it became evident that the atom- ic weight of each individual isotope was (within the accuracy) an integer multiple of the Hydro- gen atom. Atoms can be changed Whilst most experiments with radioactive substances aimed at analyzing the radiation, some researchers also attempted to modify atoms (artificial ‘transmutation’). Initially, α- particles were used, they were shot towards matter and it could be observed that some at- oms were able to integrate the α-particle in the nucleus, thus forming a new element. The first to establish this experiment was again Ruther- ford who could show that when α-particles are sent through Nitrogen, Hydrogen and Oxygen are traceable. Rutherford’s interpretation was that the Nitrogen nucleus was absorbing an α- particle, and the newly formed nucleus would immediately emit a hydrogen nucleus. This was the first successful attempt to modify an ele- ment and to create a new one – other such ex- periments quickly followed. Yet, it has to be understood that this is not a nuclear fission, this was still considered to be impossible. Rutherford named the Hydrogen nucleus proton, and postulated that this proton is an elementary component of all nuclei. Yet, the mass of the nuclei does not form integer multi- ples of the mass of the proton, this was still a major problem. At the same time, two more questions still existed: Why can positive pro- tons form the nucleus, and how to explain a β- decay. Rutherford assumed that also electrons exist in the nucleus and form pairs together with protons, and these pairs should keep the elementary particles in the nucleus together. Among the researchers that tried to investi- gate the nucleus and the atom through interac- tion with α-particles were Irène Joliot-Curie (daughter of Marie Curie) and her husband Frédéric. They repeated some experiments which had been carried out in Berlin: Beryllium was irradiated with α-particles; as a result a significant radiation could be observed which they initially took as γ-rays. The particles of this radiation were not charged and appeared to have an extremely high energy. Even though the particles were not charged, they could in- teract with hydrogen and release electrons. Whilst the Joliot-Curies kept their interpreta- tion of the result of their experiments being γ- radiation, James Chadwick, who was working with Rutherford, choose a different interpreta- tion. According to Chadwick this radiation was to be explained with a new corpuscle and thus the radiation was a completely new type. Fur- ther experiments showed that the particles had a rest mass similar to the proton, and could be seen as the particle that replaces the proton- electron-pair Rutherford had assumed to ex- plain the (relative) stability of the nucleus. The neutron enabled further experiments on transmutation, as it is neutral, there is not the repulsive electrostatic force that was a problem in attempting to get an α-particle into the nucleus. Several researchers worked on 8 Background Atoms Storytelling Teaching Model: http://science-story-telling.eu this field as it enabled the creation of new radi- oactive isotopes as well as new products of decay. Among those researchers were the Jo- liot-Curies in Paris, Fermi in Italy, and Hahn and Strassmann in Berlin. Both aimed at getting a neutron into the nucleus of Uranium, at that time the heaviest element to be known. The idea was to produce the so-called transuranium elements, elements with a greater atomic num- ber than Uranium. This appeared to be the only possibility to develop new elements as the Pe- riodic Table was considered to be complete. Particularly the chemist Hahn was very un- satisfied with his results: It appeared that through his experiments, Uranium had been turned into Barium – which has significantly lesser atomic weight than Uranium. Hahn ad- dressed this issue in a letter to the physicist Lise Meitner. She had been working with Hahn for a long time and recently had to flee to Swe- den from the threat of fascist Germany after the so-called Anschluss of Austria. Meitner re- sponded initially that such a result does not seem to be plausible.9 However, as she pointed out in the same letter, there had been so many surprises in the history of radioactivity that one could hardly could say, this or that is impossi- ble. Hahn insisted that he had verified Barium, and Meitner pointed out in another letter writ- ten a couple of days later that at least from the energetic point of view, a fission could have occurred. In a discussion she had with her nephew Frisch, Meitner came to the idea that possibly the model of the atom had to be thought like a drop – if an object with adequate energy hits that drop, breaks this drop into two smaller ones. Hahn finally published his findings (togeth- er with Strassmann) and pointed out that for him as a chemist, he had to state that the result- ing isotopes behave like Barium, yet he claimed that from the point of physics he was still not convinced that this element could be produced in such an experiment. This changed very quickly, and scientists immediately pointed out that in such a reaction not only a significant amount of energy would be released, but also 9 Before these experiments were carried out, how- ever, the concept of nuclear fission had already been formulated by Ida Noddack already in 1934 when she was criticizing the discussion of Fermi in his experiments on transurane elements. other neutrons, thus, a chain reaction appeared possible. Note that some audiofiles with Protagonists such as Thomson, Rutherford, Hahn etc. are to be found at http://www.aip.org/history/mod/fission/fissi on1/01.html I am indebted to D. Metz (University of Win- nipeg) for his careful proof-reading as well as for comments on the previous version of this background material. References Heidelberger, M. (1993). Die innere Seite der Natur : Gustav Theodor Fechners wissenschaftlich- philosophische Weltauffassung. Frankfurt am Main: Klostermann. Heilbron, J. L. (1981). Historical studies in the theory of atomic structure. New York: Arno Press. Holton, G. J. (1978). The scientific imagination : case stud- ies. Cambridge [Eng.]; New York: Cambridge University Press. Lavoisier, A. L. (1794). Elements of Chemistry. Transl. by Kerr, 4th ed., Edinburgh: William Creech. Losee, J. (2001). A historical introduction to the philoso- phy of science. Oxford [England]; New York: Oxford University Press. Morgenweck-Lambrinos, V., & Trömel, M. (2001). Wissen- schaft und Legende: eine Nachbetrachtung zu Lise Meitner, Otto Hahn und die Kernspaltung: eine Legende aus unseren Tagen. NTM, 9, 29--40. Müller, F. (2004). Gasentladungsforschung im 19. Jahr- hundert. Berlin: Verlag für Geschichte der Naturwissen- schaften und der Technik. Müller, I. (2008). Ein Leben für die Thermodynamik. Vom Zweiten Hauptsatz der Thermodynamik zum Planck- schen Wirkungsquantum. In: Physik Journal 7/3, 39-45. Nye, M. J. (1993). From chemical philosophy to theoretical chemistry : dynamics of matter and dynamics of disci- plines, 1800-1950. Berkeley u.a.: Univ. of California Press. Rife, P. (1992). Lise Meitner: ¬Ein Leben für die Wissen- schaft. Hildesheim: Claasen. Shapin, S., & Schaffer, S. (1989). Leviathan and the Air- Pump: Hobbes, Boyle, and the Experimental Life (1st Paperback Edition ed.). Princeton: UP. Sichau, C. (2005). Atomphysik : historische und fachliche Materialien zur Unterrichtsvorbereitung. Oldenburg: Didakt. Zentrum (diz). Background Atoms 9 Storytelling Teaching Model: http://science-story-telling.eu Simonyi, K. (1995). Kulturgeschichte der Physik: von den Anfängen bis 1990 (2. Aufl. ed.). Thun, Frankfurt/Main: Deutsch. Thomson, J.J. (1904). “On the structure of the atom: an investigation of the stability and periods of oscillation of a number of corpuscles arranged at equal intervals around the circumference of a circle; with application of the results to the theory of atomic structure”. In: Philo- sophical Magazine 6 Volume 7, Issue 39, 237-265 Tilden, W. A., & Glasstone, S. (1926). Chemical discovery and invention in the twentieth century. London: Routledge. Weart, S. R. (1988). Nuclear fear : a history of images. Cambridge, Mass.: Harvard University Press. Background atoms was edited by S. Klassen Background atoms was written by Peter Heering with the support of the European Commission (project 518094- LLP-1-2011-1-GR-COMENIUS-CMP) and the University of Flensburg, Germany. This publication reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the infor- mation contained therein Historical Ressources.pdf A Primary Spurces Dalton, John: A New System of Chemical Philosophy I 1808, online available: http://archive.org/details/newsystemofchemi01daltuoft. Dalton, John: A New System of Chemical Philosophy II 1827, online available: http://archive.org/details/newsystemofchemi02daltuoft. Dalton, John et. al.: Foundations of the Atomic Theory 1893, online available: https://archive.org/details/ost- chemistry-foundations_of_the_atomic_theory. B Secondary Sources Baxter, Roberta: John Dalton and the Development of Atomic Theory, Greensboro, N.C. 2013. Fernandez, Bernard: Unravelling the Mystery of the Atomic Nucleus: A Sixty Year Journey 1896 - 1956, New York, NY 2013. MacDonnell, John J.: The Concept of an Atom from Democritus to John Dalton, Lewiston u.a. 1992. Patterson, Elizabeth C.: John Dalton and the Atomic Theory: The Biography of a Natural Philosopher, Garden City, NY, Anchor Books Ed. 1970. Roscoe, Henry Enfield: John Dalton and the Rise of Modern Chemistry 1895. Roscoe, Henry Enfield/Harden, Arthur: A New View of the Origin of Dalton’s Atomic Theory, New York, NY u.a., Repr. 1896, 1970. Thackray, Arnold: John Dalton; Critical Assessments of his Life and Science, Cambridge 1972. links.pdf http://www.youtube.com/watch?v=lYoH242X2q4&
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