1. PSC 4010 Nuclear Technology: A matter of Energy

2. PSC 4010: Chapter 2 Goals: _ SWBAT put the different atomic theories in a historical and technical context _SWBAT compare the current simplified atomic model with all precedent models and theories

3. PSC 4010: Chapter 2 What is a theory? An organized set of laws designed to show that a scientific system is valid. For this purpose, theories use scientific models Theories can: _be supported by facts _be rejected by experimental evidence _sometimes take long to be proven true (or not)

4. PSC 4010: Chapter 2 Brainstorm: What is a model? A model is a physical representation of something we cannot see (even without visible proofs we can demonstrate the existence of objects and explain their nature)

5. PSC 4010: Chapter 2

6. A bit of history… (pp. 2,3 – 2,7)  Ancient Greeks  Naturalists (nature could work on its own, following laws and not controlled by gods)  What is matter composed of?

7. PSC 4010: Chapter 2 Leucippus  Inventor of “Atom”  “Atomos” (Indivisible)  Observing dust particles, concluded that matter is composed of infinitely small particles that could no longer be divided

8. PSC 4010: Chapter 2 Democritus  Disciple of Leucippus  Developed first Atomic Theory  “Matter is discontinuous”  There are gaps between atoms. These always move and can combine together

9. PSC 4010: Chapter 2 Empedocles  Theory of four elements  “Matter is continuous”  All substances are made of Water, Earth, Air and Fire

10. PSC 4010: Chapter 2 Aristotle  Theory of four elements (as Empedocles)  The four elements can combine to form other substances by the influence of Moisture, Dryness, Cold and Heat (diagram p. 2,5)

11. PSC 4010: Chapter 2  Theory of four elements continued for about 2000 years until…  18 th century, Water is discovered to be made of hydrogen and oxygen  18 th century, Air is discovered to be a mixture of many gases

12. PSC 4010: Chapter 2 1.Matter is continuous ____ 2.Matter is made of very small particles ____ 3.Developed first atomic theory____ 4.Four elements combine to form new substances____ 5.Invented word “Atom” ____ 6.First to talk about 4 elements____ 7.Matter is discontinuous____ L: Leucippus D: Democritus E: Empedocles A: Aristotle E L D A L E D

13. PSC 4010: Chapter 2 Purely theoretical ideas since they had no technical means of proving their hypotheses

14. PSC 4010: Chapter 2 Uniform matter (no gaps) Tiny particles (atoms) with gaps between them Matter is composed of indivisible atoms Matter is discontinuous

15. PSC 4010: Chapter 2 What have we learned about the different atomic theories and their historical and technical context? Industrial Revolution _The very small universe _The structure of matter What is matter composed of? _Matter is continuous, discontinuous, indivisible, four elements Ancient Greeks (Naturalists) _Development of thinkers and Philosophers End of four elements theory _New discoveries (chemistry & electricity)

16. PSC 4010: Chapter 2 More history…  Renaissance (14 th to 17 th century)  Growing interest in physical world (geography and astronomy)  Europe wanted to extend borders of known world and extend its influence to Africa and the Orient  Increment in international trade  Discovery of New World (America)

17. PSC 4010: Chapter 2 And then came…the Industrial Revolution  New discoveries (chemistry and electricity)  Scientific world interested in the very small universe and the structure of matter

18. PSC 4010: Chapter 2 Dalton’s model (pp. 2,10 – 2,14)  An element is a collection of identical atoms  A compound is a combination of different atoms  Different elements have different masses  Organized known elements according to their relative masses (compared to Hydrogen, the lightest, considered of unit value, e.g. = 1)  His model did not include the presence of charges

19. PSC 4010: Chapter 2 Secondary IV Textbook (MELS) « The Material World » Chapter 1: Atoms and Elements

20. PSC 4010: Chapter 2 Leucippus & Democritus had done so Dalton thought atoms were indivisible Dalton thought atoms of same element were identical

21. PSC 4010: Chapter 2 Thomson’s model (pp. 2,18 – 2,20)  Bringing a magnet near a cathode ray tube (flow of electrons between two electrodes in a vacuum), made the flow bent  This was a proof that atoms possess charged particles  He called those particles Electrons, and decided they had negative charge  Since atoms are neutral, they must have positive charges, and also these charges should be in identical number with the negative ones

22. PSC 4010: Chapter 2 Secondary IV Textbook (MELS) « The Material World » Chapter 1: Atoms and Elements

23. PSC 4010: Chapter 2 Dalton thought atoms were indivisible and had no charges. Thomson’s model has a divisible atom (can be divided into positive and negative particles) The electron (negatively charged) Thomson though electrons were scattered throughout a positively charged sphere, thus neutrality was achieved (charged muffin)

24. PSC 4010: Chapter 2 Rutherford’s model (pp. 2,20 – 2,23)  Bombarded a thin sheet of gold with fast moving alpha particles (positively charged, to be studied later)  Gold can be stretched and made extremely thin  Proved that matter (atoms) consist mostly of empty space (Matter is discontinuous: Democritus)  Almost all atomic mass is concentrated in a small nucleus with a very strong positive charge  The positively charged particles in the nucleus were called Protons  The nucleus would be surrounded by a cloud of very light electrons

25. PSC 4010: Chapter 2

27. Most particles bombarded were not deflected _Positive: positive bombarded particles were repelled _Dense: positive bombarded particles bounced back _Compact: only a few of bombarded particles seemed strike nucleus

28. PSC 4010: Chapter 2 Protons Positive Negative electrons would crash into the positive nucleus (Thomson-like model)

29. PSC 4010: Chapter 2 Bohr’s model (pp. 2,23 – 2,24)  Added the idea of energy levels, where electrons revolve around the nucleus in fixed levels or shells

30. PSC 4010: Chapter 2

31. Chadwick’s model or the Simplified Atomic Model (pp. 2,24 – 2,30)  Tried to respond to the question: how could positively charged particles in the nucleus stay together and not repel?  Concluded that neutral particles must also be in the nucleus, between the protons, in order to separate them and thus decrease any force of repulsion. He called those neutral particles Neutrons  A much stronger force must therefore exist in the nucleus, operating at very small distances, to keep the nucleus from disintegrating. This is the nuclear force, and will be studied later in this module

32. PSC 4010: Chapter 2

33. Neutron Neutron must exist in order to keep the nucleus from disintegrating due to the electrostatic repulsions of positively charged protons

34. PSC 4010: Chapter 2 What have we learned about the evolution of the Atomic Model? Dalton’s (solid indivisible balls, no charge, different masses) Thomson’s (positive nucleus, embedded with negative electrons) Rutherford’s (atoms are mostly empty space, most mass is found at nucleus, light electrons surround it) Bohr’s (electrons revolve around nucleus in fixed levels or shells)

35. PSC 4010: Chapter 2 What is the new atomic model? How are the other models added to it?

36. PSC 4010: Chapter 2 Evolution of the atomic model:  New subatomic particles have been discovered (not part of this program)  Atoms are neutral, therefore # protons = # electrons  Protons and neutrons are very heavy (compared to electrons) and have similar masses  Electron configuration: arrangement of electrons around the nucleus of an atom (you must know the name of the first 20 elements of the Periodic Table for Chapter 3)

37. PSC 4010: Chapter 2 Electron configuration: arrangement of electrons around the nucleus of an atom (you must know the name of the first 20 elements of the Periodic Table for Chapter 3) For our purposes (20 first elements), each level has a maximum of: _First level: 2 electrons max _Second level: 8 electrons max _Third level: 8 electrons max Examples: Nitrogen (Atom. Num 7, so 7 protons, and also 7 electrons): 2e, 5e Silicon (Atom. Num 14, so 14 protons, and also 14 electrons): 2e, 8e, 4e Calcium (Atom. Num 20, so 20 protons, and also 20 electrons): 2e, 8e, 8e, 2e

38. PSC 4010: Chapter 2

42. Practice Exercises for Chapter 2:  Page 2.33 – 2.36 – Ex 2.24 – 2.38