4.1 Defining the Atom

1. Early Models Democritus(about 400BC)-matter composed of tiny, indivisible particles 4.1 Defining the Atom Dalton(about 1800)- - used scientific method transformed Democritus’ ideas into theory

2. 4.1 Defining the Atom

3. Atoms of element A are identical Atoms of element B are identical, but different than element A A and B can be chemically combined as a compound Atoms of element A and B can be physically mixed together

4. Dalton Proposed All elements composed of tiny, indivisible particles Atoms of an element are identical & distinct from atoms of other elements Atoms can form compounds, combining in simple whole-number ratios Atoms can be rearranged (chemical reactions), but atoms of one element do not change into atoms of another element.

5. Sizing Up the Atom 5x10-11 - 2x10-10 Atoms cannot be seen with a light microscope A tunnelling electron microscope can make images of atoms like this:

6. Tunnelling Electron Microscope Atoms cannot be seen with a light microscope

7. 4.2 Structure of the Nuclear Atom Subatomic Particles Atoms not indivisible Electrons Protons Neutrons

8. Electrons Discovered 1897 by J.J.Thomson Used cathode ray tube to show electrons are negatively charged

9. Electrons Discovered 1897 by J.J.Thomson Used cathode ray tube to show electrons are negatively charged Deflected by magnet

10. Electrons Discovered 1897 by J.J.Thomson Used cathode ray tube to show electrons are negatively charged Deflected by electrical charge

11. Electrons Discovered 1897 by J.J.Thomson Calculated charge/mass ratio The ratio of charge to mass was the same, regardless of gas in cathode tube. Conclusion? Electrons must be present and the same in all elements.

12. Electrons

13. Robert A Millikan 1916 oil drop experiment Electrons Millikan calculated the mass of an electron Mass or electron = 1/1840 mass of a hydrogen atom Charge = -1

14. Robert A Millikan 1916 oil drop experiment Electrons The actual apparatus used in the Millikan oil drop experiment

15. Atoms are neutral When charges do exist, they are always in simple multiples of the charge on an electron (no fractions) Eugen Goldstein 1886 found cathode ray evidence of protons Proton- charge of +1 mass 1840 times mass of electron (1 atomic mass unit) Neutrons and Protons

16. Neutrons Not discovered until 1932 by James Chadwick Neutrons and Protons Neutrons have no charge have a mass similar to proton

17. “Plum pudding,” model Electron, “raisins,” stuck in a lump of positive, “dough.” Atomic Nucleus Disproved in 1911 by one of Thomson’s students, Ernest Rutherford

18. Rutherford’s Gold Foil Experiment Alpha particles shot at a thin piece of gold foil did not pass right through with slight deflection. Instead, most passed straight through. Some bounced right back!

19. Rutherford’s Gold Foil Experiment Rutherford concluded that •Most of the atom is empty space •All of the positive charge and almost all of the mass is Concentrated in the tiny core, “nucleus.” composed of protons and neutrons. An idea of the size: Atom = football stadium Nucleus = marble

20. 4.3 Distinguishing Atoms Atomic number = number of protons Defines the element! Atoms are electrically neutral therefore atomic number also is the number of electrons

21. Copy and complete the table: Subatomic particles 19 B 5 5 16 16 23 23

22. Fluorine 9 b. Calcium 20 c. Aluminium 13 How many protons and electrons?

23. number of protons + number of neutrons = mass number Therefore mass number - number of protons = number of neutrons Helium with a mass number of 4 has 2 protons. How many neutrons does it have? (Atomic) Mass Number 2 neutrons

24. mass number symbol atomic number Isotope Notation Au 197 (number of protons + neutrons) First letter always capitalized Second letter never capitalized 79 (number of protons) How many neutrons does an atom of gold-197 have? 118 neutrons

25. O S Br 16 32 80 Ag c. a. b. 108 35 16 8 47 Pb d. e. 207 82 How many neutrons p112 q17 61 neutrons 8 neutrons 16 neutrons 45 neutrons 125 neutrons

26. C F Be 12 19 9 6 9 4 Express in Isotope Notation p112 q18 a. Carbon-12 b. Fluorine-19 c. Beryllium-9

27. C F Be 12 19 9 6 9 4 Express in Isotope Notation p112 q18 a. Carbon-12 b. Fluorine-19 c. Beryllium-9

28. Ne Ne Ne 21 20 22 10 10 10 Neon-20 Isotopes 10 neutrons Neon-21 11 neutrons Neon-22 12 neutrons Isotopes have different # of neutrons, same # of protons and electrons

29. O O O 16 17 18 8 8 8 Use isotope notation to show Oxygen-16 Oxygen-17 Oxygen 18 Q19 p113 Q20 How many neutrons in each?(Chromium’s atomic number=24) Chromium-50 Chromium-52 Chromium-53 26 neutrons 28 neutrons 29 neutrons

30. Atomic Mass Unit 1/12 mass of an atom of carbon-12 Since carbon 12 has 6 protons and 6 neutrons, Mass of 1 proton is about 1amu Why isn’t the atomic mass = atomic mass number? Atomic Mass

31. Weighted average of the mass of all naturally occurring isotopes. To find atomic mass, calculate (Mass of isotope)•(%abundance as decimal) For each isotope And add the results together Atomic Mass

32. Atomic Mass Carbon is 98.89% Carbon-12 & 1.11% Carbon-13 Its atomic mass would be (12amu•0.9889)+(13.03amu•0.0111) = 12.011 amu

33. You CAN do this. Work out the example if you are stuck. It’s like this: Carbon is made up of 98.89% Carbon-12 & 1.11% Carbon-13 Its atomic mass would be (12amu•0.9889)+(13.03amu•0.0111) = 12.011 amu Chemistry Warm Up

34. Try to answer these without your notes or the book, then go back and check your answers against your notes or the book. When you finish, complete the second version of Reading & Processing Information from the Periodic Table (worksheet) Chemistry Warm Up

35. Horizontal row = period Atomic number increases left to right Atomic number increases as you go down Properties vary as you go across a period Vertical column = group Groups have similar chemical properties Periodic Table