Chapter 4

1. Chapter 4 The Structure of Atoms

2. Scientists • Democratus • Developed atomos • All matter is made of particles • Aristotle • Earth, wind, water, and fire • Said Democratus was wrong • He was believed for 2000 years • John Dalton • Atomic Theory • “Father of Atomic Theory”

3. 5 Points of Dalton’s Atomic Theory • Elements are made of extremely small particles called atoms. • Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. • Atoms cannot be subdivided, created, or destroyed. • Atoms of different elements combine in simple whole-number ratios to form chemical compounds. • In chemical reactions, atoms are combined, separated, or rearranged.

4. Scientists • Crooks • Cathode Ray Tube • Indicated all matter contained electrons • TV • He saw electrons but didn’t know it • JJ Thomson • Discovered electrons • Measured the charge to mass ratio of an electron • Millikan • 1909 Oil drop experiment • He determined the charge of the electron • Found within 1% of the mass of an electron

5. Scientists • JJ Thomson • Plum Pudding Model of Electrons • Pudding is positive and plums are negative

6. Scientists • Rutherford • Gold foil experiment • Hypothesized that when he shot a beam of alpha particles through a sheet of gold foil that the particles would move straight through. This would have proven the plum pudding model to be true.

7. Gold Foil Experiment • Rutherford saw that the alpha particles (+) were deflected. • This meant that there was a positive mass in the center of the atom.

8. Scientists • Chadwick • Neutron discovery • National Origin of Scientists • Millikan was the only American • Why? • War, fighting, building a nation

9. People in the World vs Atoms in a Penny • 6000000000 • 29000000000000000000000 • Which is people on Earth and which is atoms in a penny?

10. 3 Atomic Particles • Proton • + • In the nucleus • Neutron • 0 • In the nucleus • Electron • - • Outside the nucleus

11. What Makes Up Atomic Mass? • Protons and nuetrons • Pg 97 • Why are electrons not included?

12. Spacing in a Hydrogen Atom • I am the nucleus of a hydrogen atom. • My electron would be as far away as the football field. • Most of the atom is empty space

13. Atomic number = number of protons • Mass number = number of protons and neutrons • In a neutral atom the number of protons is equal to the number of electrons. • An isotope is an atom of the same element with a different number of neutrons.

14. What determines the type of atom? • Protons • Why are electrons important? • Bonding • What do neutrons do? (What is the charge of a proton? Where are they located?) • Provides nuclear stability • Allow protons not to repel each other

15. 107Ag 109 Ag 47 47 • 107 and 109 are the mass numbers. • 47 is the atomic number. • The silver with a mass number of 107 has 60 neutrons. • The silver with a mass number of 109 has 62 nuetrons. • These are isotopes of silver. • There are 47 electrons in this neutral atom.

16. Of the following, which cannot be changed without changing the element? • Mass number • Number of protons • Number of electrons

17. Amu • Unit for measuring atomic mass • Based on carbon 12 • Defined as 1/12 of the mass of a carbon 12 atom • This is much easier than measuring in grams. • 1 x 10 -24

18. Average Atomic Mass • Located below the chemical symbol • Why is it a decimal number? • It is a weighted average of isotopic masses

19. Example: There are two isotopes of Boron, B-10 and B-11, B-10 is found 19.8% of the time and B-11 is found 80.2% of the time. B-10 has a mass of 10.013 amu and B-11 has a mass of 11.009 amu. What is the average atomic mass? • (10.013 amu) .198 + (11.009 amu) .802 = 10.811 amu

20. Pg 112 59-68 • Pg 805 Compare and contrast chemical and nuclear reactions using a Venn diagram. • Pg 821-826 Compare and contrast nuclear fusion and fission using a Venn diagram.

21. Chemicalvs Nuclear Reactions • 2H2 + O2 2H20 • In this chemical reaction all the bonds are broken and reformed. • Most reactions occur this way. • The elements are not changed • Valence electrons are used in bonding.

22. Chemicalvs Nuclear Reactions • What can change the rate of a chemical reaction? • Temperature • Pressure • Concentration of reactants • Catalyst

23. Chemical vsNuclear Reactions • The only thing the two have in common is that they both involve atoms. • Nuclear reactions emit particles or rays • Not all atoms can do this • They emit huge amounts of energy that involve protons, neutrons, and electrons. • The rate at which this occurs cannot be changed by anything. • Atoms change from one type to another

24. Fusion vs Fission Fusion Fission Atom is broken Uranium-235 Usually produces radioactive products Atomic bomb • Atoms combine • Thermochemical Reactions • Light atoms (Usually H) fuse to make bigger atoms • Usually does not produce radiation • Extreme energy to initiate • Usually very high temps. • H bomb and the sun

25. Radiation Table Particle symbol Emitted Charge Approximate Energy 4He 2 α 5 MeV Toward - Alpha + 2 4α 2 .05 to 1 MeV Toward + 0β -1 0e -1 - 1 Beta 1 MeV ϒ 0 Gamma

26. This must be obeyed! • Nuclear reactions must mass balance and charge balance

27. Alpha Decay • Emits α particle • Mass number will decrease by 4 and the atomic number will decrease by 2. • Where will the particle show up in a chemical equation? • With the products Ex. 230Th4 He + 226 Ra 90 2 88

28. You do this alpha decay problem Po 218 84

29. Po 218 4 He + Pb214 84282

30. Beta Decay • Remember: nuclear reactions must mass balance and charge balance. • What happens • A nuetron becomes a proton and a beta particle is emitted 1 N 0β + 1 P 0 -1 +1 • The mass number does not change and the atomic number increases by 1.

31. Beta Decay Example 234Th0β + 234 Pa 90 -1 91 You do 82Pb210 You should get 83 Bi 210

32. Gamma Decay • No mass and no charge • Accompanies alpha or beta

33. Positron Decay 1 P 0β + 1 N 11 0 This is the positron

34. Pg 814 #9 a, b, and c • Pg 837 # 69 a and b

35. Carbon Dating • Uses radioactive isotopes • Carbon is in all living things • 2 isotopes of Carbon • Carbon 12 and Carbon 13 • Carbon 13 is the radioactive isotope • How does it work? • When you are alive you maintain a stable amount of Carbon 13. When you die it starts to diminish. We use the amount remaining to establish age.

36. Carbon Dating Amt remaining = (initial amt) ½ t/T t – time elapsed T – half life Half life – time required for half of the radioactive nuclei to decay into stable atoms

37. The half life of C-13 is 5,730 years • 70 atoms of C-13 5,730 years • 35 atoms of C-13 5,730 years • 17 or 18 atoms of C-13 • 9 atoms of C-13 5,730 years • This is how we carbon date • It takes a very long time to get to 0

38. Can you carbon date a rock? • No, rocks have never been alive • You can date rocks but you must use a different isotope.

39. Are protons and neutrons the smallest thing in the nucleus? • No, there are subatomic particles called quarks • Quarks have a charge and they give the particles that they make up a charge. • Electrons are made of leptons.