1. Atoms
Chapter 4

2. Protons Positively charged = +1 Approximately 1 amu (atomic mass unit)
Located in the nucleus

3. Neutrons Neutrally charged = 0 Approximately 1 amu
Located in the nucleus

4. Electrons Negatively charged = -1 Relatively small mass (0.0005 amu)
Located in the space surrounding the nucleus

5. Atoms
Neutral charge
Same number of protons as electrons to balance the charge
Atomic number = # protons and # electrons
Atomic mass = # protons + # neutrons

6. Isotopes Same number of protons (atomic number the same)
Different number of neutrons (atomic mass different)

7. Ions Same number of protons (same atomic number)
Same number of neutrons (same approximate atomic mass)
Different number of electrons (has a charge)

8. Regular Average All samples are weighted equally
Example : If a student took 5 tests each test is worth 1/5th or 20% of the final grade
Can multiply each test by 1/5th
OR add all the tests and divide by 5

9. Weighted Average Not all samples are weighted equally
Example: A student takes 5 tests. The first test is worth 40%, the second is worth 30%, and the other are each worth 10%
Multiply each test by what it is worth
Add up
Atomic weight on periodic table

10. Radioactive Decay
Chapter 4 and Chapter 25

11. Radioactive Decay
The tendency of an element to spontaneously emit radiation until it forms a stable atom
Unstable nuclei based on ratio of neutrons to protons
Often results in the formation of a different element
Radioisotopes: isotopes of atoms with unstable nuclei

12. Stability Ratio between neutrons:protons
Closer to 1:1 = more stable (elements of atomic number < 20)
Closer to 1.5:1 = more stable (elements with very large atomic numbers)

13. Types of Radioactive Decay: Alpha Particle
2p+, 2n
2+ charge on particle
Basically an He atom
Slow moving and not good at penetrating
Happens to very large atoms
Lose both proton and neutrons

14. Types of Radioactive Decay: Beta Particles
-1 charge
Move very fast
Neutron breaks down to a proton and an electron
Loses a neutron and gains a proton
Happens to really large atoms

15. Types of Radioactive Decay: Gamma Particles
Mostly energy
Has 0 mass
No charge
Accompanies alpha and beta radiation
Cannot form new atoms

16. Types of Radioactive Decay: Positron Emission
Emission of a positron from the nucleus
Positron = particle the same mass as an electron but the opposite charge
Proton converted to neutron and positron
Loses proton, gains neutron
Happens to very small atoms

17. Types of Radioactive Decay: Electron Capture
Nucleus draws in a surrounding electron
Combines with a proton to form a neutron
Loses a proton, gains a neutron
Happens to small atoms
Also emits a photon

18. Nuclear Reactions Atomic number and atomic mass are conserved
Reactants = products
Problems p. 837

19. Transmutation
The conversion of one atom of an element to another element
Via nuclear reactions
Can happen naturally (all elements above #83)
OR can be induced

20. Half - Life Radioactive decay can be measured in half-lives
Half-life = time required for one half of a radioisotope’s nuclei to decay
Amount remaining = initial amount * 0.5^n
n = the # of half-lives
n = t/T where t = elapsed time, T = half life

21. Nuclear Reactions

22. Nuclear Reactions Much more powerful than chemical reactions
Energy released is greater
Fission and Fusion

23. Fission
Heavy, unstable atoms fragment into smaller atoms to increase their stability
Initiate by hitting with a neutron
Smaller products form, extra neutrons
Extra neutrons can trigger more fission reactions = chain reaction
Atom must be big enough to initiate and maintain a chain reaction = critical mass

24. Fusion Small atoms bind to create more stable atoms
Release large amounts of energy
Take really high heat to initiate and maintain reaction (40 million K)
Thermonuclear reactions

25. Nuclear Power Plants Fission Reactions
Fuel rods contain large atoms (uranium- 235)
Additional rods contain atoms that can absorb extra neutrons
Positioning can determine how many neutrons are absorbed and the speed of the rxn

26. Power Generation Fission reactions produce a lot of heat
Heat absorbed by a cooling system of water
Used to generate steam that drives turbines to produce power

27. Problems
Tight balance between out of control chain reactions and producing adequate power
Continual adjustment
Some products are extremely radioactive with long half-lives, waste
Containment structures to shield radioactivity