1. -Different FORMS of an Element that occur Naturally -Have the SAME # of P and E but DIFFERENT # of N -Isotopes of an element have the SAME CHEMICAL PROPERTIES 12 C 14 C 6 ATOMIC MASS ATOMIC # 6 N = 12 -6 = 6 N = 14-6 = 8

2. - Average Mass of all ISOTOPES of an element Average Atomic Mass = Isotope Mass + Isotope Mass # of Isotopes

3. - Contains PROTONS and NEUTRONS - Is extremely TINY compared to the size of the atom - Has most of the MASS of the atom

4. If PROTONS are POSTIVE, and LIKE CHARGES REPEL, why don’t PROTONS REPEL EACH OTHER? What keeps them in the NUCLEUS? THE STRONG FORCE -Keeps Protons and Neutrons stuck together -100X larger than electric force -SHORT-RANGE force = quickly becomes weak as distance between P and N increases THE ELECTRIC FORCE -Force than makes like charges repel -Makes Protons repel each other -LONG-RANGE force = strong force even when Protons are far apart

5. As NUCLEUS SIZE INCREASES: -STRONG FORCE stays about the SAME -ELECTRIC FORCE becomes GREATER LARGE NUCLEUS IS NOT HELD TOGETHER AS TIGHTLY!

6. STABLE Nucleus = Strong Force can hold the nucleus together permanently UNSTABLE (LARGE) Nucleus = Strong Force isn’t large enough to hold the nucleus together tightly UNSTABLE NUCLEUS = DECAYS (breaks apart) giving off matter and energy = RADIOACTIVITY

7. Nucleus Stability depends on the RATIO of NEUTRONS to PROTONS Nuclei with TOO MANY or TOO FEW Neutrons compared to Protons = RADIOACTIVE Small Nucleus = 1 Neutron :1 Proton ratio for stability Large Nucleus = 3 Neutrons : 2 Protons for stability

8. The Heat/Energy released by DECAY 3 Types:1. Alpha 2. Beta 3. Gamma

9. -Made of 2 Protons and 2 Neutrons -Are the same as a HELIUM NUCLEUS -Have an Electric Charge (2 +) - Least PENETRATING form of radiation = can be stopped by a sheet of paper - Can damage human cells - More MASSIVE than Beta or Gamma He 4 2

10. - The changing of one element into another through decay (ADD to CHART) Alpha particles = element looses 2 protons/2 Neutrons The NEW ELEMENT: New atomic # is 2 LESS New mass # is 4 LESS

11. -Neutron decays into a PROTON and emits an ELECTRON (Beta particle) - Faster and MORE penetrating than alpha - Stopped by aluminum foil - Can damage human cells - New elements atomic number is increased by 1 - New elements mass is the same

12. -Not particles, they are WAVES -Emitted during Alpha and Beta Decay -MOST PENETRATING radiation -Have HIGH FREQUENCIES/SHORTEST WAVELENGTHS -No mass, no charge, travel at the speed of light -Need thick blankets of LEAD/concrete to stop them - Cause LESS damage to human cells

13. -Amount of time it takes for 1/2 of a radioactive nucleus to decay to a stable isotope -Stable isotopes left after the decay = DAUGHTER ISOTOPE -Half-life is different for different elements

14. -Using half-lives to determine the age of materials 1: Compare the amount of Radioactive Isotope to the amount of Daughter Isotope in the sample 2. Calculate the # of half-lives 3. # of Half-lives = Age of the material Ex: Carbon Dating = C-14 = 5,730 years = plant/animals Uranium Dating = Rocks