1. Protons, Neutrons, Electrons/Isotopes/Average Atomic Mass

2. If an atom was the size of a football stadium … the nucleus (protons + neutrons) would be a marble on the 50 yard line the electrons would be smaller than gnats out in the stands Gnat-sized electron Marble -sized nucleus

3. Important things to remember about atoms! Most of an atom is empty space Electrons are so small, we can pretend that their mass is zero The mass of an atom is from its nucleus (protons & neutrons)

4. Tells you the identity of the element (Each element has a different atomic #) Atomic Mass

5. Given the following atomic numbers, determine the identity of the elements: Atomic #Element 16 9 53

6. Also tells you the number of protons (Each element has a different # of protons) Atomic Mass

7. Determine the number of protons for each element: Element # Protons chlorine arsenic oxygen 17 33 8

8. Isotopes = Different versions of the same element Isotopes of Carbon

9. Important things to remember about the isotopes of an element! Same ElementSame # ProtonsDifferent # NeutronsDifferent Masses

10. Relative Percent Abundance = The overall percent of each isotope of an element Isotopes of Carbon

11. 1 1 H or Hydrogen-1 1 proton 0 neutrons Mass number Hydrogen-3 OR 2 1 H or Hydrogen-2 1 proton 1 neutron 3 1 H or Hydrogen-3 1 proton 2 neutrons

12. The mass number = # protons + # neutrons (So, if you know the # protons, you can figure out the # neutrons, and vice versa!) Example: 3 1 H or Hydrogen-3 # Protons = 1 Mass Number = 3 Mass number = # protons + # neutrons 3 = 1 + x x = # Neutrons = 2

13. Determine the # of protons and neutrons for each of the following isotopes: 16 8 O 21 10 Ne Flourine-19 Boron-11 / 8 protons, 8 neutrons 10 protons, 11 neutrons 9 protons, 10 neutrons 5 protons, 6 neutrons

14. The Atomic Mass is the average weighted mass of the isotopes of an element Atomic Mass

15. To calculate the average weighted mass (atomic mass of an element: Step 1 Multiply each isotope’s mass x its % abundance. (Make sure the % abundance is in decimal form!) Step 2 Add all of the answers from step 1 above.

16. Calculate the average weighted mass (the atomic mass) of nitrogen. Isotope Mass Relative % Abund. Nitrogen-14 14.003 amu 99.63 Nitrogen-15 15.000 amu 0.37 Step 1 (14.003)(0.9963) = 13.951 amu (15.000)(0.0037) = 0.055 amu Step 2 13.951 + 0.055 = 14.006 amu Mass % Abund. (as a decimal)

17. Calculate the average weighted mass (the atomic mass) of Silicon. Isotope Mass Relative % Abund. Silicon-28 27.977 amu 92.23 Silicon-29 28.976 amu 4.67 Silicon-30 29.974 amu 3.10 Step 1: (27.977)(0.9223) = 25.803 amu (28.976)(0.0467) = 1.353 amu (29.974)(0.0310) = 0.929 amu Step 2: 25.803+1.353+0.929 = 28.085 amu

18. Tells you the number of electrons too! Remember! The atomic # also tells you the number of protons (so…the # protons = # electrons in an atom)

19. When an atom loses or gains one or more electrons, it becomes an ion. There are two kinds of ions: Cations: Ions formed when atoms lose one or more electrons – have a positive charge Ex. Ca 2+, Na 1+, Al 3+ Anions: Ions formed when atoms gain one or more electrons – have a negative charge Ex. F 1-, P 3-, O 2-

20. Determine the number of electrons for each element: Element # Electrons S S 2- Al Al 3+ 16 18 13 10