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

2. An Atom is Like… 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. Atom Facts! 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. Atomic Number Atomic Mass
Tells you the identity of the element (Each element has a different atomic #)
Atomic Mass

5. Practice!
Given the following atomic numbers, determine the identity of the elements: Atomic # Element 16 Sulfur 9 Fluorine 53 Iodine

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

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

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

9. Isotope Facts!
Important things to remember about the isotopes of an element!
Same Element
Same # Protons
Different # Neutrons
Different Masses

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

11. Isotope Symbols OR 11H or Hydrogen-1 1 proton 0 neutrons
Mass number
Hydrogen-3 OR
11H or Hydrogen-1
1 proton
0 neutrons
21H or Hydrogen-2
1 proton
1 neutron
31H or Hydrogen-3
1 proton
2 neutrons

12. Mass Number The mass number = # protons + # neutrons Mass Number = 3
(So, if you know the # protons, you can figure out the #
neutrons, and vice versa!)
Example: 31H or Hydrogen-3
# Protons = 1
Mass Number = 3
Mass number = # protons + # neutrons
= x
x = # Neutrons = 2

13. Practice!
Determine the # of protons and neutrons for each of the following isotopes: 168O 8 protons, 8 neutrons 2110Ne 10 protons, 11 neutrons Flourine-19 9 protons, 10 neutrons Boron-11 5 protons, 6 neutrons

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

15. Add all of the answers from step 1 above.
Ave. Weighted Mass
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. Ave. Weighted Mass
Calculate the average weighted mass (the atomic mass) of nitrogen.
Isotope Mass Relative % Abund.
Nitrogen amu
Nitrogen amu
Step 1
(14.003)(0.9963) = amu
(15.000)(0.0037) = amu
Step 2
= amu
Mass
% Abund. (as a decimal)

17. Practice!
Calculate the average weighted mass (the atomic mass) of Silicon.
Isotope Mass Relative % Abund.
Silicon amu
Silicon amu
Silicon amu
Step 1: Step 2:
(27.977)(0.9223) = amu =
(28.976)(0.0467) = amu amu
(29.974)(0.0310) = amu

18. Electrons 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. Ions!
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. Ca2+, Na1+, Al3+
Anions: Ions formed when atoms gain one or more electrons – have a negative charge
Ex. F1-, P3-, O2-

20. Practice!
Determine the number of electrons for each element: Element # Electrons S 16 S2- 18 Al 13 Al3+ 10

21. Finished!