1. Counting Subatomic Particles

2. Mass Number vs. Atomic Number
Atomic Mass or Mass Number
Sum of the protons and neutrons in the nucleus of an atom
Atomic mass unit or amu
Atomic Number
Equals the number of protons
In a neutral atom, protons = electrons

3. Counting Subatomic Particles
Atomic Mass = Protons + Neutrons
The atomic mass must be given. The atomic mass on the periodic table is an AVERAGE atomic mass.
Atomic Number = Number of Protons
All neutral atoms will have the same number of protons and electrons.

4. Finding Atomic Mass and Number
Element Name
Atomic Number
Element Symbol
Average Atomic Mass

5. Bromine - 80 Atomic mass = 80 amu Atomic number = 35 Protons = 35
Electrons = 35
Neutrons = 45
80-35 = 45

6. Sulfur - 32 Atomic mass = 32 amu Atomic number = 16 Protons = 16
Electrons = 16
Neutrons = 16
32-16 = 16

7. Nickel- 59 Atomic mass = 59 amu Atomic number = 28 Protons = 28
Electrons = 28
Neutrons = 31
59-28 = 31

8. Oxygen - 16 Atomic mass = 16 amu Atomic number = 8 Protons = 8
Electrons = 8
Neutrons = 8
16-8 = 8

9. Copper - 64 Atomic mass = 64 amu Atomic number = 29 Protons = 29
Electrons = 29
Neutrons = 35
64-29 = 35