1. Atoms and Subatomic Particles
Atoms are the basic building blocks of all matter.

2. Subatomic Particles That Make Up Atoms
There are 3 types of subatomic particles.
1. electrons (e–) : outside nucleus
“-” charge
very little mass
2. protons (p+) : make up nucleus
“+” charge
1 amu (atomic mass unit)
3. neutrons (n0): make up nucleus
no charge
1 amu

3. Atomic Number and Mass Number
Elements are often symbolized with their atomic number and average atomic mass number.
Mass number and atomic number can be found using the periodic table. 17 Cl
35.453
Atomic number
Average atomic mass

4. Calculating Subatomic Particles
1. You need your Periodic Table to determine protons, neutrons and electrons.
Protons = the atomic number
Electrons = the atomic number (in a neutral atom) 17 Cl
35.453

5. Calculating Subatomic Particles
Neutrons = Mass # - Atomic #
Example
Round the average atomic mass to the nearest whole number (for Cl, rounds to 35)
Neutrons = Mass # - Atomic #
Neutrons = – = 18 17 Cl
35.453

6. Calculate # of p+, n0, e– for Ca, Ar, and Br.
Atomic
Mass p+ n0 e– Ca 20 40 20 20 20 Ar 18 40 18 22 18 Br 35 80 35 45 35