1. 8th Grade Physical Science Mrs. Fletcher
Masses of Atoms
8th Grade Physical Science
Mrs. Fletcher

2. Essential Question: What is the difference between atomic number and atomic mass?

3. Fun Fact:
Smaller particles of matter called quarks exist but scientist still consider atoms the basic building blocks of matter.

4. Atomic MAss
Composed mostly of protons and neutrons in the nucleus – also called mass number.

5. Atomic Number
The atomic number is equal to the number of protons in an atom.
The number of protons also identifies the element.

6. Can you identify the atomic Mass and Atomic Number?

7. How do I find the number of Electrons?
The number of electrons will always be equal to the number of protons.
Assume that the atom is neutral so the number of electrons have to be equal to the number of protons.
For Example Helium
Protons: 2
Neutrons: 2 (How did you find the # of neutrons?
Electrons: 2

8. How do I find the number of Neutrons?
To find the number of neutrons in an atom subtract the atomic number from the mass number.
Formula:
# Neutrons= mass number – atomic number
How many neutrons are in the nucleus of Lithium? (Don’t forget to round) 4

9. Common Mass Numbers Use your periodic table to fill in the CHart
Elements
Symbol
Atomic #
Protons
Neutrons
Mass #
Boron
Carbon
Oxygen
Sodium
Copper