Atomic and Mass number

1. Atomic Theory

2. • Atomic number is the number of Protons in an atom
• All atoms of a particular element have the SAME number of protons (All
Carbon atoms have 6 protons)
• In a neutral atom,
The atomic number =The number of electrons

3. • Also called atomic weight or Mass Number
• Sum weight of protons and neutrons in an atom

4. Calculate the mass number of each of
the following atoms

5. O
8
16
Atomic
number
Mass
number
Symbol
OxygenName
Atomic number= Number of protons= Number of electrons
Mass number= Number of protons + Number of neutrons

6. Calculating Neutrons:
• Mass number = protons + neutrons
so…..
• Neutrons = mass number – protons
What is the number of neutrons of the following atom ?
A
21
45