Atomic Mass

Atomic Number (A) Number of protons in the nucleus Atoms of the same element all have the

same number of protons In a neutral atom, the total number of

protons is equal to the total number of electrons

Mass Number (Z) Total number of protons and neutrons in

nucleus Electrons are so small, there mass is

insignificant to the atomic mass

Example How many protons, neutrons, and electrons

in

1) 3H

2) 235U

3) carbon-12

4) magnessium

5) 41Ca2+

6) 81Br -

Isotopes Atomic masses can be different for atoms

of the same element if they have different numbers of neutrons

Atoms with different masses are called Isotopes or Nuclides