Atoms Ions and Compounds.

 Isotopes: Atoms of the same element with different numbers of neutrons and different masses.

Isotopes are of the same element and have;

• Different masses
• The same number of protons and eletrons
• A different number of neutrons in the nucleus

Isotopes of the same element have the same chemical properties because;

• Chemical reactions involve electrons
• Neutrons make no difference to chemical properties

Most elements contain a mixture of isotopes, each in a different amount (abundance) and each with a different mass. 

Example:

A sample of bromine contains 53% bromine-79 and 47% bromine-81.

Relative atomic mass = ((53*79)+(47*81)/100 = 79.9

Relative atomic mass = (a*b)+(c*d) / 100