Chemistry Review: The Structure Of Atoms

Atoms of the same element all have the same number of Protons. That number is called the Atomic Number .

                            
Isotopes are Atoms of an element with different numbers of neutrons. That means that they have different Mass Numbers . Mass number is the sum of the numbers of protons and neutrons in the nucleus of an atom.

There's so many atoms that the average atoms mass of chlorine represents the average of all chlorine atoms on Earth.

                 
Avogardro's number used of molecules in one Mole.