Boiled down to simple terms.
Atomic mass is the total of the number of protons and neutrons in an atom. It is measured in AMU (atomic mass units).
Atomic weight is how much 1 mole of the atoms of an element have. It is measured in grams.
Isotopes of an element have the same number of protons, but a different number of neutrons. It is like saying that a person has brothers/sisters. They are all siblings (isotopes) of a family (element).
For example, oxygen has an atomic mass of 15.9994 (round to 16), and an atomic number of 8. That means that the AVERAGE oxygen isotope (most abundant) has 8 protons (atomic number is 8) and 8 neutrons (16 protons + neutrons then subtract the number of protons). BUT there are other oxygen isotopes, they all have 8 protons, but they would have a different number (not 8) neutrons.
If I had 15.9994 (round to 16) grams of oxygen, there would be 1 mol of oxygen atoms, or 6.02x10^23 atoms present. Oxygen is not a good example because it is diatomic (O2), so really to get 1 mole of MOLECULES, you would need 31.9988 (round to 32) grams, and there would be 1.2x10^24 atoms.
Good luck
dsoz
