The relative atomic mass, Ar or RAM:

The average mass of an elements naturally occurring isotopes relative to the mass of an element of carbon-12.

A mole of a substance is the amount of substance that has the same number of particles as there are in exactly 12g of carbon-12.

The particles may be atoms, molecules, ions or even electrons. This number of particles is referred to as Avagadro's constant, L and is approximately 6 x 10²³ mol^-1.

The mass of one mole of a substance is often referred to as molar mass .

An instrument called a mass spectrometer is used to calculate relative atomic mass. The mass of individual isotopes and their abundance is found in order to calculate RAM..

The empirical formula of a compound shows the simplest whole-number ratio of the elements present.

The molecular formula shows the total number of atoms of each element present in the molecule.