RAM and RFM

RAM

RAM stands for Relative Atomic Mass.

It is used when discussing the mass of an atom.

Exam definition:

The weighted average mass of an atom compared to $\frac{1}{12}$ of the mass of an atom of carbon-12.

RFM

RFM stands for Relative Formula Mass.

It is used when discussing the mass of a molecule or ionic compound.

Also known as relative molecular mass (MMR), Mr, and molecular mass.

It is calculated as mass number x number of the atom in the substance. E.g. the RFM of water (H₂O)

= ((the mass number of) H x 2) + ((the mass number of) O x 1)

= (1 × 2) + (16 × 1)

= 2 + 16

= 18