What is a molecule?
A group of atoms bonded together
What is the atomic number?
The number of protons in the nucleus of an atom
What is the mass number?
The total of the protons and neutrons (top number)
What is an isotope?
Different atomic forms of the same element which have the same number of protons but different numbers of electrons
What is the RFM/Ar?
The average mass of atoms of an element
Calculate Ar from isotopic abundances
Multiply mass of each isotope by its abundance. Add those together and divide by the sum of the abundances.
E.g.
(35 x 75) + (37 x 25) / (75+25) = 35.5