general terminology

unified atomic mass

one twelfth the mass of a carbon-12 atom…1.66×10^-27kg

relative atomic mass formula

average mass of atoms in sample of element/unified atomic mass unit

relative molecular mass formula

average mass of molecules in sample of molecular compound/unified atomic mass unit

water of crystallisation

number of moles of water associated with a crystal structure

hydrated compound

compound which contains a definite number of moles of water in their structure

anhydrous

containing no water of crystalisation

relative isotopic abundance

proportion of one particular isotope in a mixture of isotopes usually expressed as a percentage…heights of peaks in mass spectrum show proportion of each isotope present

molecular ion

ion that is formed by the loss of an electron from the original complete molecule during mass spectrometry…gives relative molecular mass of unknown compound