A-level Chemistry Definitions questions and answers well illustrated.

sotopes - ANS.atoms of the same element with different numbers of neutrons atomic (proton) number - ANS.the number of protons in the nucleus of an atom mass (nucleon) number - ANS.the number of particles (protons and neutrons) in the nucleus ion - ANS.a positively or negatively charged atom or (covalently bonded) group of atoms (molecular ion) relative isotopic mass - ANS.the mass of an atom of an isotope compared with one twelfth of the mass of an atom of carbon-12 relative atomic mass - ANS.the weighted mean mass of an an atom of an element compared with one twelfth of the mass of an atom of carbon-12 relative molecular mass (Mr) - ANS.the weighted mean mass of a molecule compared with one twelfth of the mass of an atom of carbon-12 relative formula mass - ANS.is the weighted mean mass of a formula unit compared with one twelfth of the mass of an atom of carbon-12 amount of substance - ANS.the quantity whose unit is the mole: chemists use 'amount of substance' as a means of counting atom