2.1.1

(a) isotopes as atoms of the same element with different numbers of neutrons and different masses

(b) atomic structure in terms of the numbers of protons, neutrons and electrons for atoms and ions, given the atomic number, mass number and any ionic charge

(c) explanation of the terms relative isotopic mass (mass compared with 1/12th mass of carbon-12) and relative atomic mass (weighted mean mass compared with 1/12th mass of carbon-12), based on the mass of a 12C atom, the standard for atomic masses

(e) use of the terms relative molecular mass, Mr, and relative formula mass and their calculation from relative atomic masses.

2.2.1

(a) the number of electrons that can fill the first four shells

(b) atomic orbitals, including:

(i) as a region around the nucleus that can hold up to two electrons, with opposite spins

(ii) the shapes of s- and p-orbitals

(iii) the number of orbitals making up s-, p- and d-sub-shells, and the number of electrons that can fill s-, p- and d-sub-shells

(c) filling of orbitals:

(i) for the first three shells and the 4s and 4p orbitals in order of increasing energy

(ii) for orbitals with the same energy, occupation singly before pairing