How do you account for the fact that, although potassium is placed after argon in the periodic table,

it has a lower relative atomic mass? What is the evidence that the aufbau principle is only approximately true? The first list in the table opposite contains symbols or phrases, each of which has a ‘partner’ in the second list. Match the ‘partners’; there is only one match for each pair of symbols or phrases.

Suggest explanations for the following. (a) High values of ionization energies are associated with the noble gases. (b) The enthalpy changes associated with the attachment of the first and second electrons to an O atom are exothermic and endothermic, respectively. (c) In an Li atom in its ground state, the outer electron occupies a 2s rather than a 2p orbital.