91Ó°ÊÓ

Compare both the numbers of protons and electrons present in each to rank the following ions in order of

increasing radius:\({\bf{A}}{{\bf{s}}^{{\bf{3}}--}},{\rm{ }}{\bf{B}}{{\bf{r}}^--},{\rm{ }}{{\bf{K}}^ + },{\rm{ }}{\bf{M}}{{\bf{g}}^{{\bf{2}} + }}\).

The ionic radii of the ions \({{\bf{S}}^{{\bf{2}}-}},{\rm{ }}{\bf{C}}{{\bf{l}}^-},{\rm{ }}{\bf{and}}{\rm{ }}{{\bf{K}}^ + }\) are 184, 181, 138 pm respectively. Explain why these ions havedifferent sizes even though they contain the same number of electrons.

Which main group atom would be expected to have the lowest second ionization energy?

Explain why Al is a member of group 13 rather than group 3?