The electron affinities, in kJ>mol, for the group 11 and group 12 metals are as follows: Cu -119 Zn 7 0 Ag -126 Cd 7 0 Au -223 Hg 7 0 (b) Why do the electron affinities of the group 11 elements become more negative as we move down the group? [Hint: Examine the trends in the electron affinities of other groups as we proceed down the periodic table.]

Key Concepts

Electron Affinity

Electron affinity is the energy change that occurs when an electron is added to a neutral atom in the gas phase. It is typically expressed in kilojoules per mole (kJ/mol). A more negative electron affinity indicates a greater tendency for an atom to gain an electron, which is often influenced by the atom's electronic structure and the effective nuclear charge experienced by the added electron.

Periodic Trends

Periodic trends refer to the predictable patterns observed in the properties of elements as one moves across or down the periodic table. For electron affinity, trends generally show that electron affinity becomes more negative across a period due to increasing nuclear charge, while it can vary down a group due to changes in atomic size and shielding effects, which affect the attraction between the nucleus and the added electron.

Group 11 and Group 12 Elements

Group 11 elements (Cu, Ag, Au) are known as coinage metals and typically exhibit higher electron affinities compared to Group 12 elements (Zn, Cd, Hg). The electron affinities of Group 11 elements become more negative down the group due to increased atomic size and decreased effective nuclear charge, which allows for a more favorable energy change when gaining an electron, contrasting with the relatively stable electron configurations of Group 12 elements.