Question

Elements with very large ionization energies also tend to have highly exothermic electron affinities. Explain. Which group of elements would you expect to be an exception to this statement?

Short answer

Elements with large ionization energies also have highly exothermic electron affinities because both properties are influenced by the effective nuclear charge and the distance between the nucleus and outermost electrons. The stronger the nuclear attraction for electrons, the higher the ionization energy and electron affinity. However, Group 18 elements, the noble gases, are an exception to this statement. They have large ionization energies due to their full electron configurations but low electron affinities, as their full electron shells make them less likely to gain additional electrons.

Step-by-step solution

Understanding Ionization Energy

Ionization energy is the amount of energy required to remove an electron from a neutral gaseous atom. It generally increases across a period and decreases down a group in the periodic table. Elements with high ionization energies have stronger attractions between the nucleus and the electrons, making it more difficult to remove an electron from these elements.

Understanding Electron Affinity

Electron affinity is the amount of energy released when an electron is added to a neutral gaseous atom, forming a negative ion. Elements with high electron affinities tend to release more energy when gaining an electron, which makes them more likely to attract an electron. Electron affinity generally increases across a period and decreases down a group in the periodic table.

Relationship between Ionization Energy and Electron Affinity

Both ionization energy and electron affinity are influenced by the same factors - the effective nuclear charge and the distance between the nucleus and the outermost electrons. The more significant the effective nuclear charge or the smaller the distance between the nucleus and the electron, the higher the ionization energy and electron affinity. Consequently, elements with large ionization energies will have highly exothermic electron affinities because in both cases, the strong nuclear attraction for electrons is responsible.

Identifying an Exceptional Group in the Periodic Table

Elements in Group 18 of the periodic table, the noble gases, are potential exceptions to the statement that elements with large ionization energies also have highly exothermic electron affinities. The noble gases have full electron configurations and high ionization energies due to the strong attraction between the nucleus and the electrons in their completely filled energy levels. However, their electron affinities are generally low (not highly exothermic) since their full electron shells make them relatively unreactive and unlikely to gain additional electrons.