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Ionization energy is the energy required to remove an electron from an atom or ion in its gaseous state. Electron affinity, on the other hand, is the energy released when an electron is added to a neutral atom or ion in its gaseous state. Both of these properties are influenced by the size of the atom, the nuclear charge, and the electron configuration.

Atomic size generally affects both ionization energy and electron affinity. As you move across a period from left to right, the atomic size decreases due to increasing nuclear charge, which pulls the electrons closer to the nucleus. This makes it harder to remove an electron (higher ionization energy) and easier to add an electron (higher electron affinity).

The number of protons in the nucleus (also known as the atomic number) increases as we move across the periodic table from left to right. The increase in nuclear charge increases the attraction between the nucleus and the electrons. This leads to an increase in ionization energy because more energy is required to remove an electron from an atom with a larger nuclear charge and thus opposing the trend in electron affinity.

Electron configuration refers to the arrangement of electrons in orbitals around the nucleus. When an element has a half-filled or fully-filled orbital, it exhibits greater stability. As a result, atoms with half-filled or fully-filled orbitals tend to have higher ionization energies and lower electron affinities due to the increased stability these configurations provide.

The opposing trends in ionization energies and electron affinities can be attributed to the combined effects of atomic size, nuclear charge, and electron configuration. As you move across a period in the periodic table, the atomic size decreases and the nuclear charge increases, making it more challenging to remove an electron but easier to add one. The electron configurations in certain elements can cause deviations in these trends, especially when there are atoms with half-filled or fully-filled orbitals. The stability of these configurations can provide higher ionization energies and lower electron affinities. In summary, ionization energy tends to increase across the second row of the periodic table due to the decrease in atomic size and increase in nuclear charge, while electron affinity generally decreases due to the effects of atomic size, nuclear charge, and electron configuration in certain elements with half-filled or fully-filled orbitals.