Why is the second ionization energy greater than the first ionization energy?

a. it is more difficult to remove a second electron from an atom

b. the size of atoms increases down a group

c. the size of anions decreases across a period

d. the nuclear attraction from protons in the nucleus decreases

Answer is: a. it is more difficult to remove a second electron from an atom.

The ionization energy (Ei) is the minimum amount of energy required to remove the valence electron, when element lose electrons, oxidation number of element grows (oxidation process).

For example, sodium has the larger second than first ionization energy, because when it lost one electron (first ionization energy), it has stable electron configuration of noble gas neon (1s²2s²2p⁶), so sodium does not need to lost second electron, because it will have unstable electron configuration.

The correct answer is option A. It is more difficult to remove a second electron from an atom.

First ionization energy is the energy required to remove one electron from a neutral atom. However, second ionization energy is the energy required to remove from a + 1 cation, as the atom has already lost an electron.

In a + 1 cation the number of proton is greater than the electron, so the nuclear attraction from protons in the nucleus increases. As a result valence shell electrons are more tightly held. So it always requires more energy to remove an electron from a + 1 cation than from a neutral atom.