Answer
Ionization energy is the amount of energy required to remove an electron from an atom. In alkali metals, the outer energy level has one electron. Removing this electron is fairly easy, because removing it yields a completely filled energy level (an octet), and thus stability. However, removing a second electron turns very complicated. Now that the atom has achieved stability and a full octet, the electrons are not as "loose," this taking a lot of energy to remove it. Furthermore, without the first electron, a cation was formed. This ion has a positive charge, and so it attracts the negatively charged electrons with an even greater force. This is why there is a large increase between the first and second ionization energies of alkali metals.
Work Step by Step
Ionization energy is the amount of energy required to remove an electron from an atom. In alkali metals, the outer energy level has one electron. Removing this electron is fairly easy, because removing it yields a completely filled energy level (an octet), and thus stability. However, removing a second electron turns very complicated. Now that the atom has achieved stability and a full octet, the electrons are not as "loose," this taking a lot of energy to remove it. Furthermore, without the first electron, a cation was formed. This ion has a positive charge, and so it attracts the negatively charged electrons with an even greater force. This is why there is a large increase between the first and second ionization energies of alkali metals.
