The ionization energy is the energy required to remove an electron from an atom. The more strongly the electrons are attracted to the nucleus, the more energy required to remove the electron. Therefore, ionization energy increases moving from left to right along a row and decreases moving down a column. In most cases, it is also possible to remove a second electron from an atom. The energy required to do this is called the second ionization energy. The second ionization energy is always higher than the first ionization energy. Ionization energies follow regular periodic trends. For example, removing one electron from a sodium atom in the IA group requires a relatively small amount of energy. Sodium likes to give up its electron to form ionic bonds leaving behind a more desirable octet of electrons. However, removing a second electron from sodium would disturb the now stable octet and require the atom to assume a less stable configuration. Removing the second electron is far more difficult than removing the first because of this fact. Elements in the IA group show a large increase between their first and second ionization energies.
