What is Ionization energy?
[[File:IonizationEnergyAtomicWeight.PNG|thumb|Ionization energy and [[Atomic number]]]] '''Ionization energy''' is the [[energy]] needed to remove the most loosely attached [[electron]] from an atom. The atom is not connected to any other atoms. The [[chemical element]]s to the left of the [[periodic table]] have a much lower ionization energy. The ones to the right have a much higher ionization energy. The [[chemical element]]s down the [[periodic table]] have a much lower ionization energy (due to electrons being farther away from the atom with increasing [[atomic radius]]). The ionization energy increases as each electron is removed. Ionization energies are dependent upon the'' atomic radius''. Since going from right to left on the periodic table, the atomic radius increases, and the ionization energy increases from left to right in the periods and up the groups. Exceptions to this trend is observed for [[Alkaline earth metal|alkaline earth metals]] (group 2) and nitrogen group elements (group 15). Typically, group 2 elements have ionization energy greater than [[group 13]] elements and [[Group 15 element|group 15]] elements have greater ionization energy than [[Group 16 element|group 16]] elements. Groups 2 and 15 have completely and half-filled [[Electron configuration|electronic configuration]] respectively, thus, it requires more energy to remove an electron from completely filled orbitals than incompletely filled orbitals. Alkali metals (IA group) have small ionization energies, especially when compared to [[Halogen|halogens]] or VII A group. In addition to the radius (distance between nucleus and the electrons in outermost orbital), the number of electrons between the nucleus and the electron(s) you're looking at in the outermost shell have an effect on the ionization energy as well. This effect, where the full positive charge of the nucleus is not felt by outer electrons due to the negative charges of inner electrons partially canceling out the positive charge, is called shielding. The more electrons