What is Ionization potential?

Ionization potential can be defined as the amount of energy needed to remove one or more electrons from the outermost shell of the isolated atom in gaseous state. Ionization potential can be measured as the minimum potential required removing the loosely held electron from the rest of the atom. It can be measured in the unit electron volts. Ionization is the process in which the neutral atom or molecule gains or losses electrons and therefore acquires a positive or negative electrical charge. The energy per unit charge required to remove an electron from the given kind of atom or molecule to the infinite distance. The potential difference through which a bound electron should be raised to free it from the atom or molecule to which it is attached. Particularly, the ionization potential is the difference in potential among the initial state, in which the electron is bound, and the final state, in which it is at rest at infinity. The electron is held in the atom by electrostatic force of the positively charged protons in nucleus and negative charge of the electrons. By supplying sufficient energy, it is possible to remove an electron from an atom. The element is first brought into the vapour state. Then the electron is removed by supplying energy equivalent to ionization potential. Metals have low ionization potential usually whereas non-metals have high ionization potential.

Metalloids posses intermediate ionization potential. The inert gases have very high ionization potential, because of the stability of the outer shell. Ionization potential rises across the period due to increase in nuclear charge due to which the atomic size decreases. Therefore, more energy is needed to pull away the electron from outermost shell of the atom of smaller size. The ionization potential decreases down the group due to increase in the number of shells. The effective nuclear charge decreases as the atomic size increases. Therefore it is easier to pull 1 electron from the outermost shell of the atom.