2.6 Ionization Energy

This topic explains ionization energy, its periodic trends, the factors that influence it, and how it can be used to deduce the position of an element in the periodic table and its electronic configuration.

Definition

Ionization Energy (I.E.): The minimum energy needed to remove the outermost electron (the most loosely bonded electron) from a gaseous, isolated atom.

Main Idea

Ionization energy is the energy required to remove an electron from a gaseous atom. It generally increases across a period and decreases down a group, with some exceptions. The trends are influenced by nuclear charge, atomic radius, shielding effect, and spin-pair repulsion. Successive ionization energies can be used to deduce the group of an element and its electronic configuration.

Core Concept

Ionization energy is a measure of how strongly an atom holds onto its outermost electron. The stronger the attraction between the nucleus and the outer electron, the higher the ionization energy.

Example: Na_{(g)} \rightarrow Na^+_{(g)} + 1e^- \quad I.E = 496 \text{ kJ/mol} Mg_{(g)} \rightarrow Mg^+_{(g)} + 1e^- \quad I.E = 738 \text{ kJ/mol}

The atom must be in the gaseous state to avoid the influence of other factors like heat of fusion, bond dissociation energy, and heat of vaporization.