How does ionisation energy relate to electron configurations?

Ionisation energy is directly related to electron configurations as it measures the energy required to remove an electron from an atom.

Ionisation energy is a fundamental concept in chemistry that describes the amount of energy needed to remove an electron from a gaseous atom or ion. This energy is directly related to the electron configuration of the atom, which describes the distribution of electrons in an atom's atomic orbitals.

The electron configuration of an atom is determined by the principles of quantum mechanics. The electrons in an atom occupy energy levels, also known as shells, which are further divided into subshells. Each subshell is made up of orbitals, and each orbital can hold a maximum of two electrons. The energy of these orbitals increases as you move away from the nucleus, and within a shell, the energy of the orbitals also increases with the complexity of the subshell (s<p<d<f).

The first ionisation energy of an atom is the energy required to remove the most loosely held electron, which is typically the electron in the orbital with the highest energy. This is because these electrons are furthest from the nucleus and are therefore less attracted to the positive charge of the protons in the nucleus. As a result, they require less energy to be removed.

However, there are exceptions to this trend. For example, atoms with half-filled or fully filled subshells have slightly higher ionisation energies than expected. This is because these configurations are particularly stable, so it requires more energy to remove an electron from them.

In summary, the ionisation energy of an atom is directly related to its electron configuration. The energy required to remove an electron from an atom increases as you move closer to the nucleus and as you move from a filled to a half-filled subshell. Understanding this relationship is crucial for predicting the chemical behaviour of atoms and for understanding trends in the periodic table.