Ionisation Energies

“Ionisation Energies”

• Ionisation energy is defined as the amount of energy required to remove an electron from an isolated atom or molecule in a gaseous state, creating a positive ion.
• The process usually involves one or more ionisation energies, where each corresponds to the removal of one electron.
• The 1st ionisation energy applies to the removal of the first electron, the 2nd ionisation energy refers to the removal of the second electron, and so on.
• As electrons are removed, it becomes increasingly hard to remove the next electron. Therefore, Ionisation energies increase progressively.
• Alkali metals, located in the first group of the periodic table, have the lowest first ionisation energies as they have a single electron in their outermost energy level.
• Noble gases, occupying the last group of the periodic table, have the highest first ionisation energies due to full electron configurations in their outermost energy levels.
• The general trend across a period from left to right is an increase in first ionisation energy. This is due to increasing nuclear charge and decreasing atomic radius.
• There are exceptions to this trend due to electron shielding and sub-level electron pairing.
• Within a group from top to bottom, first ionisation energy decreases. This is because the electrons are further from the nucleus and there’s also increased shielding from the inner electron shells.
• Ionisation energies provide evidence for the arrangement of electrons in energy levels, sub-levels, and orbitals.
• Ionisation energies can be used to predict the reactivity of elements. Elements with low first ionisation energies are typically more reactive than those with high first ionisation energies.

Understanding and recognising the trends and patterns in ionisation energies is crucial for predicting the properties of elements and their compounds.