What elements have the highest ionisation energy ?

1. Ionisation energy is the quantity of energy needed to remove an electron from an atom.
2. The ionisation energy of an atom is directly proportional to the effective nuclear charge of an atom/ion.
3. Hence, ionisation increases left to right in a period and is observed to be highest for noble gases.
4. Noble gases are a stable system with a complete octet and hence will require the highest energy to remove an electron.
5. Example: Argon (Ar), Neon (Ne)
6. Therefore, noble gases will have the highest ionisation energy.