Question

Why do halogens have very high ionisation energies?

Answer 1

1. Halogens have a very small atomic size, which means their valence electrons are close to the nucleus.
2. They experience a high effective nuclear charge, which strongly attracts the valence electrons towards the nucleus.
3. As a result, a lot of energy is required to remove an electron from a halogen atom.
4. Fluorine, being the smallest halogen atom, has the highest ionisation energy.
5. Ionisation energies decrease down the group due to increasing atomic size and decreasing effective nuclear charge.