Question

Is it easier or harder to remove an electron from an atom if it has a lower ionization energy?

Answer 1

Clearly it is easier to remove an electron with a lower ionization energy. We expend less energy.

Explanation:

We typically measure the ionization energies of (gaseous) atoms:

`"Atom(g)"+Deltararr"Atomic cation(g)"+"electron"`

When `Delta` is quoted in `kJ*mol^-1` this the `"first ionization enthalpy"`

Ionization energies typically INCREASE across a Period (looking at the Table from left to right), but DECREASE down a Group.

Why should this be so?