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

Nov 3, 2016

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:

$\text{Atom(g)"+Deltararr"Atomic cation(g)"+"electron}$

When $\Delta$ is quoted in $k J \cdot m o {l}^{-} 1$ this the $\text{first ionization enthalpy}$

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?