4. List the following ions is order of decreasing (largest to smallest) radius: $Ti^+$, $Sc^{3+}$, $Ca^{2+}$, $S^{2-}$, and $F^-$.
5. List in order of decreasing 1st ionization energy ($IE_1$): Na, Sr, K, Mg.
6. List in order of increasing 1st ionization energy ($IE_1$): Na, Li, P, Kr.
7. Explain why the ionization energy of nitrogen ($IE_1$ = 1402 kJ/mol) is lower than oxygen ($IE_1$ = 1314 kJ/mol) even though nitrogen is to the left of oxygen and doesn't follow the trend.