Period 3 (Na to Ar) illustrates all periodic trends clearly. Atomic radius (pm): Na(186) > Mg(160) > Al(143) > Si(117) > P(110) > S(104) > Cl(99) > Ar(-). IE1 $\frac{kJ}{mol}$: Na(496) < Mg(738) < Al(577*) < Si(786) < P(1012) < S(1000*) < Cl(1251) < Ar(1521). *Note exceptions: Al < Mg and S < P. EN (Pauling): Na(0.9) < Mg(1.2) < Al(1.5) < Si(1.8) < P(2.1) < S(2.5) < Cl(3.0) < Ar(-). Oxide character: Na2O and MgO are basic; Al2O3 is amphoteric; SiO2, P4O10, SO3, Cl2O7 are acidic (increasing acidity).