\({R^ + }:3{s^2}3{p^6} \to R:1{s^2}2{{\rm{s}}^2}2{p^6}3{{\rm{s}}^2}3{p^6}4{{\rm{s}}^1}:STT = Z = 19\left( K \right)\), chu kỳ 4 nhóm IA
\({Y^{2 + }}:3{s^2}3{p^6} \to Y:1{s^2}2{{\rm{s}}^2}2{p^6}3{{\rm{s}}^2}3{p^6}4{{\rm{s}}^2}:STT = Z = 20\left( {Ca} \right)\), chu kỳ 4, nhóm IIA
\({X^ - }:3{s^2}3{p^6} \to X:1{s^2}2{{\rm{s}}^2}2{p^6}3{{\rm{s}}^2}3{p^5}:STT = Z = 17\left( {Cl} \right)\), chu kỳ 3 nhóm VIIA
