a)
₁₂A => 1s2 2s2 2p6 3s2 => grupa II-A, per. 3, val II
₁₅B => 1s2 2s2 2p6 3s2 3p3 => grupa 15 (V-A), per. 3, val III
₁₆C => 1s2 2s2 2p6 3s2 3p4 => grupa 16 (VI-A), per. 3, val II
₈D => 1s2 2s2 2p4 => grupa VI-A, per. 2, val II
₁₃E => 1s2 2s2 2p6 3s2 3p1 => grupa III-A, per. 3, val III
b)
formarea compusilor tinem seama de valentele identificate la a)
AC => AC
AD => AD
BD => B2D3
CD => CD
EC => E2C3
ED => E2D3
