Q.State the valency shown by elements of Group 1, Group 16 and Group 17 of the periodic table, and explain how the group valency of a representative element is generally related to the number of valence electrons.

For main-group elements, valency (the number of chemical bonds an atom typically forms) usually equals either the number of valence electrons directly, or the difference between 8 and that number — whichever value is actually observed in real compounds. Group 1 (1 valence electron) shows valency 1; group 2 shows valency 2; group 13 shows valency 3; group 14 shows valency 4; group 15 shows both 3 and 5 (5 valence electrons, or 8−5=3); group 16 shows both 2 and 6; group 17 shows both 1 and 7; group 18 shows valency 0. This pattern is directly visible in the formulas of hydrides and oxides across a period (e.g. LiH, BeH2, B2H6, CH4, NH3, H2 …