Q.Name the first element of groups 16, 17 and 18.

Group 16, the oxygen family (O, S, Se, Te, Po), has the general valence-shell configuration ns2np4 and is also called the chalcogens, since a large number of metal ores are oxides or sulfides. Oxygen is the most abundant element on Earth (about 21% of air by volume, 47% of the crust by mass); sulfur occurs mainly as sulfates (gypsum, Epsom salt, baryte) and sulfides (galena, zinc blende, copper pyrites); selenium and tellurium occur as metal selenides/tellurides; polonium is a radioactive decay product of thorium/uranium. Down the group, atomic and ionic radii increase, ionisation enthalpy decreases, and electronegativity decreases, all because each successive element adds a new outer shell. Electron gain enthalpy becomes less negative down the group overall, but oxygen is an exception, showing a LESS negative value than sulfur, because oxygen's small, compact 2p orbitals suffer strong electron-electron repulsion when a …