Describe the periodic trends in the valence of elements with respect to their oxides and hydrides.

The valence of representative elements with respect to hydrogen and oxygen exhibits periodic trends across a period and down a group.
$1$. Valence with respect to hydrogen: It increases from $1$ to $4$ for groups $1$ to $14$ and then decreases from $4$ to $1$ for groups $14$ to $17$.
$2$. Valence with respect to oxygen: It generally increases from $1$ to $7$ across a period (equal to the group number for groups $1-13$ and $8$ minus the group number for groups $14-17$).

Group	$1$ to $13$	$14$	$15$	$16$	$17$
Formula of Hydride	$MH$ to $MH_3$	$MH_4$	$MH_3$	$MH_2$	$MH$
Formula of Oxide	$M_2O$ to $M_2O_3$	$MO_2$	$M_2O_5$	$MO_3$	$M_2O_7$