what is chemical reactivity ...?
and why does it first decrease and then increase as we move from left to right in a period?
and why does it increase in metals as we go down a grup and decrease in non metals as we go down a group?
Dear Student,
The chemical reactivity is defined as the tendency of a compound to undergo chemical changes.
The elements with octet configuration are the most stable.
Along a period, the alkali metals and halogens are the most reactive. This is due to the fact that alkali metals can easily lose one electron to form a cation with noble gas configuration.
Similarly, the halogens need only one electron to obtain stability.
Thus, as we move along a period the tendency to lose electron decreases for the metals and tendency to gain electron increases for the non-metals. Consequently, the reactivity first decreases then increases.
As we go down a group in metals, the atomic size goes on increasing, nuclear charge decreases, thus the tendency to lose electrons increases and consequently reactivity increases.
As we move down a group in halogens, the size increase, nuclear charge decreases thus the tendency to gain electron decreases and consequently the reactivity decreases.
Hope this helps.
Cheers!