Question

Na, Mg and Al are the elements of the 3rd period of the Modern Periodic Table having group number 1, 2 and 13 respectively. Which one of these elements has the (a) highest valency, (b) largest atomic radius, and (c) maximum chemical reactivity ? justify your answer stating the reason for each.

Answer 1

$\text{Sodium}\left(\text{Na}\right),\text{At. Number 11,}2,8,1$
$Magnesium\left(\text{Mg}\right),\text{At. Number 12,}2,8,2$
$Aluminium\left(\text{Al}\right),\text{At. Number 13,}2,8,3$
(a) Valency of Na is 1 as it will lose one electron to attain stable octet configuration.
The valency of Mg is 2 as it will lose two electrons to attain a stable octet configuration.
The valency of Al is 3 as it will lose three electrons to attain a stable octet configuration.
The element having the highest valency is Al, as it has 3 valence electrons.
(b) Period = No. of shells
So Na belongs to period-1, So Mg belongs to period-2, So Al belongs to period-3
The element with the largest atomic radius is Na as the left to right atomic radius decreases. Because across a period, electrons are added to the same shell, hence nuclear charge increases due to which size decreases.
(c) Across a period, the metallic character decreases as nuclear charge increases due to which losing electron becomes difficult.
Hence, The element with maximum chemical reactivity is Na as metallic character decreases from left to right.