Na, Mg and Al are the elements of the same period of Modern Periodic Table having, one, two and three valence electrons respectively. Which of these elements (i) has the largest atomic radius, (ii) is least reactive? Justify your answer stating reason for each case.
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.
Solution
Given: Three elements Na, Mg and Al belonging to group 1, 2 and 13 respectively.
The electronic configurations of the three elements are as follows:
| Element Name | Symbol | Atomic Number | Electronic Configuration |
| Sodium | Na | 11 | 2,8,1 |
| Magnesium | Mg | 12 | 2,8,2 |
| Aluminium | Al | 13 | 2,8,3 |
(a) The element having the highest valence signifies the maximum number of electrons present in the valence shell of an atom. Hence, as per the electronic configurations, the element having highest valency is aluminium (Al).
(b) On going from left to right in the periodic table, atomic radius decreases due to increase in nuclear charge which pulls the outermost electron closer to the nucleus. Therefore, sodium has the largest atomic radius.
(c) On going from left to right in the periodic table, the reactivity decreases due to increased nuclear charge which makes the loss of outermost electron by the element difficult. Therefore, aluminium is the least reactive element.
