Question

Na, Mg and Al are the elements 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.(All India - 2012)

Answer 1

Answer:

sodium has largest atomic radius

Aluminum is least reactive

Answer 2

Element with largest atomic radius - Na or sodium.

Least reactive element - Al or aluminium.

Atomic radius decreases across the period in periodic table. This happens because number of electrons increases across the period, but number of shell remains constant.

Thus increase in electron with constant number of protons, increases the interaction and hence atomic radius decreases.

Reactivity decreases across the period for metals since interactions increases. As the pull of electron on proton increases, it requires more amount of energy to remove the electron, hence reactivity decreases.

The opposite is true for non metals. The reason for difference is metals react readily with losing electrons while non metals react with accepting electrons.