Question

Following statements regarding the periodic trends of chemical reactivity of the alkali metals and the halogens are given. Which of these statements gives the correct picture? 

(a) The reactivity decreases in the alkali metals but increases in the halogens with increase in atomic number down the group 

(b) In both the alkali metals and the halogens the chemical reactivity decreases with increase in atomic number down the group 

(c) Chemical reactivity increases with increase in atomic number down the group in both the alkali metals and halogens 

(d) In alkali metals the reactivity increases but in the halogens it decreases with increase in atomic number down the group.

Answer 1

(d) : All the alkali metals are highly reactive elements since they have a strong tendency to lose the single valence s-electron to form unipositive ions having inert gas configuration. This reactivity arises due to their low ionization enthalpies and high negative values of their standard electrode potentials. 

However, the reactivity of halogens decreases with increase in atomic number due to following reasons: 

(a) As the size increases, the attraction for an additional electron by the nucleus becomes less. 

(b) Due to decrease in electronegativity from F to I, the bond between halogen and other elements becomes weaker and weaker.