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✓ Correct
Answer: (D)
Solution
Reactivity in these two groups is governed by opposite tendencies. An alkali metal reacts by losing its single valence electron, and because the ionisation enthalpy falls down the group this becomes easier, so reactivity increases from top to bottom. A halogen reacts by gaining an electron, and as the atom grows larger down the group its pull on an incoming electron weakens, so reactivity decreases. The correct picture is thus that reactivity increases down the alkali metals but decreases down the halogens.
JEE Main · 2006 · 30 Apr 2006 · Offline · Single correct option