Question

Arrange \[{\text{Li, Na, K, Rb, Cs}}\] in order of increasing electronegativity:
(A) \[{\text{Cs < Rb = K < Na < Li}}\]
(B) \[{\text{Rb < Cs = Li < Na < L}}\]
(C) \[{\text{Cs < Rb = Na < Li < K}}\]
(D) None of these

Answer 1

Hint: Electronegativity is a measure of an atom's tendency for attracting the bond pair of electrons towards itself. Determine how electronegativity varies when we go down the group.

Complete answer:
The chemical symbols \[{\text{Li, Na, K, Rb, Cs}}\] represents lithium, sodium, potassium, rubidium, cesium and francium respectively. These are alkali metals. They are present in the group 1A of the periodic table. They are highly electropositive metals and strong reducing agents. They have very low ionization enthalpy values.
On moving from top to bottom in a group the atomic radius increases as new electron shells are added. The distance between the outermost electron and the nucleus increases. Due to this, nucleus cannot easily attract electrons.
Due to this, on moving from top to bottom in a group the electronegativity values decrease.
Hence, when we move down from top to bottom in the group of alkali metals, the electronegativity values will decrease from lithium to cesium. Another way to say the same thing is that when we move down from bottom to top in the group of alkali metals, the electronegativity values will increase from cesium to lithium.
Write the decreasing order of electronegativities for alkali metals.
\[{\text{Cs < Rb = K < Na < Li}}\]

Hence, option (A) is the correct option.

Note: For alkali metals, on moving from top to bottom, the ionization energy decreases. Due to this, the reducing character increases from top to bottom. Lithium is the strongest reducing agent due to its greater hydration energy.