Question

Electropositive character for the elements of group 13 follows the order?
A) \[{\text{B > Al > Ga > In > Tl}}\]
B) \[{\text{B < Al < Ga < In < Tl}}\]
C) \[{\text{B < Al > Ga < In > TI}}\]
D) \[{\text{B < Al > Ga > In > Tl}}\]

Answer 1

Hint:Electropositive character represents the ease with which an atom can donate electrons to form cations. Consider the factors that affect the electropositive character of group 13 elements.

Complete answer:
The following factors affect the electropositive character of elements
1) metallic character
2) The atomic size
3) effective nuclear charge
4) ionization potential

In the modern periodic table, highly electropositive elements are present at the bottom left corner and the highly electronegative elements are present at the top right corner.

In the modern periodic table, alkali metals are highly electropositive elements. Caesium is the most electropositive element in the modern periodic table.

Group 13 elements include boron, aluminium, gallium, indium and thallium. The valence shell electronic configuration of group 13 elements is \[{\text{n}}{{\text{s}}_{\text{2}}}{\text{n}}{{\text{p}}_{\text{1}}}\] .
Boron has smaller size and high ionization potential value than aluminium. Hence, boron is less electropositive than aluminium.

On moving down the group, there is a gradual decrease in the electropositive character from gallium to thallium. This is due to the presence of extra d-electrons. The shielding effect of these d-electrons on the outer electrons is very small. Due to this the nucleus tightly holds the outermost electrons. This decreases the electropositive character.

Hence, the correct answer is the option (D) \[{\text{B < Al > Ga > In > Tl}}\].

Note:The metals are electropositive as they have very low values of ionization potential. Non-metals are electronegative as they have very high values of ionization potential.