Question

Which of the following pair of elements/ions has a larger atomic/ionic radius? Explain

(F,Br) (Al3+, Na+)

Answer 1

1. (F, Br) :

Fluorine (F) and Bromine (Br) belongs to group 17 in period table. Fluorine is at the top of the group while bromine is below it.

As going down along every group in period table, atomic/ionic radius decreases.

• Since bromine is located below the fluorine, bromine has a larger atomic radius.

2. (Al³⁺, Na⁺) :

Al³⁺ and Na⁺ are isoelectronic species, meaning that they have the same no.of electrons ( = 10 electrons).

But no.of protons are different. Al³⁺ has 13 protons while Na⁺ has only 11 protons.

Hence, Electrostatic attraction in Al³⁺ ion will be higher and hence Al³⁺ will have a lower ionic radius.

• Hence, Na⁺ has a larger ionic radius.