Question

How many of the following have 10 electrons: O2-, O, Al3+, Al, F, F-, Mg2+, Mg, N-3

Answer 1

Correct answer is 5 (O2-, Al3+, F-, Mg2+, N-3).

A negative sign means more of electrons and a positive sign means a lack of electrons.

Here N3− with atomic no. 7 has 7+3= 10 electrons

O2− with atomic no. 8 has 8+2 = 10 electrons

F− with atomic no. 9 has 9+1= 10 electrons

Na+ with atomic no. 11 has 9-1= 10 electrons

Mg2+ with atomic no. 12 has 12-2= 10 electrons

Al3+ with atomic no. 13 has 13-3= 10 electrons

Since all these ions have 10 electrons in their shell, therefore, these are iso-electronic species

The more + the charge, the smaller the ionic radius. Remember that - means adding electrons.

These electrons go in the outermost shells.