Question

The ion that is isoelectronic with CO is:
A.${\text{N}}_{\text{2}}^{\text{ + }}$
B.${\text{C}}{{\text{N}}^{\text{ - }}}$
C.${\text{O}}_{\text{2}}^{\text{ + }}$
D.${\text{O}}_{\text{2}}^{\text{ - }}$

Answer 1

Hint:Isoelectronic species: Elements, atoms, or ions that have the same number of electrons are said to be isoelectronic species. For example, ${{\text{O}}^{{\text{2 - }}}}$, ${{\text{F}}^{\text{ - }}}$, both have 10 electrons and thus are isoelectronic species.
Complete step by step answer:
CO has 14 electrons in total, 6 electrons from carbon and 8 from oxygen.
${\text{N}}_{\text{2}}^{\text{ + }}$: there are 12 electrons in ${\text{N}}_{\text{2}}^{\text{ + }}$, 7 from each nitrogen atom and since there is a 2+ charge, it means it has lost 2 electrons out of 14 and thus 12 electrons in total
 ${\text{C}}{{\text{N}}^{\text{ - }}}$: 6 electrons from carbon, 7 from nitrogen and 1 extra electron since it has a negative charge. Thus having a total of 14 electrons.
${\text{O}}_{\text{2}}^{\text{ + }}$: 8 electrons from each oxygen atom giving a total of 16 electrons but since it is bearing a positive charge of 1. It has a total of 15 electrons.
${\text{O}}_{\text{2}}^{\text{ - }}$: 8 electrons from each oxygen atom and one extra electron due to a negative charge, giving a total of 17 electrons.
From the above calculations, it is clear that both CO and ${\text{C}}{{\text{N}}^{\text{ - }}}$ have 14 electrons each and thus have same number of electrons. Therefore, they are isoelectronic.

Hence, option B is the correct answer.

Note: The importance of the concept of isoelectronic species lies in identifying significantly related species (in terms of the number of electrons) as pairs or series. Isoelectronic species can be expected to show useful consistency and predictability in their properties. The term isoelectronic species differ from isotopes, isobars. The isotopes are defined as atoms having the same atomic number but different atomic mass whereas isobars are the atoms with the same atomic mass value but different atomic number.