Question

Which of the following pairs of ions are isoelectronic and isostructural ?

• A. ${ SO_3^{2-} , NO^-_3 }$
• B. ${ ClO_3^- , SO_3^{2-} }$
• C. ${CO_3^{2-} , SO_3^{2-} }$
• D. ${ ClO^-_3 , CO_3^{2-}}$

Answer 1

The Correct Option is B

To determine which pairs of ions are isoelectronic and isostructural, we need to understand these terms:

1. Isoelectronic: Ions or atoms that have the same number of electrons. This means that after accounting for the charges, the total electron count is the same.
2. Isostructural: Ions or compounds that have the same shape or geometry.

Let's analyze each option:

1. ${ SO_3^{2-} } and ${ NO_3^- }:
   • ${ SO_3^{2-} }: Sulfur has 16 electrons, oxygen has 8 electrons each. Total electrons = 16 + 3(8) + 2 = 34.
   • ${ NO_3^- }: Nitrogen has 7 electrons, oxygen has 8 electrons each. Total electrons = 7 + 3(8) + 1 = 32.
     They are not isoelectronic.
2. ${ ClO_3^- } and ${ SO_3^{2-} }:
   • ${ ClO_3^- }: Chlorine has 17 electrons, oxygen has 8 electrons each. Total electrons = 17 + 3(8) + 1 = 34.
   • ${ SO_3^{2- }: As calculated before, total electrons = 34.
     They are isoelectronic.
   • Both ions have a similar tetrahedral geometry due to the presence of three oxygen atoms bonded to a central atom.
3. ${ CO_3^{2-} } and ${ SO_3^{2-} }:
   • ${ CO_3^{2-} }: Carbon has 6 electrons, oxygen has 8 electrons each. Total electrons = 6 + 3(8) + 2 = 32.
   • Since ${ CO_3^{2-} } differs in electron count, they are not isoelectronic.
4. ${ ClO^-_3 } and ${ CO_3^{2-} }:
   • As calculated earlier, both have different electron counts (34 vs 32).
   • They are not isoelectronic, nor are they structurally similar.

By analyzing the options, we conclude that the correct pair is:

• ${ ClO_3^- } and ${ SO_3^{2-} } are both isoelectronic (34 electrons each) and isostructural (similar geometric arrangements).