Q56E - Chemistry (OpenStax)

Question

Carbon forms the \({\rm{CO}}_{\rm{3}}^{{\rm{2 - }}}\)ion, yet silicon does not form an analogous \({\rm{SiO}}_{\rm{3}}^{{\rm{2 - }}}\)ion. Why?

Step-by-Step Solution

Answer

A silicon atom is significantly larger than an oxygen atom, the double bond of oxygen cannot be stable and so silicon does not exist in the form of  \({\rm{SiO}}_3^{2 - }.\)

Step 1: Lewis structure of carbonate ion

The Lewis structure of a carbonate ion has two single bonds, two negative oxygen atoms, and one short double bond to neutral oxygen.

Lewis structure of carbonate ion

Step 2: Explanation

A carbon atom is similar in size as compared to an oxygen atom, while a silicon atom is larger.

 

Since carbon is smaller in size, it can form an ion with three oxygen atoms because of its ability to make a double bond with oxygen. This structure is, however, incompatible with the carbonate ion's observed symmetry, which implies that the three bonds and oxygen atoms are equivalent.

 

A silicon atom is significantly larger than an oxygen atom, and the double bond of oxygen cannot be stable in this case.