Q55E - Chemistry (OpenStax)

Question

What is the molecular structure about the nitrogen atom in trimethyl amine and in the trimethyl ammonium ion, \({\left( {C{H_3}} \right)_3}N{H^ + }\)? What is the hybridization of the nitrogen atom in trimethyl amine and in the trimethyl ammonium ion?

Step-by-Step Solution

Answer

By forming a cation, hybridization does not change, but molecular geometry changes.

Step 1: Amines

Amines are generally neutral molecules if nitrogen shares 3 bonds and has lone pair.

If that's not the case, and it has 4 bonds around it, then it becomes positively charged.

By forming a \({4^{th }}\)bond hybridization, the molecular geometry changes but not the hybridization.

Step 2: The trimethylamine

Let's observe trimethylamine.

This compound has 3 methyl groups directly bonded to nitrogen atoms, as seen in the picture.

Also, nitrogen contains a lone pair of electrons.

Because of its lone pair, this molecule cannot take a planar configuration.

Instead, it takes a trigonal pyramidal structure with a bond angle around \(10{7^\circ }.\) 

               Trimethyl amine

Step 3: The hybridization

The hybridization is interesting.

The nitrogen atom here has 3 single bonds, but the lone electron pair also has an impact.

When it's present, in terms of determining hybridization, the lone pair is considered a "single bond."

Therefore, if it has "4 single bonds," its hybridization is \(s{p^3}.\) 

Step 4: The trimethylammonium ion

Let's observe trimethylammonium ion.

This compound has 3 methyl groups directly bonded to the nitrogen atom, as seen in the picture.

Also, nitrogen contains one H atom, which makes this compound positively charged.

4 single bonds around an atom indicate a tetrahedral arrangement of atoms and bonds.

Step 5: Hybridization

The nitrogen atom here has 4 single bonds.

Therefore, if it has "4 single bonds," its hybridization is \(s{p^3}\).