Question

Explain why BH3 is trigonal planar and NH3 is trigonal pyramidal.

Answer 1

BH3 is trigonal planar because of three bonded atoms, while NH3 is trigonal pyramidal due to one lone pair of electrons on the central nitrogen atom.

Step-by-step explanation:

The molecular geometry of BH3 is trigonal planar because it has three bonded atoms and no lone pairs of electrons. In a trigonal planar structure, the three atoms lie in the same plane, with bond angles of 120° between them. An example of a molecule with a trigonal planar structure is BF3.

On the other hand, the molecular geometry of NH3 is trigonal pyramidal. This is because NH3 has three bonded atoms and one lone pair of electrons on the central nitrogen atom. The three hydrogen atoms are arranged in a three-dimensional pyramid shape, with bond angles slightly smaller than 109.5° due to repulsion between the lone pair and the bonding pairs of electrons.

Answer 2

Answer:o It is important to realise that mixing will be small unless there are electrons in the 4a1 LUMO, this is why NH3 is pyramidal while BH3 is planar! ... This mixing is very strong and stabilises the 3a1 MO substantially and hence NH3 is trigonal pyramidal and not planar.

Step-by-step explanation: