In a molecule with a trigonal pyramidal shape, how many outer atoms and lone pairs are present around the central atom?

• A. 3 outer atoms and 1 lone pair
• B. 2 outer atoms and 2 lone pairs
• C. 4 outer atoms and 0 lone pairs
• D. 3 outer atoms and 2 lone pairs

Answer: (A)

Verified step by step guidance

1. Recall that the molecular shape called trigonal pyramidal is derived from a tetrahedral electron geometry where one of the positions is occupied by a lone pair instead of an atom.
2. In a trigonal pyramidal molecule, the central atom is bonded to three outer atoms, which form the base of the pyramid.
3. Since the electron geometry is tetrahedral, there are four regions of electron density around the central atom; three are bonding pairs (outer atoms) and one is a lone pair.
4. The lone pair occupies one of the four positions, causing the shape to be trigonal pyramidal rather than tetrahedral.
5. Therefore, the central atom in a trigonal pyramidal molecule has 3 outer atoms bonded to it and 1 lone pair of electrons.