Question

how many pairs of bonding electrons are present in a molecule that displays a trigonal bipyramidal molecular shape?
3
6
5
4

Explanation:

Step1: Recall VSEPR theory

The trigonal bipyramidal molecular shape is determined by the number of bonding electron pairs (and lone pairs) around the central atom. For a trigonal bipyramidal shape, the electron - pair geometry (and molecular shape, assuming no lone pairs on the central atom) is associated with 5 bonding electron pairs. This is because the trigonal bipyramidal geometry has 5 regions of electron density, which in the case of only bonding pairs (no lone pairs) corresponds to 5 bonding electron pairs. For example, in a molecule like \(PCl_5\), the central phosphorus atom has 5 bonding pairs (each with a chlorine atom), and the molecular shape is trigonal bipyramidal.

Step2: Evaluate the options

• Option 3: A molecular shape with 3 bonding pairs would be trigonal planar (e.g., \(BF_3\)), so this is incorrect.
• Option 6: A molecular shape with 6 bonding pairs would be octahedral (e.g., \(SF_6\)), so this is incorrect.
• Option 5: As we recalled from VSEPR theory, a trigonal bipyramidal molecular shape is associated with 5 bonding electron pairs, so this is correct.
• Option 4: A molecular shape with 4 bonding pairs would be tetrahedral (e.g., \(CH_4\)) or see - saw (if there is a lone pair), so this is incorrect.

Answer:

5 (the option with "5")