Which molecule has trigonal bipyramidal geometry?

Which molecule has trigonal bipyramidal geometry?

• A. PF5
• B. SF6
• C. CH4
• D. NH3

Answer: (A)

Think about how VSEPR shapes form from the number of electron pairs around the central atom. Five regions of electron density arrange themselves in a trigonal bipyramidal pattern: three positions form a plane at about 120°, and two positions sit along the axis above and below at about 90° to the plane. PF5 has exactly five bonding pairs and no lone pairs, so it fits this five-domain scenario and adopts a trigonal bipyramidal geometry. Other molecules here don’t match that arrangement: sulfur hexafluoride has six electron pairs leading to an octahedral shape; methane has four electron pairs giving a tetrahedral shape; ammonia has four electron domains but one is a lone pair, giving a trigonal pyramidal shape rather than trigonal bipyramidal.

Think about how VSEPR shapes form from the number of electron pairs around the central atom. Five regions of electron density arrange themselves in a trigonal bipyramidal pattern: three positions form a plane at about 120°, and two positions sit along the axis above and below at about 90° to the plane.

PF5 has exactly five bonding pairs and no lone pairs, so it fits this five-domain scenario and adopts a trigonal bipyramidal geometry. Other molecules here don’t match that arrangement: sulfur hexafluoride has six electron pairs leading to an octahedral shape; methane has four electron pairs giving a tetrahedral shape; ammonia has four electron domains but one is a lone pair, giving a trigonal pyramidal shape rather than trigonal bipyramidal.