Question

if the molecular geometry with trigonal bipyramidal electron geometry (5 bonding sites) is seesaw, how many electron pairs does it have?
check it
a 3
b 1
c 2
d 0

Explanation:

Step1: Recall VSEPR theory

VSEPR theory states that the electron - pair geometry (trigonal bipyramidal in this case) and molecular geometry (seesaw) are related. For a trigonal bipyramidal electron - pair geometry, the formula for the number of bonding sites (\(b\)) and lone pairs (\(l\)) is based on the total number of electron groups (\(n=b + l\)). The trigonal bipyramidal electron - pair geometry has \(n = 5\) electron groups.

Step2: Relate molecular and electron - pair geometry

The seesaw molecular geometry occurs when there is \(1\) lone pair (\(l\)) and \(4\) bonding sites (\(b\)). But wait, no, let's re - check. The general formula for electron - pair geometry \(EPG\) (trigonal bipyramidal, \(EPG\) has \(5\) electron groups). The molecular geometry \(MG\) (seesaw) is of the form \(AX_4E\) (where \(A\) is the central atom, \(X\) is the surrounding atom, and \(E\) is the lone pair). The number of electron groups \(n=4 + 1=5\) (trigonal bipyramidal \(EPG\)).

Answer:

c 2