## bond angles less than <109.5

(Polar molecules, Non-polar molecules, etc.)

Cavalli_1H
Posts: 92
Joined: Thu Sep 19, 2019 12:15 am

### bond angles less than <109.5

I realize that there are certain times when molecules form trigonal pyramidal shape the bond angle is <109.5, but can someone explain why? What makes this way and how do we know that it will be <109.5?

Sahil Jog 1F
Posts: 126
Joined: Thu Jul 11, 2019 12:16 am

### Re: bond angles less than <109.5

Even if a molecule with a trigonal pyramidal shape looks to be arranged tetrahedrally (bond angles=109.5), the lone electron pair has a greater electron repulsion strength than a bonded one, forcing the 3 bonded atoms closer to each other, and thus making their bond angles slightly less than 109.5.

AmyL_3L
Posts: 50
Joined: Fri Aug 09, 2019 12:17 am

### Re: bond angles less than <109.5

The lone pair on the central atom has greater repulsion strength. Therefore, it pushes the three bonded atoms closer to each other, decreasing their bond angles to be less than 109.5.

Sofia Barker 2C
Posts: 101
Joined: Wed Sep 18, 2019 12:21 am

### Re: bond angles less than <109.5

The bond angles of atoms within a molecule with a trigonal pyramidal shape are less than 109.5 degrees because the lone pair of electrons has greater electron repulsion, so the three bonding pairs are pushed closer together. Lone pairs have greater repulsion because they have a stronger negative charge and are closer to the central atom because, unlike bonding pairs, they are not being pulled away to be shared by another atom.

Erik Buetow 1F
Posts: 96
Joined: Fri Aug 30, 2019 12:15 am

### Re: bond angles less than <109.5

If there is a lone pair, it pushes the other atoms closer together, making the bond angles slightly less than 109.5