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bond angles less than <109.5

Posted: Sun Nov 17, 2019 8:28 am
by Cavalli_1H
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?

Re: bond angles less than <109.5

Posted: Sun Nov 17, 2019 10:01 am
by Sahil Jog 1F
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.

Re: bond angles less than <109.5

Posted: Sun Nov 17, 2019 11:15 am
by AmyL_3L
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.

Re: bond angles less than <109.5

Posted: Sun Nov 17, 2019 12:17 pm
by Sofia Barker 2C
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.

Re: bond angles less than <109.5

Posted: Sun Nov 17, 2019 12:27 pm
by Erik Buetow 1F
If there is a lone pair, it pushes the other atoms closer together, making the bond angles slightly less than 109.5