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lone pair influence on shape

Posted: Sun Nov 18, 2018 10:24 pm
by Layla Manoochehri
can someone explain conceptually why the presence of a lone pair will change the shape, for example from linear to bent?

Re: lone pair influence on shape

Posted: Sun Nov 18, 2018 10:28 pm
by Ethan Yi 1K
the lone pair of electrons has a negative charge that will repel the bonding pairs that also have a negative charge, changing the shape.

Re: lone pair influence on shape

Posted: Sun Nov 18, 2018 10:32 pm
by 405021651
Lone pairs take up more space than a regular bond would take

Re: lone pair influence on shape

Posted: Sun Nov 18, 2018 10:33 pm
by jessicahe4Elavelle
Electrons are negatively charged and repulse other electrons. A lone pair causes an area of high electron density so electrons repel each other more strongly than bonding pairs causing a distortion in the shape (lower angle).

Re: lone pair influence on shape

Posted: Sun Nov 18, 2018 10:33 pm
by Angel Chen 2k
The presence of lone pair around the central atom affects the bond angle. A lone pair of electrons always tries to repel the bonded electrons, when electron pairs move away from each other, the shape of the molecule is affected.

Re: lone pair influence on shape

Posted: Sun Nov 18, 2018 10:34 pm
by Cody Do 2F
Hey, Layla!

For lone pairs, you have to see them as extremely repulsive in nature (they push everything, including bonds and other lone pairs, away from them). A linear molecule is flat and linear because the two atoms connected to the central atom want to be as far away from each other as possible. In order to achieve this maximum distance, the two atoms are directly opposite each other, forming a linear shape. However, if you introduce a lone pair into the equation, this all changes. This lone pair adds another region of electron density around the central atom (a linear molecule has two electron densities AKA the two bonds, this new one has three AKA the two bonds and the lone pair). Now that there are three regions of electron density, they'll all attempt to spread out around the molecule equally. If this were three bonds instead of two bonds + one lone pair, then the bond angle would be 120 degrees and the molecule would be trigonal planar. However, since we have the lone pair (and since lone pairs are extremely repulsive), the two bonds are pushed even further away from the lone pair. This is why water has a bent shape with a bond angle of 104.5 degrees—the lone pair's strong repulsion forces the two hydrogen atoms farther away from where the lone pairs are!

Re: lone pair influence on shape

Posted: Sun Nov 18, 2018 10:51 pm
by 905096106
Lone pairs disrupt the shape by making the angles between molecules smaller

Re: lone pair influence on shape

Posted: Sun Nov 18, 2018 11:06 pm
by Simran Rai 4E
Also in discussion, my TA had said that paired electrons are more repulsed by lone pairs of electrons than they are by other bonded pairs of electrons. Which can also explain why they'd more readily move closer to another bonded pair in the presence of lone electrons.

Re: lone pair influence on shape

Posted: Sun Nov 18, 2018 11:08 pm
by MichaelMoreno2G
Can someone explain the difference between bent and linear?

Re: lone pair influence on shape

Posted: Sun Nov 18, 2018 11:17 pm
by Simran Rai 4E
MMoreno3K wrote:Can someone explain the difference between bent and linear?


A linear shape is when the bond angles are 180 degrees exactly. This could even take place in the presence of 2 or more lone pairs depending on the amount of regions of electron density. A bent shape, however occurs when the linear shape is offset by a pair(s) of lone electrons that push the otherwise "linear" molecule's bond angles closer together due to electron repulsion.

Re: lone pair influence on shape

Posted: Sun Nov 18, 2018 11:40 pm
by Andrew Lam 3B
Lone pairs take up more space than bonding pairs, depressing the bond angle.

Re: lone pair influence on shape

Posted: Mon Nov 19, 2018 8:13 am
by Sapna Ramappa 1J
Because lone pairs have a high electron density, they take up more space. As a result, lone pairs are able to push the angles of the other bonds away from the lone pairs, thus changing the shape.

Re: lone pair influence on shape

Posted: Mon Nov 19, 2018 10:00 am
by Connie Chen 3D
Lone pairs take up a lot of space and have a ton of repulsion around them so the bonded elements get pushed away.

As for bent vs linear, linear is as it sounds like. A straight line with bond angles of 180 degrees. This only occurs when there are no lone pairs to cause repulsion. When there are lone pairs, then the molecule will be bent because the lone pairs cause the bonded elements to move away from the electrons.