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### bond angle

Posted: Thu Nov 16, 2017 8:36 pm
I'm kind of confused about bond angles. Where exactly are the angles measured in relation to? Are they always measure in relation to the central atom?

### Re: bond angle

Posted: Thu Nov 16, 2017 8:51 pm
The bond angle is the angle between XAX (X being the surrounding atoms, and A being the central atom). Here is a useful chart that shows you what the angles are for any molecular shape. http://mmstcchemistry.weebly.com/upload ... ometry.pdf

### Re: bond angle

Posted: Thu Nov 16, 2017 9:04 pm
The bond angle for something is the angle between your central atom and the two directly attached to it.

For example, in water the bond angle is the angle created by H-O-H.

For a trigonal bipyramidal molecule like PF5, the bond angles are either 120 or 90 degrees. See the attached graphic... It's easier to see if you can visualize it in 3D space.  ### Re: bond angle

Posted: Thu Nov 16, 2017 10:10 pm
Why do we say bonds are less than 109 degrees or less than 120 degrees? I don't understand why it is "less than"

### Re: bond angle

Posted: Thu Nov 16, 2017 10:40 pm
Belle Calforda3f wrote:Why do we say bonds are less than 109 degrees or less than 120 degrees? I don't understand why it is "less than"

Lone pairs exert more repelling force against bonded pairs than do bonded against bonded. So if we know that a molecule is usually 120 degrees with all three electron densities bonded, and take away one of the bonded pairs and replace it with a lone pair, that lone pair will exert more force on the remaining two bonded pairs. With more force, the bond angle between the remaining two bonded pairs is slightly decreased, aka less than 120 degrees.