Page 1 of 1

### Bond Angles

Posted: Sat Nov 16, 2019 5:20 pm
How do you calculate the bond angles for molecules?

### Re: Bond Angles

Posted: Sat Nov 16, 2019 5:30 pm
The bond angles are just experimental observations, so some of the angles just have to be memorized. Lavelle said that we just have to know when to assume a bond angle will be less than another if it has more lone pairs, etc.

### Re: Bond Angles

Posted: Sat Nov 16, 2019 6:02 pm
^This is true. You can't really calculate the bond angles, they must be measured in a lab.

### Re: Bond Angles

Posted: Sat Nov 16, 2019 6:58 pm
You just need to memorize the bond angles for the basic molecular shapes without lone pairs, and understand that lone pairs make the angles slightly less than what they are.

### Re: Bond Angles

Posted: Sat Nov 16, 2019 8:50 pm
I think you find it out experimentally. The way you know for a test is just memorizing

### Re: Bond Angles

Posted: Sat Nov 16, 2019 8:54 pm
The book says it is impossible to predict the extent of distortion of bond angles when lone pairs are present. The only way to determine the value would be to measure it experimentally or calculate it with the Schrodinger eqn (which we don't have to do)

### Re: Bond Angles

Posted: Sat Nov 16, 2019 8:57 pm
Bond angle measurements have to be done experimentally but certain angles you can tell right away by seeing the lewis structure, such as those of a linear molecule or trigonal planar.

### Re: Bond Angles

Posted: Sat Nov 16, 2019 9:32 pm
Ramneet Sandhu 3D wrote:How do you calculate the bond angles for molecules?

Bond angle are something that you just have to memorize (109.5 for tetrahedral, etc.). However, many bond angles for molecules are quite intuitive, for example, for linear it is 180.

It can be confusing when an angle of less than an angles, but that is only when there is a lone pair. Foe example, for trigonal pyramidal, because of the repulsion of the lone pair, the angle is less than 109.5.

### Re: Bond Angles

Posted: Sun Nov 17, 2019 12:59 am
The ones that are set because of the symmetry of the molecule are:
linear - 180
trigonal planar - 120
tetrahedral - 109.5
square planar - 90

for the shapes that happen when there's a lone pair on the central atom, to calculate bond angle you are supposed to treat that lone pair as an atom, and then make it slightly less. For example, with an angular/bent shape with AX2E notation, the angle between the two atoms would be slightly less than 120. This is because the lone pair has more repulsion than a bonded pair; the electron cloud would be larger for the lone pair because only one atom is holding it in place, versus two atoms holding the bonded pair.