Determining VSEPR bond angles

[Jerome Mercado 2J]

How do you calculate the VSEPR bond angles between several atoms in a molecule?

An example:

For 4.7 (a) What is the shape of the thionyl chloride molecule, SOCl2? Sulfur is the central atom. (b) How many different OSCl bond angles are there in this molecule? (c) What values are expected for the OSCl and ClSCl bond angles?

The bond angle for OSCL is 107 degrees from VSEPR model with AB3X1 (3 atoms 1 lone pair on S). I am unsure to calculate the angle between two Cl atoms but I know it should be less than 107 degrees.

[Rylee Nelsen 3A]

For the SOCl2 the oxygen atom and two chlorine atoms are both singularly bonded to sulfur. Also, sulfur has a lone pair. So, because there are four regions of electron density with one lone pair, then the shape would be trigonal pyramidal. In part b, all of the OSCL angles would be the same because the lone pair would repel them equally. For part c, since the shape is a trigonal pyramidal, the angles would have to be less than 109.5 so somewhere in the 106 to 107 degree range. Hope this helps!

[Ava Kjos 1D]

Each different geometric shape has implied bond angles. For instance, trigonal planar will always be 120 degrees, linear will be 180 degrees, tetrahedral will 109.5 degrees and so on. You won't need to calculate any bond angles, you will just have to figure out the shape and then use the bond angles that go with that shape.

[Jerome Mercado 2J]

Thanks for the help.

In lecture, Dr. Lavelle did confirm that we do not need to calculate bond angles but we should know how lone pairs influence bonding angles between other atoms therefore a difference in angles between different atoms.

[Raphael_SanAndres3C]

Will we be tested on bond angles at all? If so, is there a set amount of angles that we should memorize?

[Sameen Mahmood 3D]

Will we be tested on bond angles at all? If so, is there a set amount of angles that we should memorize?

I definitely think we will be tested on them considering they're discussed in lectures, discussions, and homework. Plus it helps you to visualize the spatial arrangement of the molecule in terms of 360 degrees which lets you think about the location of atoms in each plane. I would memorize them all, and as long as you know that lone pairs repel more you can recognize when atoms have <120 deg or <109.5 deg and so on.