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Homework Problem 4.1

Posted: Wed Jul 24, 2019 12:43 am
by somyapanchal1D
4.1: Below are ball-and-stick models of two molecules. In each case, indicate whether there must be, may be, or cannot be one or more lone pairs of electrons on the central atom.

For this problem, I was confused about part b which shows a model of a linear molecule with a 180 degree bond angle. The solutions manual shows that there may be lone pairs of electrons on the central atom. I thought that a linear molecule (which always has a bond angle of 180) can never have lone pairs of electrons. Why in this case, can this molecule have lone pair(s) and still have a 180 degree angle.

Re: Homework Problem 4.1

Posted: Wed Jul 24, 2019 8:32 am
by Chem_Mod
A possibility of why there can be a linear shape with lone pairs is if you consider a molecule with 5 regions of electron density around the central atom, such as trigonal bipyramidal, see saw, and T. You can go even further and have all 3 of the equatorial regions be lone pairs, thus resulting in the 180 degree angle between the two axial atoms.

Re: Homework Problem 4.1

Posted: Wed Jul 24, 2019 11:15 am
by somyapanchal1D
What about the example of (CH2)2-. This molecule has a lewis structure of two single bonds of the hydrogen atom coming off of the central carbon atom along with two lone pairs of electrons on the carbon. What shape and bond angles would this result in?

Can a linear molecule have only 3 lone pairs in order to remain linear with 180 degree bond angles? Not 2 lone pairs?