Determining Bond Angle

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805132275
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Joined: Fri Sep 28, 2018 12:26 am

Determining Bond Angle

Postby 805132275 » Tue Nov 27, 2018 2:49 pm

When determining the bond angle of a moleucule, for example, SOCl2, do we consider the atom arrangement (tetrahedral with 109.5 degree bonds) or the actual shape's (trigonal pyramidal) bond angle? I know the answer is slightly less than 109.5 but im not completely sure why?

Anushi Patel 1J
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Re: Determining Bond Angle

Postby Anushi Patel 1J » Tue Nov 27, 2018 3:44 pm

You first should consider the electron arrangement (tetrahedral) to get an estimate of the angle being 109.5. However, you should take into consideration that since the shape is actually trigonal pyramidal and there are lone pairs, the angle will be slightly less than 109.5, since lone pairs have more electron repulsion.

Chloe Thorpe 1J
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Joined: Fri Sep 28, 2018 12:16 am

Re: Determining Bond Angle

Postby Chloe Thorpe 1J » Tue Nov 27, 2018 3:46 pm

From my understanding, we use the actual shape (trigonal pyramidal). The bond angle is slightly less than 109.5 because the atom arrangement (which I call the parent shape) is tetrahedral, which has bond angles of 109.5 like you stated. But, trigonal pyramidal shapes have a lone pair, which sort of pushes down on the atoms to make them slightly closer together than 109.5. The lone pair repels the other bonding pairs. Hope that helps

Heesu_Kim_1F
Posts: 60
Joined: Fri Sep 28, 2018 12:18 am

Re: Determining Bond Angle

Postby Heesu_Kim_1F » Tue Nov 27, 2018 3:47 pm

I would consider both atom arrangement and its actual shape. The reason the bond angle for SOCl2 is less than 109.5 is because its actual shape as a trigonal pyramidal has one lone pair of electrons, which affects the bond angles to be slightly less than 109.5 rather than 109.5 exactly. Also, Dr. Lavelle mentioned that we just have to know that it is <109.5 and not its exact bond angle if the molecule contains one or more lone pairs of electrons. But you would have needed to know that the 109.5 comes from its atom arrangement as tetrahedral in terms of areas of electron density. Hope this helps!


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