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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: confusedstud on February 20, 2013, 07:31:33 AM

Title: Finding net dipole moments in 3D structures
Post by: confusedstud on February 20, 2013, 07:31:33 AM
How can I visualize the net dipole moment in 3D structures? For example, in CH4 , it is deemed non polar. However, I don't quite 'see' it. The pyramidal base has a dipole moment acting upwards and the top of it where there is a C-H bond, it acts downwards. So it cancels out and has no net dipole moment.

I am unable to understand how they cancel out. So for a lot of 3D structures like CH3 CH2 CH3 or CH3 CF2 CH3 I can't really tell by myself about their net dipole moments. I would have to google it.

Can someone enlighten me? Thanks  :)
Title: Re: Finding net dipole moments in 3D structures
Post by: sjb on February 20, 2013, 09:51:24 AM
Quote from: confusedstud on February 20, 2013, 07:31:33 AM
How can I visualize the net dipole moment in 3D structures? For example, in CH4 , it is deemed non polar. However, I don't quite 'see' it. The pyramidal base has a dipole moment acting upwards and the top of it where there is a C-H bond, it acts downwards. So it cancels out and has no net dipole moment.

I am unable to understand how they cancel out. So for a lot of 3D structures like CH3 CH2 CH3 or CH3 CF2 CH3 I can't really tell by myself about their net dipole moments. I would have to google it.

Can someone enlighten me? Thanks  :)

Are you comfortable with resolving forces or other applied maths like mechanics?
Title: Re: Finding net dipole moments in 3D structures
Post by: confusedstud on February 20, 2013, 10:49:22 AM
I have only resolved forces in 2 dimensions in my physics class. Or do we usually learn how to resolve forces or other vector quantities in 3 dimensions before learning about this?

Thanks :)
Title: Re: Finding net dipole moments in 3D structures
Post by: sjb on February 22, 2013, 02:43:08 AM
Usually is perhaps a difficult question to answer, as different places have different syllabuses. However, perhaps try it and see if that helps. It's just an extension of 2-d resolution, after all.
Title: Re: Finding net dipole moments in 3D structures
Post by: confusedstud on February 22, 2013, 07:08:15 AM
I can't really do it for long molecules like CH3CF2CH3 because that's when everything gets more confusing. How would students actually visualize them because I really can't.. It's like in CH4 i know it's non polar from the textbook I'm reading. However, I can't really explain it because if i look at the pyramidal structure CH3, its supposed to be equal to the C-H on the top which i can't visualize. But if i look at the sides of it like breaking it into 2 Vs then it makes more sense. But then again I can use that in the longer molecules so I'm pretty confused.