hw 4.21d

(Polar molecules, Non-polar molecules, etc.)

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Taizha 1C
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hw 4.21d

Postby Taizha 1C » Wed Jun 13, 2018 10:40 pm

Why is the answer for 4.21d a trigonal pyramidal with 107 degrees? The question asked for the lewis structure and angle of N2H4.
I was wondering why the bond angle wouldn't be the same as part a in the same question for C2H4 that has a bond angle of 120 degrees.
Also, why couldn't a double or triple bond be formed between the two nitrogens?

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Re: hw 4.21d

Postby Chem_Mod » Wed Jun 13, 2018 11:22 pm

N2H4 will have a different structure than C2H4 due to the difference in valence electrons of N and C. For the N2H4 it is more stable for N not to form double bonds between each other so that each N will have 3 single bonds (2 to Hs and 1 to the other N) and one lone pair giving it a formal charge of 5-(3+2)=0. So for each N they have four regions of electron binding, 3 bonds and a lone pair, so they are going to be trigonal pyramidal. Since this is a derivative of the tetrahedral geometry its angles will be similar to that of a tetrahedral, but slightly less due to the electron repulsion from the lone pair. In C2H4 the two carbons will prefer to have a double bond between them so that they can each have a double bond and two single bonds attached giving them a formal charge of 4-(0+4)=0. Since the C2H4 will have the double bond in the middle and two single bonds it will have three regions of electron binding make it trigonal planar. This will give it angles of 120 degrees.

Megan Phan 1K
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Joined: Fri Apr 06, 2018 11:04 am

Re: hw 4.21d

Postby Megan Phan 1K » Thu Jun 14, 2018 5:52 pm

It is more stable for N in N2H4 to not have double bond. So N will have 3 bonds w H and 1 lone pair. This is trigonal pyramidal which is equal to 107 degrees. C2H4 would be able to have a double bond hence the different answers.

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