Chemical Forums

Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: oilypiggy on March 07, 2019, 11:07:29 PM

Title: VSEPR Theorum
Post by: oilypiggy on March 07, 2019, 11:07:29 PM

Hi Guys, can anyone help with this question?
Using the VSEPR model, the electron-domain geometry of the central atom in NO2- is _______
a) Linear
b)Trigonal Planar
c) Tetrahedral
d)Trigonal Bipyramidal
e)Octahedral

Thanks!

Title: Re: VSEPR Theorum
Post by: sjb on March 08, 2019, 02:00:12 AM

What are your thoughts? How many electron pairs are there around the central atom?

Title: Re: VSEPR Theorum
Post by: ChargePositive on March 08, 2019, 03:25:34 PM

Are you able to draw out Lewis structure for the molecule? If you are, classifying the shape is easy, and goes by the number of lone pairs of electrons and bonded pairs of electrons. You can always look up a VSEPR Chart that tells you what shape the molecule will be based on the electron pairs.

Title: Re: VSEPR Theorum
Post by: oilypiggy on March 08, 2019, 08:20:17 PM

I'm unsure of its 3 or 4 as i dont knwo if the double bond counts

Title: Re: VSEPR Theorum
Post by: AWK on March 09, 2019, 03:10:16 AM

both wrong
You must draw the Lewis structure correctly. Double or triple bonds in the Lewis structure count as "one pair" of electrons for the purpose of establishing the electron pair geometry.

Title: Re: VSEPR Theorum
Post by: oilypiggy on March 10, 2019, 09:35:29 PM

Doesn't the lone electron pair count as a domain too

Title: Re: VSEPR Theorum
Post by: AWK on March 11, 2019, 03:28:19 AM

The VSEPR method consists of several rules. I indicated only one that you omitted, indicating an incorrect answer This rule only indicates how to treat multiple bonds, and does not say anything about non-bonding electron pairs or individual non-bonding electrons. Without taking all rules into account, step by step, you will not get a correct answer.

Title: Re: VSEPR Theorum
Post by: oilypiggy on March 11, 2019, 07:12:49 AM

I am still incredibly lost, I count 3 electron domains still

Title: Re: VSEPR Theorum
Post by: AWK on March 11, 2019, 09:56:13 AM

So far correct. This excludes c, d, and e.

Title: Re: VSEPR Theorum
Post by: oilypiggy on March 11, 2019, 06:03:17 PM

Isn't linear 2 electron domains as well

Title: Re: VSEPR Theorum
Post by: AWK on March 11, 2019, 07:19:56 PM

So the problem is solved.

Title: Re: VSEPR Theorum
Post by: oilypiggy on March 14, 2019, 09:50:33 PM

I'm confused, what are you saying the answer is?

Title: Re: VSEPR Theorum
Post by: AWK on March 15, 2019, 04:27:22 AM

 

Quote

I count 3 electron domains still

Title: Re: VSEPR Theorum
Post by: oilypiggy on March 15, 2019, 10:19:12 PM

Isn't trigonal planar for a molecule with no lone pairs though

Title: Re: VSEPR Theorum
Post by: mjc123 on March 18, 2019, 09:13:41 AM

Are you confusing molecular geometry with electron-domain geometry?

Title: Re: VSEPR Theorum
Post by: oilypiggy on March 18, 2019, 07:32:07 PM

Possibly, I thought the electron domain of the particular molecule was bent but that isn't one of the answers given

Title: Re: VSEPR Theorum
Post by: AWK on March 19, 2019, 03:09:47 AM

This is a test with only one answer correct.

Title: Re: VSEPR Theorum
Post by: mjc123 on March 19, 2019, 05:43:07 AM

Quote

Possibly, I thought the electron domain of the particular molecule was bent but that isn't one of the answers given

You are confusing them. The electron domain geometry is trigonal planar, with a lone pair occupying one of the trigonal positions, and N-O bonds the other two. The molecular structure (arrangement of the atoms) is bent. Similarly, H₂O has a bent molecular structure, but a tetrahedral electron domain geometry at the oxygen (two bonds and two lone pairs).
You can't have a bent electron domain geometry. (What occupies the reflex angle?)

Title: Re: VSEPR Theorum
Post by: oilypiggy on March 19, 2019, 11:53:08 PM

Ah ok, i see i did get them confused, thank you for your help