Why do we draw unbonded electrons in pairs?

  • Thread starter Leoragon
  • Start date
  • #1
43
0

Main Question or Discussion Point

A little background: I'm only a highschool student with some knowledge on Lewis dot structures. And I don't know much about the s orbitals or p orbitals or whatnot.

Why are there lone pairs? Shouldn't the electrons repel each other? Why do we draw them as pairs?

For example: carbon dioxide is drawn like this
CO222.png

Why don't we draw it like
CO22.png

or
CO2.png


or sulfur dioxide
SO2.png

Why not this?
SO22.png


Are the drawings just arbitrary and the original used for simplicity's sake?
Can all these drawings work?
 
Last edited:

Answers and Replies

  • #2
Simon Bridge
Science Advisor
Homework Helper
17,856
1,654
Electrons couple spin-spin inside their orbitals - thus: they tend to pair up. Inside a molecule, electrons are not static charges so all the diagrams are incorrect. However, if you work out the relative frces in the different configurations you drew, you'll find your drawings have the higher potential energy.

It's only a notation - not an accurate representation of the distribution of electrons in the molecule.
 
  • #3
43
0
Electrons couple spin-spin inside their orbitals - thus: they tend to pair up. Inside a molecule, electrons are not static charges so all the diagrams are incorrect. However, if you work out the relative frces in the different configurations you drew, you'll find your drawings have the higher potential energy.

It's only a notation - not an accurate representation of the distribution of electrons in the molecule.
I don't quite understand. I read http://chemwiki.ucdavis.edu/Physica...Quantum_Number_.26_(s.2C_p.2C_d.2C_f)_Orbital and to my understanding a pair of opposite spin electrons can occupy an orientation of an orbital? Is that why we say they are pairs?
So all those drawings are correct? I can draw that way if I wanted to?
Also, what notation would be an accurate representation?
 
  • #4
A little background: I'm only a highschool student with some knowledge on Lewis dot structures. And I don't know much about the s orbitals or p orbitals or whatnot.

Why are there lone pairs? Shouldn't the electrons repel each other? Why do we draw them as pairs?

For example: carbon dioxide is drawn like this
View attachment 82251
Why don't we draw it like
View attachment 82252
or
View attachment 82253

or sulfur dioxide
View attachment 82255
Why not this?
View attachment 82256

Are the drawings just arbitrary and the original used for simplicity's sake?
Can all these drawings work?
you can not do that,it is wrong.
 
  • #5
DrDu
Science Advisor
6,032
759
At least for elements from the first period (Na - Ne), there are only four valence orbitals available 1 s and 3 p type orbitals. Taking oxygen in CO2 as an example, you can form two bonding orbitals with C and two anti-bonding orbitals, which are too high to be occupied. The bonding orbitals are filled with two electrons from C and two electrons from O. This leaves 4 electrons on O which have to be distributed among 2 remaining orbitals. As each orbital may contain at most 2 electrons with anti-parallel spin ("pairs"), the only possibility is to have two pairs at O while the structures you did draw aren't possible.
 
  • #6
Simon Bridge
Science Advisor
Homework Helper
17,856
1,654
I don't quite understand. I read [chemwiki] and to my understanding a pair of opposite spin electrons can occupy an orientation of an orbital? Is that why we say they are pairs?
Yes. One spin up and one spin down.
This should hep you make sense of the convention in pairing up the dots. An unpaired dot would indicate would indicate an electron all by itself in the "orbital" - two unpaired dots would indicate that there are two different orbitals with only one electron in them.

So all those drawings are correct? I can draw that way if I wanted to?
Which way? You can draw them the way you did if you want to, and you don't care about other people being able to understand you, but the configuration is not as useful and it is not correct according to established conventions. Best to stick to the conventions.

Also, what notation would be an accurate representation?
There is no 100% accurate notation, it's a notation. It's just a way of keeping notes about what is important to you. When other things are important, you use a different notation. It's standardized because other people want to be able to read your notes.

As you advance in your studies you will probably get to learn more about the quantum mechanics behind these conventions and notations, and it will make more sense.
 

Related Threads on Why do we draw unbonded electrons in pairs?

Replies
2
Views
29K
Replies
2
Views
5K
Replies
2
Views
3K
Replies
12
Views
7K
Replies
2
Views
2K
Replies
0
Views
3K
Replies
2
Views
7K
Replies
3
Views
2K
Replies
1
Views
5K
  • Last Post
Replies
1
Views
10K
Top