Drawing Lewis Dot Diagrams: Rules Beyond the Octet Rule

In summary: The rest is just applying them correctly based on the given formula. In summary, when drawing Lewis dot diagrams, it is important to remember that carbon usually has a full octet, some atoms can become electron deficient or electron sufficient, and the Duet Rule applies for hydrogen. Additionally, when writing the formula, be sure to link OH if it is present. The general rules for drawing Lewis dot diagrams include knowing the number of valence electrons for different elements and ensuring that all atoms have a valence octet (except for hydrogen).
  • #1
bomba923
763
0
What are the rules for drawing Lewis dot diagrams, besides the

1) Carbon usually has a full octet
2) Some atoms become electron deficient, others electron sufficient
3) The Duet Rule
4) Link OH if written in the formula

What the "other" rules?

For example, i try to draw glucose, C6H12O6:
*I make a hexagon of six single-bonded carbon
*I attached a double-bond with oxygen to each carbon (carbon has 2 single bonds, and one double bond, so it obeys octet rule)
*I finally attach two single-bonded hydrogen to each oxygen.

Why doesn't this work? I have six carbon with octets, six double-bonded oxygen=carbon bonds (six oxygen), and two hydrogen at each oxygen

C-C-C-C-C-C with C=O, where each oxygen then bonds with two hydrogen

Why is this incorrect----what are the other rules for drawing lewis diagrams??
 
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  • #2
In this case, your oxygen atoms do not have octets. That is the main problem. Typically, for oxygen to have a neutral octet, it can support only 2 bonds (either one double-bond or two single bonds), but you are trying to give it 4 each.

In any case, expecting you to guess the structure of glucose by trial and error is quite unreasonable. It could take forever, and there's no good reason to make you try the gazillion possibilities before finding the correct one.
 
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  • #3
But the oxygens do have an octet--a double bond with the carbon, and two single bonds with hydrogen (one double bond+2 single bonds gives 8 electrons, doesn't it?)

Oxygen can have only "two" bonds for a neutral octet?

If so, these are the kind of rules I should know about; are there more such rules?
 
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  • #4
Gokul43201 said:
In this case, your oxygen atoms do not have octets. That is the main problem. Typically, for oxygen to have a neutral octet, it can support only 2 bonds (either one double-bond or two single bonds), but you are trying to give it 4 each.

Just for the record,Gokul,in any ORGANICAL COMPOUND THE OXYGEN HAS AN OCTET...Your assertion was made on an erroneous basis provided by the OP...

Daniel.
 
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  • #5
So then, the oxygens aren't the problem? Then what is?
 
  • #6
bomba923 said:
But the oxygens do have an octet--a double bond with the carbon, and two single bonds with hydrogen (one double bond+2 single bonds gives 8 electrons, doesn't it?)

Oxygen can have only "two" bonds for a neutral octet?

They do indeed.They have either double bond with the C or 2 simple bonds,1 with the C and one with the H.In this case...

Daniel.

P.S.Glucosis does not have a cyclic structure... :wink:
 
  • #7
dexter said:
Just for the record,Gokul,in any ORGANICAL COMPOUND THE OXYGEN HAS AN OCTET...
I know this Dexter. I was explaining to Bomba why his structure was infeasible.

bomba923 said:
So then, the oxygens aren't the problem? Then what is?
No, the oxygens are the problem. The only way to ensure an octet as well as the correct charge for oxygen is through 2 bonds and two unbonded pairs. With 4 bonds, you make an octet, but you only have 4 electrons contributed by O, whereas you need 6.
 
  • #8
Well then :smile: ...are there any other such rules I should know about?

Just curious, what are the other general rules?
 
  • #9
1. Know the number of valence electrons in different elements (O=6, C=4, N=5, H=1, Cl=7, etc.)
2. After sharing electrons all atoms must have a valence octet (except H, which gets a duet)

Really, these two are the only rules you need to know for most organic compounds.
 

1. What is the octet rule?

The octet rule states that, in most cases, atoms tend to form chemical bonds in order to achieve a stable electron configuration of 8 valence electrons.

2. Are there any exceptions to the octet rule?

Yes, there are exceptions to the octet rule. Atoms such as hydrogen, helium, and lithium can have stable configurations with less than 8 valence electrons, while atoms such as phosphorus and sulfur can have stable configurations with more than 8 valence electrons.

3. What are the general steps for drawing Lewis dot diagrams?

The general steps for drawing Lewis dot diagrams are:
1. Determine the total number of valence electrons for all atoms in the molecule.
2. Determine the central atom in the molecule.
3. Draw a skeletal structure, connecting all atoms with single bonds.
4. Place remaining electrons on the outer atoms, following the octet rule.
5. Place any remaining electrons on the central atom, following the octet rule.
6. Check the formal charges of all atoms to ensure they are as close to zero as possible.

4. What are the rules for drawing Lewis dot diagrams beyond the octet rule?

There are three main rules for drawing Lewis dot diagrams beyond the octet rule:
1. Expanded octets: Atoms in periods 3-7 can have expanded octets, meaning they can have more than 8 valence electrons in their outer shell.
2. Incomplete octets: Atoms in period 2 can have incomplete octets, meaning they can have less than 8 valence electrons in their outer shell.
3. Odd-electron molecules: Some molecules have an odd number of valence electrons, resulting in an unpaired electron. These molecules are known as free radicals.

5. How do I know if a Lewis dot diagram is correct?

To check the correctness of a Lewis dot diagram, you can follow these steps:
1. Count the total number of valence electrons in the diagram. It should match the total number of valence electrons for all atoms in the molecule.
2. Check the formal charges of all atoms. The sum of all formal charges should be equal to the overall charge of the molecule, if any.
3. Make sure all atoms have a complete octet, except for those with expanded or incomplete octets.
4. Check for any lone pairs of electrons on atoms, which should be placed in the outermost shell.
If all of these criteria are met, then the Lewis dot diagram is correct.

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