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### Double Bonds and Electron Numbers

Posted: Thu Oct 24, 2019 2:20 am
Don't know if this question is for Lewis Structures or Resonance but here we go anyways.
Can someone explain how double covalent bonds change the number of electrons of a compound? Like why does making one of the NO bonds a double covalent bond for the compound NO3- change the number of valence electrons in the whole compound from 26 electrons (if there were each element has an octet) to 24 electrons. How are the electrons counted in covalent bonds, double covalent bonds, triple covalent bonds?

### Re: Double Bonds and Electron Numbers

Posted: Thu Oct 24, 2019 2:51 am
When you draw lewis structures, make sure that you are aware of the number of electrons that are available from the elements and the octet rule. For NO3-, it was 24 electrons. For each element, you want to share until each of them has 8 electrons. So originally when there was only a single bond bounded for each oxygen to nitrogen, nitrogen only had 6 electrons as a result but there were already 24 electrons drawn (oxygen reaching 8 from the result of bonding and nitrogen having 6 from the result of bonding). However, we want to have 8 electrons for nitrogen as well so by drawing the double bond for one of them we can give nitrogen 8 electrons while drawing less free valence electrons for that double-bonded oxygen without changing the number of electrons drawn in the diagram.

In single covalent bonds, it's 2 electrons; double bonds, it's 4 electrons, and triple bonds have 6 electrons being shared between.

### Re: Double Bonds and Electron Numbers

Posted: Thu Oct 24, 2019 6:18 pm
when do you know to turn into a double bond instead of leaving the electrons on the other side of the element when drawing a lewis structure?

### Re: Double Bonds and Electron Numbers

Posted: Thu Oct 24, 2019 6:38 pm
Arianna Perea 3H wrote:when do you know to turn into a double bond instead of leaving the electrons on the other side of the element when drawing a lewis structure?

You would turn into a double bond when the total number of electrons you drew for the elements exceeds the total number of electrons of the compound you have counted. For example, in NO3-, the total number of electrons counted is 24, but when you drew the Lewis structure with only single bonds and electrons on the side, there is a total of 26 electrons, which means there are not enough electrons to fulfill this structure, so you would turn one pair of electrons on the side of the element into a double bond.

### Re: Double Bonds and Electron Numbers

Posted: Thu Oct 24, 2019 6:42 pm
Arianna Perea 3H wrote:when do you know to turn into a double bond instead of leaving the electrons on the other side of the element when drawing a lewis structure?

It would depend on the total number of electrons you have to work with (valence electrons of every atom, adjusting for net charge if there is any).

Otherwise, there are some circumstances where the bonds would be different because of formal charge, which Dr. Lavelle is probably going to go over soon.