Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: airplanet56 on June 29, 2013, 12:47:24 PM
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When you have a covalent compound with one of the elements: C, O, N, S, and P, I realize that a double bond can be formed. However, how do you know whether a double bond should be formed or lone pairs should be placed on the central atom. I frequently experience this problem with nitrogen and oxygen compounds such as: NO2-, NO2, and NO2+.
So, is their a rule to determine whether to make a double/triple bond or put the central atoms on the central atom? Like in CO2, there are two double bonds. There could be 1 double bond, 1 single bond, and 6 electrons dots on one oxygen and 4 on the other. The Carbon would have 2 dots, then.
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as a basic concept you'd introduce double- (or even triple- : see elementary nitrogen) bonds whenever (and only then) you need them to match the octet rule for all atoms in the substance
note that this concept only is a rule of thumb for beginners, and that some substances ( for example NO ) can't be made to match this concept no matter what you try (--> uneven number of electrons involved: "octet" is impossible)
:rarrow:those you will have to learn
also note, that in the beginning you might have to learn some substances with their Lewis-structures in a way that violates this rule (sulfuric acid for example: this will be presented as "hypervalent" with 10 electrons to you in the beginning: S(=O)2(OH)2 )
regards
Ingo