[airplanet56]

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: NO^2-, 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.

[magician4]

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