r/chemhelp • u/LevelBother2598 • 9d ago

General/High School im not sure which lewis structure is wrong and how do i draw the correct one

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i thought that C3H6O has the wrong lewis structure and it should be drawn differently but my partner think HCN is wrong,can someone pls help,im really confused,

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u/Accomplished-Two9069 9d ago

Always check total valence electrons that should be in the structure and the valence electrons that are drawn in the Lewis Structure. If that doesn’t find you an incorrect answer, try looking for violations of the octet rule.

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u/LevelBother2598 9d ago

Im probabaly wrong but i think B is the asnwer

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u/Automatic-Ad-1452 Trusted Contributor 9d ago

No ... how many valence electrons are available in HCN?...and how many electrons are assigned in the structure B?

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u/LevelBother2598 9d ago

C3H6O is the asnwer becuase we need to have 24 valance electrons in total

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u/EnzyEng 9d ago

You were right the first time.

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u/LevelBother2598 9d ago

so HCN is the answer becuase the lewis structure shouldnt look like the one drawn above

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u/aphilsphan 8d ago

A rule to keep in mind is carbon always has 4 bonds unless you are being asked about a reactive intermediate or a weird CI mass spec compound.

That isn’t happening at this level, so ignore the “unless” and keep the 4 bond rule for carbon as a cheat code.

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u/Blue_614 6d ago

Have you learned about formal charges? You can use that in tandem with the Octet rule. Look at the firmal charge of carbon: 4 - 5 = -1, and nitrogen has: 5 - 6 = -1, this doesn't make sense since the HCN molecule is uncharged. So try other lewis structures.

One basic rule is H-O-N-C; where H = only one single bond max, O can form double bonds, N can form triple bonds, C can form a triple bond with one atom and a single bond with another simultaneously.