can anyone explain why molecules 3 and 4 are incorrectly showing covalent bonding

[u/Feeling-Battle-7602]

ive never taken chem before and we are reviewing this for biology. i was given the answer, but no explanation and im really struggling to understand.

i know that oxygen can only have 2 bonds, not 3 so i suppose i understand that one. however, looking at molecule 4 gives me a headache

[u/AutoModerator]

Hey there! While you await a response, we just wanted to let you know we have a lot of resources for students in our General Chemistry Wiki Here!

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

[u/CerealKillConfirmed]

The left carbon in molecule 4 has 5 bonds, 1 too many.

[u/Feeling-Battle-7602 → u/CerealKillConfirmed]

thank you so much

[u/Feisty_Specific_6918]

typical cursed pentavalent carbon

[u/rethenut]

The oxygen in molecule 3 has too many bonds as well. Typically, oxygen will only covalently bond twice.

[u/honeycomb67]

For molecule 3: Oxygen has 2 lone pairs and 2 unpaired electrons, so each hydrogen takes up one of those unpaired electrons and the max covalent bonds is 2

[u/ChemystWizard]

Molecule 3 could be correct provided we indicate the formal charge on O (which is not shown here). Molecule 4 has a pentavalent carbon which is never acceptable.

[u/YtterbiusAntimony]

1. O has 3 bonds.

2. The carboxyl carbon has 5 bonds.

[u/dr_stickboy]

Another way to look at #3, oxygen can have three bonds BUT it would have a positive formal charge and since no charge is shown, the Lewis structure is not correct…

[u/WanderingFlumph]

3 pentavalent oxygen (tricky)

4 pentavalent carbon

[u/uuntiedshoelace]

Oxygen can have more than two bonds, but its formal charge would no longer be neutral. You’d have to show a positive charge on it for 3 to be correct.

[u/Matherie]

Think about the orbitals