Which Structure Below Is Not Correctly Drawn

Can You Spot the Wrong Lewis Structure? Here's What to Look For

You stare at a page with four or five Lewis structures, and the question is simple on the surface: which one is wrong? But then you actually try to figure it out, and suddenly nothing feels obvious. Consider this: is the charge in the right place? Did they forget a lone pair? Why does that bond look like it has too many electrons?

Here's the thing — most "which structure is not correctly drawn" questions aren't really about memorization. They're about whether you understand the rules* well enough to spot a quiet mistake. And the mistakes are usually small. That's what makes them tricky.

What This Type of Question Is Really Asking

When a chemistry problem asks you to identify the incorrect Lewis structure, it's testing a handful of specific things at once:

• Whether the total number of valence electrons is correct
• Whether each atom (especially the central atom) has a reasonable number of bonds
• Whether formal charges are minimized or at least consistent
• Whether the octet rule is satisfied where it should be (and broken only when it has to be, like for boron or in expanded octets)
• Whether lone pairs are drawn where they need to be

A structure can pass three of those checks and still be wrong because of the fourth. That's the part that trips people up.

Why It Matters Beyond the Test

Even if you're not studying for an exam, being able to read a Lewis structure carefully is one of those foundational chemistry skills. A wrong Lewis structure can lead you to predict the wrong molecular geometry, the wrong polarity, or the wrong reactivity. Get the structure wrong, and everything downstream is wrong too.

In organic chemistry, this gets even more important. Reaction mechanisms depend on which lone pairs are available and which bonds are polarized. A misplaced charge or a missing lone pair isn't just a cosmetic error — it changes the chemistry.

The Common Mistakes That Make a Structure "Wrong"

Let's walk through the actual problems you're most likely to see. These are the errors that show up over and over in textbook questions.

Off on the Total Electron Count

This is the most common error, and it's the easiest one to miss because the structure itself can look* reasonable. Every Lewis structure has to account for every single valence electron — no more, no fewer. If you're counting from the periodic table and the structure shows a different number of dots and dashes, something's off.

A quick way to check: count the electrons around each atom (a single bond = 2, a double bond = 4, a triple bond = 6, lone pair = 2) and add them up. On the flip side, compare that to what the molecule should have. If the numbers don't match, the structure is wrong even if everything else looks fine.

Octet Rule Violations That Don't Belong

Carbon, nitrogen, oxygen, and fluorine should always* have an octet in a standard Lewis structure. If one of them has only six electrons around it and there's no good reason for it, that's a problem. Phosphorus and sulfur can sometimes exceed the octet, and boron often has only six — but those exceptions are predictable, and the question usually targets a clear-cut violation.

A structure showing carbon with five bonds or nitrogen with only four electrons is wrong. Period.

Formal Charges That Don't Add Up

Here's a subtle one. And the sum of the formal charges in a Lewis structure must equal the overall charge of the molecule or ion. If you're looking at a neutral molecule and one of the answer choices has a +1 and a -1 that don't cancel to zero, that structure is wrong.

Even when the formal charges do sum correctly, the structure might still be the "bad" choice. In practice, a structure with unnecessary charges — when a better, lower-charge version is possible — is technically correct but is usually not the "best" answer. Practically speaking, best practice is to minimize formal charges overall and keep negative formal charges on the more electronegative atom. Test questions sometimes exploit that gray area, though, so be careful.

Wrong Central Atom

Sometimes the structure draws the wrong atom in the center. If a structure shows nitrogen on the outside and carbon in the middle with hydrogen bonded to nitrogen through carbon, that's wrong. A classic example: HCN. Hydrogen can never be the central atom because it can only form one bond. The carbon goes in the middle.

This one feels obvious once you see it, but in a list of similar-looking structures, it's easy to miss.

Bonding Patterns That Violate Known Behavior

You should also know the typical bonding behavior of common atoms:

• Hydrogen: 1 bond, no lone pairs
• Carbon: 4 bonds, no lone pairs
• Nitrogen: 3 bonds, 1 lone pair
• Oxygen: 2 bonds, 2 lone pairs
• Fluorine: 1 bond, 3 lone pairs
• Halogens in general: 1 bond, 3 lone pairs

If a structure shows oxygen with three bonds and one lone pair, that oxygen has a +1 formal charge. That can be correct in some ions, but if the molecule is neutral and a better structure exists, it's the wrong choice.

How to Actually Work Through the Problem

When you get a "which is not correctly drawn" question, don't just glance at the four options and pick the one that looks weird. Go through each one systematically.

Step 1: Count the Electrons

Tally the total valence electrons and compare to what the molecule should have. This alone eliminates a lot of wrong answers.

Continue exploring with our guides on how many pounds in 83 kilos and classify the following triangle check all that apply 54 36.

Step 2: Check the Octets

Walk through each atom. Are the octet-rule elements obeying the rule? Are the exceptions (boron, expanded octet elements) behaving as expected?

Step 3: Calculate Formal Charges

For each atom, formal charge = (valence electrons) – (non-bonding electrons) – (½ × bonding electrons). If anything looks weird — like a +2 on carbon or a –2 on hydrogen — you've found your problem.

Step 4: Look for the Central Atom Issue

Is hydrogen in the middle? Did they put the less electronegative atom on the outside where it belongs? This is fast to check and often the answer.

Step 5: Ask "Is This the Best Structure?"

Sometimes all four structures are technically valid, but one is clearly worse because of high formal charges or charges in the wrong place. The question usually wants you to pick the incorrect* one, though, so be sure of what it's actually asking.

What Most People Get Wrong About These Questions

The biggest mistake isn't a chemistry mistake — it's a strategy mistake. People try to evaluate the whole structure at once with their gut. That works for the really obvious errors, but it fails on the subtle ones. The subtle ones are where the points are.

Another common trap: students see a structure with brackets and a charge and assume it's wrong because they don't see that pattern often. But polyatomic ions like sulfate or phosphate legitimately need those brackets. Don't dismiss a structure just because it looks unfamiliar.

And here's one more thing most people miss: the "incorrect" structure might be wrong for a single* tiny reason — a missing lone pair on one atom, or one too many electrons somewhere. So the rest of the structure can be perfectly drawn. Don't let a mostly-correct structure fool you into thinking it's right.

Practical Tips That Actually Help

• Always count electrons first. It's the single most reliable check. If the count is off, you can stop.
• Memorize the typical bonding pattern for common atoms. Once you know that oxygen usually has 2 bonds and 2 lone pairs, deviations jump out at you.
• Practice formal charge calculation until it's automatic. Most "trick" questions hide behind formal charge math.
• Don't trust your eyes alone. A structure can look symmetric and clean and still be wrong. Use the rules.
• When in doubt, draw it yourself. If you're allowed to work it out on scratch paper, build the correct structure from scratch and compare. That's almost always faster than trying to find the flaw in someone else's drawing.

FAQ

What if two structures look wrong?

Go back to the rules. Usually only one violates a hard rule (octet, electron count, charge sum), while the other has a soft issue (like non-minimized formal charges). The hard-rule violation is the one the question is targeting.

Do I need to know expanded octets to answer these?

For introductory-level questions, usually not. But if the molecule involves sulfur, phosphorus, or anything in period 3 or below, you should at least consider it. Expanded octets are allowed for those atoms, not required.

**What if a structure

What if a structure is missing hydrogens?

If a structure is missing hydrogens, it's almost certainly incorrect. Hydrogen only forms one bond, so if you count the bonds and find an atom that "should" have a hydrogen but doesn't, that's your error. This is especially common in skeletal or condensed structures where the hydrogens are implied.

Can a structure be incorrect for having too many bonds?

Yes. In practice, carbon with five bonds, nitrogen with four, or oxygen with three — these are all red flags. Worth adding: the only common exception is carbon monoxide, where the unusual bonding pattern is part of what makes the molecule stable. Outside of CO, count your bonds carefully.

How do I handle structures with multiple central atoms?

Tackle them one atom at a time. So check the octet and formal charge for each central atom separately. A common trick is to have one atom drawn correctly and another drawn wrong, so don't just verify the first one and assume the rest are fine.

Wrapping Up

Lewis structure questions aren't really about memorizing rules — they're about training your eye to catch inconsistencies. The rules are simple on their own: count electrons, satisfy octets, minimize formal charges, and place charges sensibly. The challenge is applying them quickly and reliably when you're staring at four nearly identical drawings under time pressure.

The students who do well on these questions treat them like a checklist rather than a judgment call. They don't ask "does this look right?" — they ask "does this pass rule one, rule two, rule three?" That shift in approach is what separates guessing from solving.

If you take one thing from this article, let it be this: never trust a structure that looks* fine. On top of that, the whole point of these questions is that appearances deceive. Verify everything, assume nothing, and when you find a flaw, make sure it's actually the flaw the question is asking about.

Practice a few dozen of these with a structured method and the pattern recognition will start to feel automatic. At that point, you're not really "studying" anymore — you're just reading structures the way they're meant to be read.