Q1BasicCarbon count
How many carbons are in this bond-line structure?
Show answer
5 carbons.
There are two endpoints and three internal corners. Each endpoint or corner represents one carbon unless another atom is written.
Structure and Bonding · Practice Workbook
Bond-Line Drawing Practice
Twenty focused questions on reading, counting, and interpreting bond-line structures. Use these before moving into formal charge and resonance.
Rule to remember
Every endpoint and corner is a carbon unless another atom is written. Hydrogens on carbon are usually hidden.
How to use this page
Try each question first. Then open the answer. If you miss a question, write down the exact rule you forgot: endpoint, corner, heteroatom, hidden hydrogen, or multiple bond. Tally up the number of mistakes, and keep practicing!
Part A
Basic recognition
Q2BasicBranching
How many carbons are in this branched structure?
Show answer
6 carbons.
The main zigzag has five carbons. The downward branch adds one more carbon at its endpoint.
Q3BasicHidden hydrogens
How many hydrogens are attached to the marked carbon?
Show answer
2 hydrogens.
The marked carbon has two single bonds to other carbons. Carbon wants four bonds total, so two hydrogens are hidden.
Q4BasicHidden hydrogens
How many hydrogens are attached to the marked terminal carbon?
Show answer
3 hydrogens.
A terminal carbon with one single bond needs three hydrogens to reach four total bonds.
Q5BasicMultiple bonds
Identify the multiple bond shown in this structure.
Show answer
A carbon-carbon double bond.
Two parallel lines between the same two carbons represent a double bond. This makes the structure an alkene.
Q6BasicMultiple bonds
Identify the multiple bond shown in this structure.
Show answer
A carbon-carbon triple bond.
Three parallel lines between the same two carbons represent a triple bond. This makes the structure an alkyne.
Q7BasicHeteroatoms
How many carbons are in this alcohol? Do not count oxygen as carbon.
Show answer
4 carbons.
The zigzag has four carbon positions. The written OH is a heteroatom group, not an extra carbon.
Q8MediumHeteroatoms
How many carbons are in this ether?
Show answer
4 carbons.
There are two carbons on each side of the oxygen. Oxygen is written explicitly and is not counted as carbon.
Q9MediumCarbonyl
How many total carbons are in this carbonyl-containing molecule?
Show answer
4 carbons.
The carbonyl carbon is the atom at the base of the double-bonded oxygen. Then the chain continues through three more carbons.
Q10BasicRings
How many carbons are in this ring?
Show answer
6 carbons.
Every corner of the hexagon is a carbon. A six-membered carbon ring has six carbons.
Part B
Drawing interpretation
Q11MediumRings
How many hydrogens are on each alkene carbon in this ring double bond?
Show answer
1 hydrogen on each alkene carbon.
Each alkene carbon is bonded to one ring carbon by a single bond and to the other alkene carbon by a double bond. That gives three bonds drawn, so each has one hidden hydrogen.
Q12MediumReactant vs product
What changed from reactant to product?
Show answer
Br was replaced by OH; the carbon skeleton stayed the same.
The three-carbon chain is unchanged. Only the group attached to the terminal carbon changed from bromine to hydroxyl.
Q13BasicConversion
Convert the expanded formula shown into a bond-line drawing. How many endpoints/corners should the bond-line drawing have?
Show answer
Three carbons: two endpoints and one internal corner.
CH₃-CH₂-CH₃ is propane. In bond-line form, it has three carbon positions.
Q14MediumMistake spotting
What is wrong with this bond-line drawing style for a normal hydrocarbon?
Show answer
The carbons should not be written as CH2 in a normal bond-line hydrocarbon.
Carbon atoms are implied at endpoints and corners. You usually write heteroatoms, charges, and necessary hydrogens, not every carbon.
Part C
Conversion and mistake spotting
Q15BasicEndpoints
In a straight bond-line chain with 4 carbons, how many endpoints are present?
Show answer
2 endpoints.
A non-ring chain always has two ends. The remaining carbons are internal corners or bends.
Q16BasicCorners
In a zigzag bond-line drawing, what does an unlabeled corner represent?
Show answer
A carbon atom with enough hidden hydrogens to make four bonds.
This is the main shortcut of bond-line drawings. Corners are carbons unless another atom is written there.
Q17MediumHydrogen count
A carbon in a bond-line structure has one double bond and one single bond to other atoms. How many hydrogens does it usually have?
Show answer
1 hydrogen.
A double bond counts as two bonds and a single bond counts as one. That makes three bonds, so one hydrogen is added to reach four.
Q18HardHydrogen count
A carbon in a bond-line structure has one triple bond to another carbon. It is terminal. How many hydrogens does it have?
Show answer
1 hydrogen.
A terminal alkyne carbon has three bonds from the triple bond and one hidden hydrogen. Total bond count is four.
Q19MediumHeteroatoms
In bond-line drawings, are hydrogens attached to oxygen usually hidden like hydrogens on carbon?
Show answer
No. Hydrogens on heteroatoms are usually shown.
Carbon hydrogens are usually hidden. Hydrogens attached to O, N, S, and halogens are normally written because they affect charge, acidity, and reactivity.
Q20HardInterpretation
A molecule is drawn as a pentane chain with an alcohol at carbon 2. How many carbons and oxygens does it contain?
Show answer
5 carbons and 1 oxygen.
The five-carbon chain gives five carbons. The OH group contributes one oxygen and one hydrogen, not another carbon.
Next lesson
Learn Formal Charge
Now that you can read bond-line structures, the next step is learning how to assign formal charge. This section teaches the rule, the formula, and how to recognize charged atoms in organic molecules.
Start Formal Charge Lesson