How many hydrogen atoms complete neutral methane with one carbon and four single bonds?
Answer and explanation
4
Four C–H bonds satisfy the ordinary valence-four carbon model.
Subjects
Organic chemistry
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Sample exercises
Which representation gives connectivity rather than just an atom count?
- A structural formula.
- Only a molecular formula.
- Only a sample mass.
Answer and explanation
A structural formula.
Connectivity indicates how atoms are joined.
In ethene CH₂=CH₂, what is the bond order of the bond between the carbons?
Answer and explanation
2
A double bond has bond order two in the simple model.
Which is conventionally treated as an inorganic carbon compound?
- Ethanol.
- Carbon dioxide.
- Ethane.
Answer and explanation
Carbon dioxide.
Carbon dioxide is a standard exception to the broad carbon-based description of organic chemistry.
Why can one molecular formula describe different organic compounds?
Answer and explanation
The same atom counts can be connected or arranged differently.
Distinguish composition from structure.
How many carbon atoms are written in CH₃CH₂CH₃?
Answer and explanation
3
There are three carbon-containing groups.
Study notes
Carbon frameworks and structural formulas
Read connectivity rather than only counting letters in a molecular formula.
Grades 8–11Carbon frameworks and structural formulas · Revision sheet
Read connectivity rather than only counting letters in a molecular formula.
Grades 8–11Straight-chain alkanes and names
Use carbon count and the limited scope of the alkane formula.
Grades 9–12Straight-chain alkanes and names · Revision sheet
Use carbon count and the limited scope of the alkane formula.
Grades 9–12Branched alkanes and locants
Choose a parent chain and explain what a position number means.
Grades 10–12Branched alkanes and locants · Revision sheet
Choose a parent chain and explain what a position number means.
Grades 10–12Alkenes, alkynes and unsaturation
Recognize bond types and the restrictions of simple formula patterns.
Grades 10–12Alkenes, alkynes and unsaturation · Revision sheet
Recognize bond types and the restrictions of simple formula patterns.
Grades 10–12Recognize common functional groups
Locate the actual group rather than classifying by one atom alone.
Grades 10–12Recognize common functional groups · Revision sheet
Locate the actual group rather than classifying by one atom alone.
Grades 10–12Alcohols and ethers: structure and properties
Compare connectivity and hydrogen-bond donor ability.
Grades 10–12Alcohols and ethers: structure and properties · Revision sheet
Compare connectivity and hydrogen-bond donor ability.
Grades 10–12Aldehydes and ketones
Read the groups attached to the carbonyl carbon.
Grades 10–12Aldehydes and ketones · Revision sheet
Read the groups attached to the carbonyl carbon.
Grades 10–12Carboxylic acids and esters
Identify structural differences without laboratory synthesis instructions.
Grades 10–12Carboxylic acids and esters · Revision sheet
Identify structural differences without laboratory synthesis instructions.
Grades 10–12Amines, amides and basicity
Locate nitrogen relative to a carbonyl before making comparisons.
Grades 10–12Amines, amides and basicity · Revision sheet
Locate nitrogen relative to a carbonyl before making comparisons.
Grades 10–12Constitutional isomers and stereoisomers
Tell changed connectivity from changed spatial arrangement.
Grades 10–12Constitutional isomers and stereoisomers · Revision sheet
Tell changed connectivity from changed spatial arrangement.
Grades 10–12Chirality and geometric isomerism
Recognize when spatial labels require enough structural information.
Grades 11–12Chirality and geometric isomerism · Revision sheet
Recognize when spatial labels require enough structural information.
Grades 11–12Monomers, repeat units and polymer properties
Connect long-chain structure with properties without universal recyclability claims.
Grades 9–12Monomers, repeat units and polymer properties · Revision sheet
Connect long-chain structure with properties without universal recyclability claims.
Grades 9–12Spectroscopy: combine clues carefully
Use simplified provided evidence instead of treating one peak as a full identification.
Grades 11–12Spectroscopy: combine clues carefully · Revision sheet
Use simplified provided evidence instead of treating one peak as a full identification.
Grades 11–12Acyclic alkane hydrogen count
This rule requires an acyclic saturated hydrocarbon.
Grades 9–12One-double-bond hydrocarbon
CnH2n applies here to an acyclic hydrocarbon with one double bond. A formula alone does not distinguish an alkene from a cycloalkane.
Grades 10–12Carbon balance on combustion
In complete hydrocarbon combustion, each carbon atom contributes one CO₂ molecule. This is a paper stoichiometry model.
Grades 10–12Alcohol-family molar mass
For a saturated acyclic monohydric alcohol, CnH2n+2O, sum all atom masses. The formula is also compatible with ether isomers.
Grades 10–12Hydrocarbon unsaturation index
For a neutral closed-shell hydrocarbon, each ring or double bond adds one DBE; a triple bond adds two.
Grades 11–12Polymer repeat-unit mass model
Multiply repeat-unit molar mass by the number of repeat units. This simplified model ignores end-group masses.
Grades 10–12Organic chemistry · Formula reference 1
Formula reference
Grades 9–12Organic chemistry · Formula reference 2
Formula reference
Grades 10–12Organic structure evidence and spectroscopic caution
A molecular formula constrains composition but can correspond to multiple constitutional or stereochemical structures.
UniversityOrganic structure evidence and spectroscopic caution · revision notes
A molecular formula constrains composition but can correspond to multiple constitutional or stereochemical structures.
University