CLASS 10 SCIENCE · CHAPTER 4 · STUDY NOTES
Carbon and its Compounds
An exploration of the versatile nature of carbon, its covalent bonding, the formation of diverse organic compounds, and the chemistry of soaps and detergents.
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Bonding in Carbon: The Covalent Bond
Count shared and unshared electron pairs without confusing a molecule with an ionic lattice.BUILD · CHANGE · EXPLAIN
Shared pairs hold the atoms together.
Predict: how many electrons does each atom count in a shared pair?
Each H counts both shared electrons: a filled first shell.
Shared pairs and lone pairs
Count each atom’s own lone electrons plus both electrons in every shared pair. Can each atom count eight?
Each colour traces the electrons contributed by one atom; electrons are not fixed coloured beads. Bond lines replace shared pairs, while lone pairs remain visible. Inner-shell electrons are omitted. These simple Lewis structures teach electron accounting, not the quantum description of bonding.
- Covalent bond
- A bond formed by a shared pair of electrons between atoms.
Carbon usually shares electrons in the compounds studied here. A single covalent bond is one shared pair; double and triple bonds contain two and three shared pairs.
Methane has four C—H bonds. Many small molecular compounds melt or boil relatively easily because attractions between molecules are weaker than the bonds inside each molecule.
Go deeper: Strong bonds, weaker attractions
Melting ethanol separates molecules; it does not split every C—H or O—H bond. This explains why a molecular liquid can boil while its molecules remain chemically intact.
Diamond and graphite are extended carbon structures, so the small-molecule explanation is not universal. Graphite conducts through mobile electrons; a covalent substance is not automatically an electrical insulator.
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Question
A sketch of O₂ shows four shared electrons and four unshared electrons around each O. How many valence electrons does each oxygen count?
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The Versatile Nature of Carbon
Connect carbon’s bonding capacity to chains, rings and different structural forms.BUILD · CHANGE · EXPLAIN
Four bonds let carbon build many shapes.
Compare: how does increasing C—C bond order change the hydrogen count?
Ethane · C₂H₆ · saturated
Count bond lines at each carbon: always four. A double bond uses two of carbon’s four valencies; a triple bond uses three.
Same carbon. Different architecture.
Predict: which structure lets layers slide, and which makes a rigid network?
One central carbon and its four tetrahedral neighbours. Bonds continue through a 3D network; this is a local fragment, not a diamond molecule. Rotation changes the view, not the bonds.
- Catenation
- An element bonding to its own atoms to form chains or other structures.
- Tetravalency
- Combining capacity of four; count a double bond as two and a triple bond as three.
| Property | Meaning | What it allows |
|---|---|---|
| Catenation | Carbon bonds to carbon | Chains, branches and rings |
| Tetravalency | Combining capacity of four; multiple bonds count more than once | Different structures while each carbon keeps total bond order four |
Catenation means carbon bonding to carbon. Tetravalency means a total bond order of four in these structures: a double bond counts twice and a triple bond three times.
Ethane, ethene and ethyne have different hydrogen counts. Diamond, graphite and fullerene are forms of carbon with different arrangements; graphite has layers, while diamond has a rigid three-dimensional network.
Go deeper: Same element, different structure
In diamond each carbon has four neighbours; in graphite each carbon has three neighbours in a layer, with electrons able to move through the layer. Layers can slide, helping explain graphite’s slippery feel.
C₆₀ is a closed cage of 60 carbon atoms. These allotropes are elemental carbon, whereas methane and ethanol are compounds containing carbon and other elements. Carbon is exceptional in the extent of catenation; it is not the only element able to link to itself.
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Question
A carbon has a triple bond to another carbon and a single bond to H. Is its valency unsatisfied?
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Chains, Branches, and Structural Isomers
Distinguish a changed drawing from changed connectivity, and compare saturated and unsaturated rings.BUILD · CHANGE · EXPLAIN
Same formula. Different connections.
Predict: which changes connectivity, and which only changes how a structure is drawn?
C₄H₁₀ · same molecular formula, different carbon skeleton
The branched molecule is not just straight butane bent on the page: a carbon is connected to three carbons instead of two.
- Structural isomers
- Compounds with the same molecular formula but different atom connectivity.
- Hydrocarbon
- A compound containing only carbon and hydrogen.
Straight butane and 2-methylpropane both contain four C and ten H atoms but connect the carbons differently. These are structural isomers; merely bending a drawing does not create an isomer.
Cyclohexane has six CH₂ groups joined by single bonds. Benzene has six CH groups in a ring; the chapter represents its bonding with alternating single and double lines.
Structural Isomers of Butane
C₄H₁₀Butane can be arranged as n-butane (CH₃-CH₂-CH₂-CH₃) or as isobutane (CH₃-CH(CH₃)-CH₃). Both contain 4 carbons and 10 hydrogens but have different connectivity.
Go deeper: A ring changes the hydrogen count
An open-chain alkane has formula CₙH₂ₙ₊₂. Closing a single-bond ring uses two of the valencies that would otherwise bond to hydrogen, giving CₙH₂ₙ for a monocyclic cycloalkane.
Cyclohexane is therefore saturated despite sharing CₙH₂ₙ with open-chain monoalkenes. Molecular formula alone does not decide the bond pattern. Benzene’s alternating drawing is a school representation; its electrons are delocalised around the ring.
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Question
A six-carbon molecule has twelve H atoms. A student labels it an alkene immediately. What other structure should they consider?
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Functional Groups and Homologous Series
Identify the group that stays the same as a homologous chain grows.BUILD · CHANGE · EXPLAIN
Keep the group. Extend the carbon chain.
Predict: what stays the same when one CH₂ is added?
Other hydrogens are omitted in this carbon skeleton. Each new member of the same series adds CH₂: 12 + 2 × 1 = 14 u. The functional group stays the same.
See the 14 u steps
Move the carbon slider: the highlighted molecule gains CH₂ at each step. The graph compares molecular masses, not boiling points or reaction speeds.
- Functional group
- An atom or group of atoms responsible for characteristic chemical reactions in a compound.
- Homologous series
- A family with the same functional group and general formula, whose successive members differ by CH₂.
| Class | Group | Look for |
|---|---|---|
| Haloalkane | —Cl / —Br | Halogen replacing H |
| Alcohol | —OH | O—H on a carbon chain |
| Aldehyde | —CHO | Terminal carbonyl bonded to H |
| Ketone | >C=O | Carbonyl between carbons |
| Carboxylic acid | —COOH | Carbonyl and OH on the same carbon |
Alcohols contain —OH, aldehydes —CHO, ketones an internal >C=O group and carboxylic acids —COOH. Halogen-containing compounds can have —Cl or —Br replacing a hydrogen.
Within one homologous series, successive members differ by CH₂ and 14 u. Similar functional groups give similar characteristic reactions, while physical properties change with chain length.
Go deeper: The carbonyl carbon counts
The C in —CHO or —COOH belongs to the carbon chain. A ketone needs a carbon on each side of C=O, so its simplest member has three carbons.
Similar chemical behaviour does not mean identical solubility, boiling point or every reaction rate. The formulae shown apply to the simple unbranched, single-group series in this chapter.
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Question
Two successive alcohols have molecular masses 46 u and 60 u. What unit accounts for the increase?
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Naming Carbon Compounds (Nomenclature)
Build a simple compound name from its carbon chain, bonds and functional group.BUILD · CHANGE · EXPLAIN
Read the structure to build its name.
Try naming the structure before revealing the ending.
The chain length supplies the root; the group supplies the ending. In propanone, the carbonyl carbon still counts as one of the three carbons.
- Nomenclature
- A systematic way of naming compounds from their structures.
Count the longest relevant carbon chain and identify the group. Meth-, eth-, prop- and but- represent one, two, three and four carbons; include the carbon in an aldehyde or acid group.
Use -ane, -ene or -yne for the simple hydrocarbon bond pattern. Alcohol, aldehyde, ketone and acid endings are -ol, -al, -one and -oic acid; chloro- and bromo- are prefixes.
Go deeper: Structure before suffix
For a three-carbon ketone, propane loses its final e before -one: propanone. The carbonyl carbon is one of those three carbons, not an extra group outside the chain.
More complicated examples require position numbers. The preview uses structures whose positions are unambiguous; it does not suggest that every alcohol with four carbons has only one possible structure.
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Question
CH₃—CH₂—CHO is called ethanal because it has two CH groups before CHO. Locate the counting error.
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