Carbon and Its Compounds
CLASS X · STRUCTURAL FORMULAE & NOMENCLATURE · PRACTICE SHEET
Section A — Drawing Structural Formulae
Q1. Draw the electron dot structure and structural formula of methane (CH₄).
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Methane has one carbon atom forming four single covalent bonds with four hydrogen atoms.
\[
\text{H} – \underset{\displaystyle \big| }{\overset{\displaystyle \text{H}}{\text{C}}} – \text{H} \quad \text{with a fourth H below the C}
\]
Structural formula: CH₄, with C at the centre bonded to 4 H atoms by 4 single bonds (tetrahedral arrangement)
Q2. Write the structural formula of ethane (C₂H₆) and identify the number of covalent bonds present.
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\[
\text{H}_3\text{C} – \text{CH}_3
\]
Ethane contains 1 C–C bond and 6 C–H bonds, making a total of 7 covalent bonds.
Q3. Draw the structural formula of ethene (C₂H₄) and ethyne (C₂H₂). State the type of bond between the two carbon atoms in each.
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Ethene:
\[
\text{H}_2\text{C} = \text{CH}_2
\]
— carbon atoms joined by a double bond.
Ethyne: \[ \text{HC} \equiv \text{CH} \] — carbon atoms joined by a triple bond.
Ethyne: \[ \text{HC} \equiv \text{CH} \] — carbon atoms joined by a triple bond.
Q4. Draw the structural formula of propane, and show all the possible structural isomers of butane (C₄H₁₀).
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Propane:
\[
\text{CH}_3 – \text{CH}_2 – \text{CH}_3
\]
Butane has two structural isomers:
n-butane (straight chain): \[ \text{CH}_3 – \text{CH}_2 – \text{CH}_2 – \text{CH}_3 \] 2-methylpropane / isobutane (branched chain): \[ \text{CH}_3 – \underset{\displaystyle \text{CH}_3}{\text{CH}} – \text{CH}_3 \] (the central carbon bears a methyl branch)
n-butane (straight chain): \[ \text{CH}_3 – \text{CH}_2 – \text{CH}_2 – \text{CH}_3 \] 2-methylpropane / isobutane (branched chain): \[ \text{CH}_3 – \underset{\displaystyle \text{CH}_3}{\text{CH}} – \text{CH}_3 \] (the central carbon bears a methyl branch)
Q5. Draw the structural formulae of ethanol (C₂H₅OH) and ethanoic acid (CH₃COOH), clearly showing the functional group in each.
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Ethanol (functional group: –OH, alcohol):
\[
\text{CH}_3 – \text{CH}_2 – \text{OH}
\]
Ethanoic acid (functional group: –COOH, carboxylic acid):
\[
\text{CH}_3 – \text{C}(=\text{O}) – \text{OH}
\]
Section B — IUPAC Nomenclature
Q6. Write the IUPAC names of the following compounds: (a) CH₃–CH₂–CH₂–CH₃ (b) CH₃–CH₂–OH (c) CH₃–CHO (d) CH₃–CO–CH₃
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(a) Butane
(b) Ethanol
(c) Ethanal
(d) Propanone
(b) Ethanol
(c) Ethanal
(d) Propanone
Q7. Name the functional groups present in the following compounds and give the general formula of each homologous series: (a) alcohols (b) aldehydes (c) ketones (d) carboxylic acids
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(a) Alcohol — functional group –OH; general formula \( \text{C}_n\text{H}_{2n+1}\text{OH} \)
(b) Aldehyde — functional group –CHO; general formula \( \text{C}_n\text{H}_{2n+1}\text{CHO} \)
(c) Ketone — functional group \(>\!\text{C}=\text{O}\); general formula \( \text{C}_n\text{H}_{2n+1}\text{CO}\text{C}_m\text{H}_{2m+1} \)
(d) Carboxylic acid — functional group –COOH; general formula \( \text{C}_n\text{H}_{2n+1}\text{COOH} \)
(b) Aldehyde — functional group –CHO; general formula \( \text{C}_n\text{H}_{2n+1}\text{CHO} \)
(c) Ketone — functional group \(>\!\text{C}=\text{O}\); general formula \( \text{C}_n\text{H}_{2n+1}\text{CO}\text{C}_m\text{H}_{2m+1} \)
(d) Carboxylic acid — functional group –COOH; general formula \( \text{C}_n\text{H}_{2n+1}\text{COOH} \)
Q8. Write the structural formula for: (a) propanal (b) pentan-1-ol (c) but-2-ene (d) propyne
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(a) Propanal: \( \text{CH}_3 – \text{CH}_2 – \text{CHO} \)
(b) Pentan-1-ol: \( \text{CH}_3 – \text{CH}_2 – \text{CH}_2 – \text{CH}_2 – \text{CH}_2\text{OH} \)
(c) But-2-ene: \( \text{CH}_3 – \text{CH} = \text{CH} – \text{CH}_3 \)
(d) Propyne: \( \text{CH}_3 – \text{C} \equiv \text{CH} \)
(b) Pentan-1-ol: \( \text{CH}_3 – \text{CH}_2 – \text{CH}_2 – \text{CH}_2 – \text{CH}_2\text{OH} \)
(c) But-2-ene: \( \text{CH}_3 – \text{CH} = \text{CH} – \text{CH}_3 \)
(d) Propyne: \( \text{CH}_3 – \text{C} \equiv \text{CH} \)
Q9. Differentiate between saturated and unsaturated hydrocarbons with one structural example each, and state the general formula for each class (alkanes, alkenes, alkynes).
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Saturated hydrocarbons (alkanes) contain only single bonds between carbon atoms.
General formula: \( \text{C}_n\text{H}_{2n+2} \) e.g. ethane, \( \text{CH}_3-\text{CH}_3 \)
Unsaturated hydrocarbons contain at least one double or triple bond.
Alkenes: \( \text{C}_n\text{H}_{2n} \) e.g. ethene, \( \text{H}_2\text{C}=\text{CH}_2 \)
Alkynes: \( \text{C}_n\text{H}_{2n-2} \) e.g. ethyne, \( \text{HC}\equiv\text{CH} \)
General formula: \( \text{C}_n\text{H}_{2n+2} \) e.g. ethane, \( \text{CH}_3-\text{CH}_3 \)
Unsaturated hydrocarbons contain at least one double or triple bond.
Alkenes: \( \text{C}_n\text{H}_{2n} \) e.g. ethene, \( \text{H}_2\text{C}=\text{CH}_2 \)
Alkynes: \( \text{C}_n\text{H}_{2n-2} \) e.g. ethyne, \( \text{HC}\equiv\text{CH} \)
Q10. Draw all possible isomers of pentane (C₅H₁₂) and give their IUPAC names.
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n-pentane:
\[
\text{CH}_3 – \text{CH}_2 – \text{CH}_2 – \text{CH}_2 – \text{CH}_3
\]
2-methylbutane:
\[
\text{CH}_3 – \underset{\displaystyle \text{CH}_3}{\text{CH}} – \text{CH}_2 – \text{CH}_3
\]
2,2-dimethylpropane (neopentane):
\[
\text{CH}_3 – \underset{\displaystyle \text{CH}_3}{\underset{\displaystyle |}{\text{C}}} – \text{CH}_3, \text{ with a second } \text{CH}_3 \text{ also on the central C}
\]
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