ICSE • Class 10 • Chemistry
Organic Chemistry
Introduction to carbon compounds, homologous series, and simple nomenclature.
Chapter 9
Verified Curriculum Topic
What is Organic Chemistry?
Introduction to carbon compounds, homologous series, and simple nomenclature.
Organic Chemistry matters because it links chemical ideas, reactions, and reasoning patterns that recur throughout the syllabus. At Class 10 level, students are often expected to define terms accurately, explain processes clearly, and connect theory to reactions, observations, or applications.
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Summary
The One Thing
Carbon forms an exceptionally wide range of compounds because tetravalency enables it to form four covalent bonds, while catenation enables carbon atoms to link into chains, branches, and rings. These compounds are organised into homologous series and named systematically according to their carbon chains, bond types, and functional groups.
Reactions, Processes and Experiments
| What happens | Equation or process | What you observe | Type |
|---|---|---|---|
| Carbon forms bonds with hydrogen and many other elements. | Carbon has atomic number 6 and electronic configuration 2,4; it generally forms covalent compounds rather than losing or gaining four electrons. | — | Covalent bonding |
| Carbon atoms bond to one another to form straight chains, branched chains, and rings. | Catenation: carbon atoms form carbon–carbon chains, branches, and rings. | — | Structural property |
| Carbon forms single, double, or triple covalent bonds. | The four covalent bonds of carbon may be single, double, or triple bonds. | — | Covalent bonding |
| Saturated hydrocarbons contain only single carbon–carbon bonds. | Alkanes have the general formula CnH2n+2. | — | Saturated hydrocarbon |
| Unsaturated hydrocarbons contain carbon–carbon double bonds. | Alkenes containing one double bond have the general formula CnH2n. | — | Unsaturated hydrocarbon |
| Unsaturated hydrocarbons contain carbon–carbon triple bonds. | Alkynes containing one triple bond have the general formula CnH2n-2. | — | Unsaturated hydrocarbon |
| The first four members of the alkane series are identified by increasing carbon-chain length. | Methane, CH4; ethane, C2H6; propane, C3H8; and butane, C4H10. | — | Homologous series |
| The first members of the alkene series contain a carbon–carbon double bond. | Ethene, C2H4, and propene, C3H6. An alkene must contain at least two carbon atoms. | — | Homologous series |
| The first member of the alkyne series contains a carbon–carbon triple bond. | Ethyne, C2H2. | — | Homologous series |
| Successive members of a homologous series increase by one –CH2– unit. | Successive members differ by CH2 and therefore by a relative molecular mass of 14 u. | — | Homologous series |
| Members of a homologous series contain the same functional group. | A homologous series has the same functional group and general formula, with successive members differing by a -CH2- unit. | Similar chemical properties. | Homologous series |
| Physical properties change as molecular mass increases within a homologous series. | Boiling point, melting point, and density usually change gradually with increasing molecular mass. | Gradual changes in boiling point, melting point, and density. | Physical trend |
| A carbon compound burns in sufficient oxygen. | Combustion of a carbon compound in sufficient oxygen generally produces carbon dioxide, water, heat, and light. | Heat and light are produced; carbon dioxide and water are formed. | Combustion |
| A carbon compound burns with insufficient oxygen. | Incomplete combustion may produce carbon monoxide and soot, which are harmful pollutants. | Carbon monoxide and soot may be formed. | Incomplete combustion |
| Saturated carbon compounds react by replacing an atom or group. | Saturated compounds generally undergo substitution reactions. | — | Substitution |
| Unsaturated carbon compounds react by adding atoms across a multiple bond. | Unsaturated compounds commonly undergo addition reactions. | — | Addition |
| An organic compound is named by selecting its parent chain. | Select the longest continuous carbon chain as the parent chain. | — | IUPAC nomenclature |
| The parent chain is numbered according to the position of the most important structural feature. | Number the parent chain from the end nearest to a double bond, triple bond, or principal functional group. | — | IUPAC nomenclature |
| Carbon-chain length is represented by standard prefixes. | Meth-, eth-, prop-, but-, pent-, hex-, hept-, oct-, non-, and dec- represent 1 to 10 carbon atoms. | — | IUPAC nomenclature |
| Bond type is represented by the name suffix. | The suffix -ane indicates single bonds, -ene indicates a double bond, and -yne indicates a triple bond. | — | IUPAC nomenclature |
| Simple organic compounds are assigned systematic names based on their structures. | Examples include methane, ethene, ethanol, ethanal, propanone, and ethanoic acid. | — | IUPAC nomenclature |
Key Terms
- Organic compounds: Compounds mainly containing carbon, usually along with hydrogen, oxygen, nitrogen, sulphur, halogens, or phosphorus.
- Tetravalency: The ability of a carbon atom to form four covalent bonds because it has four electrons in its outer shell.
- Catenation: The ability of carbon atoms to bond with one another to form straight chains, branched chains, and rings.
- Covalent bond: A chemical bond formed by the sharing of electron pairs between atoms.
- Saturated hydrocarbon: A hydrocarbon containing only single carbon–carbon bonds; alkanes are examples.
- Unsaturated hydrocarbon: A hydrocarbon containing one or more carbon–carbon double or triple bonds; alkenes and alkynes are examples.
- Hydrocarbon: An organic compound made only of carbon and hydrogen.
- Alkane: A saturated hydrocarbon with the general formula CnH2n+2.
- Alkene: An unsaturated hydrocarbon containing at least one carbon–carbon double bond, with the general formula CnH2n for one double bond.
- Alkyne: An unsaturated hydrocarbon containing at least one carbon–carbon triple bond, with the general formula CnH2n-2 for one triple bond.
- Functional group: An atom or group of atoms that gives an organic compound its characteristic chemical properties.
- Homologous series: A family of organic compounds having the same functional group and general formula, in which successive members differ by a -CH2- unit.
- Isomerism: The existence of compounds with the same molecular formula but different structural arrangements.
- Molecular formula: A formula showing the actual number of atoms of each element in one molecule.
- Structural formula: A formula showing how atoms are arranged and bonded in a molecule.
- IUPAC nomenclature: A systematic method of naming organic compounds using rules based on the longest carbon chain, bonds, and functional groups.
- Alkyl group: A group formed by removing one hydrogen atom from an alkane; examples include methyl, CH3-, and ethyl, C2H5-.
- Common functional groups: Important groups include -OH for alcohols, -CHO for aldehydes, >C=O for ketones, -COOH for carboxylic acids, and -X for halo compounds.
Easily Confused
- Tetravalency and catenation: Tetravalency is carbon’s ability to form four covalent bonds; catenation is carbon’s ability to bond to other carbon atoms.
- Saturated and unsaturated hydrocarbons: Saturated hydrocarbons contain only single carbon–carbon bonds, whereas unsaturated hydrocarbons contain one or more double or triple bonds.
- Alkenes and alkynes: Alkenes contain at least one carbon–carbon double bond and follow CnH2n for one double bond; alkynes contain at least one carbon–carbon triple bond and follow CnH2n-2 for one triple bond.
- Molecular and structural formulae: A molecular formula gives the actual numbers of each type of atom, whereas a structural formula shows how the atoms are arranged and bonded.
- Chemical and physical properties in a homologous series: Members have similar chemical properties because they possess the same functional group, while physical properties such as boiling point, melting point, and density change gradually with molecular mass.
- Substitution and addition reactions: Saturated compounds generally undergo substitution, whereas unsaturated compounds commonly undergo addition.
- Complete and incomplete combustion: Combustion in sufficient oxygen produces carbon dioxide and water, whereas incomplete combustion may produce carbon monoxide and soot.
- Carbon chain and functional group: The functional group mainly determines characteristic chemical reactions, while the carbon chain influences physical properties.
What Gets Asked
- Questions may require an explanation of why carbon forms such a large number of compounds. Marks depend on identifying both tetravalency and catenation, not just carbon’s ability to bond.
- Questions may ask for the general formulae and examples of alkanes, alkenes, and alkynes. The relevant distinctions are CnH2n+2, CnH2n, and CnH2n-2 respectively.
- Questions may test the members of a homologous series and the difference between successive members. The required difference is CH2, corresponding to a relative molecular mass of 14 u.
- Questions may ask why members of a homologous series have similar chemical properties but gradually changing physical properties. The same functional group explains the chemical similarity, while increasing molecular mass explains the physical trend.
- Naming questions may require selection of the longest continuous carbon chain, numbering from the end nearest to a double bond, triple bond, or principal functional group, and use of the correct prefix and suffix.
- Combustion questions may distinguish sufficient from insufficient oxygen. Complete combustion produces carbon dioxide, water, heat, and light; incomplete combustion may produce carbon monoxide and soot.
Flashcards
Quick quiz
Why can carbon form such a large variety of compounds?
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- C9.1Define catenation and explain why carbon shows an exceptional ability to form long chains and rings.
- C9.2Define a homologous series and state the general characteristics shared by members of a homologous series.
- C9.3Distinguish between saturated hydrocarbons (alkanes) and unsaturated hydrocarbons (alkenes and alkynes).
- C9.4Apply IUPAC rules to name simple straight-chain hydrocarbons up to five carbon atoms.
- C9.5Draw structural (displayed) formulae for simple alkanes, alkenes, and alkynes given their molecular formula.
- C9.6Describe simple chemical tests to distinguish between a saturated and an unsaturated hydrocarbon.
Practice questions
Q1. Bromine water is shaken with an unknown hydrocarbon and turns colourless. The hydrocarbon is most likely:1 mark · core
- A. An alkane
- B. An alkene
- C. A noble gas
- D. Water
Answer: B
- • 1 mark for selecting B
Alkenes contain a C=C double bond and rapidly decolourise bromine water through an addition reaction; saturated alkanes do not react with bromine water in this way under normal conditions.
Q2. Define catenation, and explain why carbon shows this property to an exceptional degree compared to other elements.2 marks · core
Answer: Catenation is the ability of atoms of an element to form bonds with other atoms of the same element, creating chains or rings. Carbon shows this to an exceptional degree because it has a small atomic size and forms strong, stable carbon-carbon covalent bonds, allowing it to form very long chains and rings, unlike most other elements.
- • 1 mark: correct definition of catenation as an element bonding to itself to form chains/rings
- • 1 mark: correct reasoning — carbon's small size and strong C-C bonds allow exceptional chain/ring formation
Q3. Distinguish between a saturated hydrocarbon and an unsaturated hydrocarbon, giving one example of each.2 marks · core
Answer: A saturated hydrocarbon contains only single covalent bonds between carbon atoms, for example ethane (C2H6). An unsaturated hydrocarbon contains at least one double or triple bond between carbon atoms, for example ethene (C2H4), which has a C=C double bond.
- • 1 mark: correct definition of saturated (only single C-C bonds) with a valid example
- • 1 mark: correct definition of unsaturated (at least one double/triple bond) with a valid example
Q4. Give the IUPAC name of the straight-chain alkane with the molecular formula C4H10.2 marks · core
Answer: Butane. The prefix "but-" indicates four carbon atoms, and the suffix "-ane" indicates it is a saturated alkane.
- • 1 mark: correct name, butane
- • 1 mark: correct reasoning linking the prefix/suffix to the carbon count and saturation
Key ideas to master
- Learn the precise terms, laws, and reaction patterns associated with Organic Chemistry.
- Understand why each step or change happens instead of memorising the result only.
- Practise writing balanced equations, comparisons, or structured explanations where relevant.
- Revise common exceptions, observations, and applications that examiners often test.
Common exam prompts
- Define the main idea in Organic Chemistry using correct chemical terminology.
- Write or interpret the reactions, observations, or comparisons that belong to this topic.
- Explain why a process happens, not just what happens.
- Summarise the high-yield facts and exceptions examiners often choose from this chapter.
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What is Organic Chemistry in ICSE Class 10 Chemistry?
Introduction to carbon compounds, homologous series, and simple nomenclature.
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