What the board actually asks:draw electron-dot (Lewis) structures for simple covalent molecules (H2, O2, N2, CH4, CO2 and compounds such as CH3Cl); give the two reasons - catenation and tetravalency - for carbon's huge number of compounds; define a homologous series and give an example; name a compound and identify its functional group; write balanced equations for combustion, the oxidation of ethanol to ethanoic acid, addition (hydrogenation), substitution, esterification and saponification, with the correct conditions above the arrow; differentiate ethanol and ethanoic acid by their physical and chemical properties; and explain the cleaning action of soap through micelle formation. Most marks sit in drawing the correct structure and writing the right reaction with its conditions.
One element, millions of compounds - because carbon shares.
Carbon completes its octet not by giving or taking electrons but by sharing them, forming four strong covalent bonds. Two properties - catenation (carbon-to-carbon chains, branches and rings) and tetravalency - let carbon build an enormous family of compounds. Attach a functional group and a whole homologous series behaves alike, so learning one member teaches you the rest. The chapter's reactions - combustion, oxidation, addition, substitution, esterification and saponification - and the cleaning action of soap all follow from this covalent bonding.
Formulae
Covalent bond
shared electron pair between two atoms = 1 covalent bond (2 pairs = double, 3 pairs = triple)
Nomenclature of Carbon Compounds (Steps and Table)
(1) Count the carbon atoms and use the root word: meth (1), eth (2), prop (3), but (4), pent (5), hex (6). (2) Show the functional group as a prefix or a suffix: halo → prefix chloro-, bromo-; alcohol → suffix –ol; aldehyde → –al; ketone → –one. (3) If the suffix begins with a vowel, drop the final 'e' of the chain name (propane + ol → propanol). (4) A double bond is shown by –ene and a triple bond by –yne.
Electron Dot Structures
In a hydrogen molecule two atoms share one pair of electrons (a single bond); in oxygen they share two pairs (a double bond); in nitrogen three pairs (a triple bond). In methane, carbon shares four pairs, one with each of four hydrogen atoms. Valency: carbon 4, hydrogen 1, oxygen 2, nitrogen 3.
Properties of Covalent Compounds
Covalent compounds have low melting and boiling points and are poor conductors of electricity, because no ions are formed.
Soaps and Detergents: Cleansing Action
Soap is the sodium or potassium salt of a long-chain carboxylic acid. One end (ionic) is attracted to water; the long carbon chain is attracted to oil. In water the molecules form clusters called micelles, with the oily dirt collected in the middle, so the dirt is rinsed away. With hard water, soap reacts with calcium and magnesium salts to form an insoluble scum, so more soap is needed; detergents do not form scum.
Ethanol and Ethanoic Acid: Properties and Uses
Ethanol is a liquid at room temperature, dissolves in water, reacts with sodium and, heated with hot concentrated sulphuric acid, gives ethene. It is a good solvent, used in medicines such as tincture of iodine and cough syrups. Ethanoic acid reacts with bases, carbonates and hydrogencarbonates (releasing carbon dioxide). A 5–8% solution of ethanoic acid in water is vinegar, used as a preservative in pickles.
Allotropes of Carbon
Diamond and graphite are both forms (allotropes) of carbon. Diamond is the hardest natural substance known; graphite conducts electricity.
📖NCERT verbatim — memorise this exact wording· Ch 4,
“Such bonds which are formed by the sharing of an electron pair between two atoms are known as covalent bonds.”
What it means:A bond made by two atoms sharing a pair of electrons so that both attain a filled outer shell - no ions are formed, which is why carbon compounds are poor conductors.
Catenation
📖NCERT verbatim — memorise this exact wording· Ch 4,
“Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation.”
What it means:Carbon's ability to bond to other carbon atoms to build long chains, branched chains or rings; the strong C-C bond makes these compounds stable.
Saturated compounds
📖NCERT verbatim — memorise this exact wording· Ch 4,
“Compounds of carbon, which are linked by only single bonds between the carbon atoms are called saturated compounds.”
What it means:Carbon compounds with only single C-C bonds (the alkanes); they are generally not very reactive.
Unsaturated compounds
📖NCERT verbatim — memorise this exact wording· Ch 4,
“Compounds of carbon having double or triple bonds between their carbon atoms are called unsaturated compounds.”
What it means:Carbon compounds with at least one C=C or C-triple-C bond (alkenes and alkynes); they are more reactive than saturated compounds.
Hydrocarbons
📖NCERT verbatim — memorise this exact wording· Ch 4,
“All these carbon compounds which contain only carbon and hydrogen are called hydrocarbons.”
What it means:Compounds of only carbon and hydrogen; the saturated ones are alkanes, the unsaturated ones alkenes (double bond) or alkynes (triple bond).
Functional group
📖NCERT verbatim — memorise this exact wording· Ch 4,
“These heteroatoms and the group containing these confer specific properties to the compound, regardless of the length and nature of the carbon chain and hence are called functional groups.”
What it means:An atom or group of atoms (like -OH, -CHO, -COOH) that decides the chemical properties of the compound, whatever the length of the carbon chain.
Homologous series
📖NCERT verbatim — memorise this exact wording· Ch 4,
“Hence, such a series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homologous series.”
What it means:A family of compounds with the same functional group where each member differs from the next by a −CH2− unit (14 u); members share similar chemical properties and show a gradation in physical properties.
📖Key terms — NCERT verbatim (state word-for-word)
Single covalent bond
The shared pair of electrons is said to constitute a single covalent bond between the two hydrogen atoms. (Ch 4, )
Structural isomers
Such compounds with identical molecular formula but different structures are called structural isomers. (Ch 4, )
Substitution reaction
It is called a substitution reaction because one type of atom or a group of atoms takes the place of another. (Ch 4, )
Oxidising agents
We see that some substances are capable of adding oxygen to others. These substances are known as oxidising agents. (Ch 4, )
Saponification
This reaction is known as saponification because it is used in the preparation of soap. (Ch 4, )
Micelle
clusters of molecules in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface of the cluster. This formation is called a micelle. (Ch 4, )
Detergents
Detergents are generally sodium salts of sulphonic acids or ammonium salts with chlorides or bromides ions, etc. (Ch 4, )
Must-know concepts AUTHORED FRAMING
…and where they’re tested
1
Covalent bonding and electron-dot structures
Carbon has four valence electrons and cannot easily gain or lose four, so it shares them, forming four covalent bonds. Show only valence electrons as dots or crosses: a single shared pair is a single bond (H2, CH4), two shared pairs a double bond (O2), three shared pairs a triple bond (N2). Because no ions form, covalent compounds have low melting/boiling points and are poor conductors of electricity.
NCERT Fig 4.5Electron dot structure for methane (CH4).
Each of carbon's four valence electrons is shared with a hydrogen atom (a dot-and-cross pair per bond), giving four single covalent bonds and a completed octet for carbon.
3-mark: draw the electron dot structure of a given molecule (e.g. CH3Cl, CO2, ethanoic acid) and explain the covalent bonding.
2
Allotropes of carbon
Carbon occurs in different forms with the same chemistry but very different physical properties. In diamond each carbon is bonded to four other carbons in a rigid three-dimensional network, making it the hardest natural substance. In graphite each carbon is bonded to three others in hexagonal layers, so it is soft, slippery and (unusually for a non-metal) a good conductor. Fullerenes are a third class - C-60 has carbon atoms arranged in a football shape.
2-mark: compare the structure and one physical property of diamond and graphite; name the C-60 allotrope.
3
Versatile nature of carbon (catenation + tetravalency)
Two features explain why millions of carbon compounds exist. Catenation is carbon's ability to bond to other carbon atoms to form long chains, branched chains and rings; the C-C bond is strong and stable because carbon is small. Tetravalency means each carbon can bond to four other atoms - of carbon or of oxygen, hydrogen, nitrogen, sulphur, chlorine and more - giving compounds with many different properties.
2-mark: state the two properties of carbon that lead to the huge number of carbon compounds.
4
Chains, branches, rings and isomers
Saturated hydrocarbons (alkanes, methane to hexane) have only single bonds; unsaturated ones have double bonds (alkenes) or triple bonds (alkynes). Carbon skeletons can be straight chains, branched chains or rings (e.g. cyclohexane, benzene). From four carbons onward the same molecular formula can be arranged in more than one way - these are structural isomers (e.g. two isomers of butane, C4H10).
NCERT Table 4.2Formulae and structures of the first six saturated hydrocarbons (alkanes), methane to hexane.
Each successive member gains one −CH2− unit; the single-bonded carbon skeleton lengthens from CH4 to C6H14 - a homologous series.
3-mark: draw the structures/structural isomers of a named compound (e.g. the isomers of pentane) and classify as saturated or unsaturated.
5
Homologous series, functional groups and naming
Replacing a hydrogen on a carbon chain with a functional group (halo-, alcohol -OH, aldehyde, ketone, carboxylic acid) fixes the chemistry of the compound. A homologous series shares one functional group, with successive members differing by a −CH2− unit (14 u); chemical properties stay similar while melting/boiling points rise gradually. To name a compound: count the carbons for the stem (meth-, eth-, prop-, but-...), then add the group's prefix or suffix, dropping the final 'e' before a vowel suffix (propane - e + one = propanone).
3-mark: define a homologous series with an example; name compounds or identify the functional group from a formula.
6
Chemical properties of carbon compounds
Combustion: carbon and its compounds burn in oxygen to give carbon dioxide (and water) with heat and light; saturated hydrocarbons give a clean blue flame, unsaturated ones a sooty yellow flame. Oxidation: alcohols are oxidised to carboxylic acids by oxidising agents (alkaline KMnO4 or acidified K2Cr2O7). Addition: unsaturated hydrocarbons add hydrogen over a nickel/palladium catalyst (hydrogenation). Substitution: in sunlight, chlorine replaces the hydrogens of a saturated hydrocarbon one by one.
identify the reaction type from an equation; name the products; state which hydrocarbons undergo addition reactions.
7
Ethanol, ethanoic acid, soaps and detergents
Ethanol (alcohol) reacts with sodium to release hydrogen and, with hot concentrated sulphuric acid, dehydrates to ethene. Ethanoic acid (acetic acid, a weak carboxylic acid; its pure form is glacial acetic acid) forms an ester with ethanol (esterification), gives a salt and water with a base, and releases carbon dioxide with carbonates and hydrogencarbonates. Soaps are sodium/potassium salts of long-chain carboxylic acids; their molecules form micelles that trap oily dirt (ionic heads out, hydrocarbon tails in) so it rinses away, while detergents keep working even in hard water.
NCERT Fig 4.13A soap micelle (detail from the 'effect of soap in cleaning' figure).
The ionic, hydrophilic heads face outward into the water (the sodium-ion ends) while the hydrocarbon, hydrophobic tails point inward, trapping the oily dirt in the centre of the cluster.
3-mark: explain the cleaning action of soap via micelle formation; differentiate ethanol and ethanoic acid by their properties.
Worked examples — real solved problems NCERT VERBATIM
Solved exactly as the source does them
Every problem is a real sourced item, quoted verbatim with its page; the step-by-step decoding and mark-logic are LazyTopper-authored coaching.
Ch 4,
“[authored prompt] Write the balanced chemical equations for the complete combustion of (i) carbon, (ii) methane and (iii) ethanol in oxygen.”
1
Carbon.Carbon burns in oxygen to give carbon dioxide with heat and light:
C+O2→CO2+heat and light
Concept: combustion = oxidation
1 mark
2
Methane.Balancing the skeletal combustion equation printed in the chapter:
CH4+2O2→CO2+2H2O+heat and light
1 mark
3
Ethanol.Balancing the ethanol combustion equation; alcohol burns cleanly:
CH3CH2OH+3O2→2CO2+3H2O+heat and light
1 mark
Mark-scheme logic (authored):3-mark: one correct balanced combustion equation for each fuel - carbon (1), methane (1) and ethanol (1). All three are oxidation reactions that release heat and light.
Ch 4,
“[authored prompt] Why is the conversion of ethanol to ethanoic acid an oxidation reaction, and which reagent brings it about?”
Ch 4,
“[authored prompt] What is hydrogenation? Give the catalyst used and one industrial application.”
Ch 4,
“[authored prompt] Methane reacts with chlorine in the presence of sunlight. Write the equation and explain why it is called a substitution reaction.”
Ch 4,
“[authored prompt] Ethanoic acid is warmed with ethanol and a little concentrated sulphuric acid. Name the reaction and product, write the equation, and state what happens when the product is treated with sodium hydroxide.”
Ch 4,
“[authored prompt] How does ethanoic acid react with (i) sodium hydroxide and (ii) sodium carbonate? Write the balanced equations and name the gas evolved in (ii).”
Problem-solving strategies AUTHORED
→
Drawing an electron dot structure?Show only the valence electrons and give every atom a completely filled outer shell. Carbon is tetravalent, so it forms four shared pairs; one shared pair is a single bond, two pairs a double bond, three pairs a triple bond.
→
Naming a compound?First count the carbon atoms for the stem (meth-1, eth-2, prop-3, but-4...), then add the functional group as a prefix or suffix. Drop the final 'e' of the stem before a suffix beginning with a vowel (propane - e + one = propanone).
→
Which reaction type is it?Saturated + Cl2 in sunlight is substitution; unsaturated + H2 over Ni is addition; alcohol + oxidising agent is oxidation; acid + alcohol is esterification; ester + NaOH is saponification.
→
Cleaning action asked?Explain the soap molecule's two ends (an ionic hydrophilic head and a hydrocarbon hydrophobic tail), how micelles form around oily dirt, and how agitation lifts the emulsified dirt into the water so it rinses away.
Common mistakes that cost marks
Where students lose easy marks
✕
Changing subscripts instead of coefficients to balance a combustion equation - only the coefficients in front of a formula may be changed, never the subscripts inside it.
✕
Confusing addition (hydrogen adds across the double/triple bond of an unsaturated compound) with substitution (an atom replaces a hydrogen in a saturated compound).
✕
Forgetting to drop the final 'e' of the stem before a vowel suffix - e.g. writing 'propaneone' instead of propanone.
✕
Claiming a micelle forms in any solvent. It forms in water because one end is hydrophilic; in a pure hydrocarbon solvent no micelle forms.
✕
Calling ethanoic acid a strong acid. Carboxylic acids are weak acids and are only partially ionised, unlike mineral acids such as HCl.
Formulae
Covalent bond
shared electron pair between two atoms = 1 covalent bond (2 pairs = double, 3 pairs = triple)
Nomenclature of Carbon Compounds (Steps and Table)
(1) Count the carbon atoms and use the root word: meth (1), eth (2), prop (3), but (4), pent (5), hex (6). (2) Show the functional group as a prefix or a suffix: halo → prefix chloro-, bromo-; alcohol → suffix –ol; aldehyde → –al; ketone → –one. (3) If the suffix begins with a vowel, drop the final 'e' of the chain name (propane + ol → propanol). (4) A double bond is shown by –ene and a triple bond by –yne.
Electron Dot Structures
In a hydrogen molecule two atoms share one pair of electrons (a single bond); in oxygen they share two pairs (a double bond); in nitrogen three pairs (a triple bond). In methane, carbon shares four pairs, one with each of four hydrogen atoms. Valency: carbon 4, hydrogen 1, oxygen 2, nitrogen 3.
Properties of Covalent Compounds
Covalent compounds have low melting and boiling points and are poor conductors of electricity, because no ions are formed.
Soaps and Detergents: Cleansing Action
Soap is the sodium or potassium salt of a long-chain carboxylic acid. One end (ionic) is attracted to water; the long carbon chain is attracted to oil. In water the molecules form clusters called micelles, with the oily dirt collected in the middle, so the dirt is rinsed away. With hard water, soap reacts with calcium and magnesium salts to form an insoluble scum, so more soap is needed; detergents do not form scum.
Ethanol and Ethanoic Acid: Properties and Uses
Ethanol is a liquid at room temperature, dissolves in water, reacts with sodium and, heated with hot concentrated sulphuric acid, gives ethene. It is a good solvent, used in medicines such as tincture of iodine and cough syrups. Ethanoic acid reacts with bases, carbonates and hydrogencarbonates (releasing carbon dioxide). A 5–8% solution of ethanoic acid in water is vinegar, used as a preservative in pickles.
Allotropes of Carbon
Diamond and graphite are both forms (allotropes) of carbon. Diamond is the hardest natural substance known; graphite conducts electricity.
Shortcuts & Tricks
Alkane CₙH₂ₙ₊₂, alkene CₙH₂ₙ, alkyne CₙH₂ₙ₋₂; test with n = 2: C₂H₆, C₂H₄, C₂H₂.
Soap micelle. ionic end in water; hydrocarbon tail in oil.
Mindmap
Covalent bond = shared electron pair
H2, O2 (double), N2 (triple), CH4
Tetravalent - forms 4 bonds
Poor conductor; low m.p./b.p.
Diamond - each C bonded to 4 C (hardest)
Graphite - each C bonded to 3 C (conducts)
Fullerene - C-60, football shape
Catenation - C-C chains, branches, rings
Tetravalency - bonds four atoms
Millions of carbon compounds
Saturated (alkanes) - single bonds
Unsaturated - alkenes (=), alkynes (triple)
Structural isomers - same formula
Homologous series - differ by CH2
Halo, alcohol, aldehyde, ketone, carboxylic acid
Prefix/suffix nomenclature
Same group = similar chemistry
Combustion →CO2+H2O+heat
Oxidation: ethanol → ethanoic acid
Addition (hydrogenation, Ni)
Substitution (CH4+Cl2, sunlight)
Ethanol + Na→H2; dehydration → ethene
Ethanoic acid: ester, salt + CO2 with carbonate
Soap micelle - cleans oily dirt
Detergents work in hard water
For Chemistry the subject-adaptive third tab holds the chapter's key reactions - the formal core you must be able to reproduce, grouped by property. Every reaction is a real NCERT Ch 4 reaction; the condition sits above/beside the arrow. Where NCERT prints a skeletal equation and asks you to balance it, the balanced form is given and flagged.
1
Combustion - carbon
C+O2→CO2+heat and light
Carbon burns completely in oxygen; an oxidation reaction
2
Combustion - methane
CH4+2O2→CO2+2H2O+heat and light
Balanced form of the skeletal combustion equation printed on p.69
3
Combustion - ethanol
CH3CH2OH+3O2→2CO2+3H2O+heat and light
Balanced form of the skeletal combustion equation printed on p.69; alcohol burns cleanly
Alcohol oxidised to carboxylic acid; the oxidising agent adds oxygen
5
Addition - hydrogenation of unsaturated hydrocarbons
R-CH=CH-R’+H2NiR-CH2-CH2-R’
Unsaturated hydrocarbons add hydrogen over a Ni/Pd catalyst to give saturated hydrocarbons; used to harden vegetable oils (NCERT describes this reaction textually, p.71)
6
Substitution - methane and chlorine
CH4+Cl2SunlightCH3Cl+HCl
In sunlight chlorine replaces hydrogen atoms of the saturated hydrocarbon one by one
7
Ethanol with sodium
2Na+2CH3CH2OH→2CH3CH2ONa+H2
Alcohols react with sodium; hydrogen gas is evolved and sodium ethoxide is formed
8
Dehydration of ethanol to ethene
CH3CH2OHHot conc. H2SO4, 443 KCH2=CH2+H2O
Concentrated sulphuric acid acts as a dehydrating agent, giving the unsaturated ethene
9
Esterification
CH3COOH+CH3CH2OHAcidCH3COOC2H5+H2O
Acid + alcohol give a sweet-smelling ester (ethyl ethanoate) and water; acid catalyst
10
Saponification
CH3COOC2H5+NaOH→C2H5OH+CH3COONa
Ester + alkali give the alcohol and the sodium salt of the acid; the basis of soap-making
11
Ethanoic acid with a base
NaOH+CH3COOH→CH3COONa+H2O
Neutralisation; gives sodium ethanoate (sodium acetate) and water
12
Ethanoic acid with sodium carbonate
2CH3COOH+Na2CO3→2CH3COONa+H2O+CO2
Gives salt + water + carbon dioxide (turns lime-water milky)
13
Ethanoic acid with sodium hydrogencarbonate
CH3COOH+NaHCO3→CH3COONa+H2O+CO2
Gives salt + water + carbon dioxide
3 competency questions from the CBSE board pattern, with the full step-marked solution for each — the marks are shown per step, as the official scheme awards them.
5 marksSection D
A carbon compound P has six carbon atoms and twelve hydrogen atoms. (a) Is P a saturated or unsaturated carbon compound? Justify by drawing the structural formula. (b) Describe a test that can be used to determine if compound P is saturated or unsaturated. (c) Name the products formed on burning compound P in excess of air.
Step-marked solution
[1 mark] (a) C6H12 fits the general formula CnH2n, which is satisfied both by unsaturated alkenes (one C=C double bond) and by saturated cycloalkanes (a ring). So P may be saturated or unsaturated.
[1 mark] (a) Structures: unsaturated hexene CH3-CH=CH-CH2-CH2-CH3 (C4=C bond) and saturated cyclohexane (a six-membered ring of six CH2 groups).
[1 mark] (b) Burning test: an unsaturated compound burns with a sooty yellow flame (high C/H ratio), while a saturated compound burns with a clean blue flame.
[1 mark] (b) Bromine-water test: an unsaturated compound decolourises brown bromine water; a saturated compound does not.
[1 mark] (c) On complete combustion in excess air, any hydrocarbon gives carbon dioxide (CO2) and water (H2O).
4 marksSection E
Given a 4-carbon skeleton of a hydrocarbon compound. (a) Fill in the hydrogen atoms/bonds to form: (i) a saturated hydrocarbon (ii) an unsaturated hydrocarbon. (b) If the four-carbon skeleton is of a straight chained alkene, draw the structures of all the possible compounds.
Step-marked solution
[1 mark] (a)(i) Saturated hydrocarbon with 4 carbons: butane, CH3-CH2-CH2-CH3 (C4H10), with all single bonds.
[1 mark] (a)(ii) Unsaturated hydrocarbon: butene CH2=CH-CH2-CH3 (C4H8) with a C=C double bond (or butyne CH≡C-CH2-CH3, C4H6).
[1 mark] (b) First straight-chain alkene: But-1-ene, CH2=CH-CH2-CH3, with the double bond at position 1.
[1 mark] (b) Second straight-chain alkene: But-2-ene, CH3-CH=CH-CH3, with the double bond at position 2.
4 marksSection E
If the four-carbon skeleton is of a straight chained alkyne: (i) How many carbon atoms may NOT be bonded to any hydrogen atoms? (ii) How many hydrogen atoms will there be in the compound?
Step-marked solution
[1 mark] The straight-chain alkynes with 4 carbons are but-1-yne (HC≡C-CH2-CH3) and but-2-yne (CH3-C≡C-CH3), both C4H6.
[1 mark] (i) In but-1-yne, HC≡C-CH2-CH3: C1 has 1 H, C2 has 0 H, C3 has 2 H, C4 has 3 H → one carbon (C2) is bonded to no hydrogen.
[1 mark] (i) In but-2-yne, CH3-C≡C-CH3: C1 has 3 H, C2 has 0 H, C3 has 0 H, C4 has 3 H → two carbons (C2 and C3) are bonded to no hydrogen. So one or two carbons may not be bonded to any H.
[1 mark] (ii) The molecular formula is C4H6, so the compound contains six hydrogen atoms.