Carbon and Its Compounds

Class 10 CBSE Science • Easy, colourful notes for kids

Importance Covalent bond Why carbon? Naming Homologous series Isomers Reactions Ethanol & Ethanoic acid Soaps Revision

1. Importance of Carbon

Carbon is everywhere around us! It forms covalent compounds. Our body, plants, food, clothes, medicines, fuels (petrol, LPG, CNG), plastics and paper all have carbon.

Our body

about 18% carbon

Plants & food

sugar, starch, oil

Clothes

cotton, nylon, polyester

Fuels

petrol, diesel, LPG

Medicines

and soaps, plastics

Graphite and diamond: both are made of only carbon

2. Covalent Compounds

Covalent bond: a bond formed by sharing of electrons between two atoms. It is formed between non-metal + non-metal (C, S, N, O, H, Cl, F, Br).

Examples: H₂, O₂, N₂, Cl₂, H₂O (water), NH₃ (ammonia), CH₄ (methane).

● blue dot = electron of one atom | ✖ red cross = electron of the other atom

Formation of Cl₂ — single bond

Cl (17) = 2, 8, 7. Each Cl needs 1 more electron, so they share 1 pair.

Cl–Cl single covalent bond

Formation of O₂ — double bond

O (8) = 2, 6. Each O needs 2 more electrons, so they share 2 pairs.

O=O double covalent bond

Formation of N₂ — triple bond

N (7) = 2, 5. Each N needs 3 more electrons, so they share 3 pairs.

N≡N triple covalent bond

Formation of H₂O (water)

O (8) = 2, 6 and H (1) = 1. O shares with 2 hydrogens, so there are 2 single bonds.

H–O–H

Formation of CH₄ (methane)

C (6) = 2, 4 and H (1) = 1. C shares with 4 hydrogens, so there are 4 single bonds.

Methane, CH₄

Properties of covalent compounds

Poor conductors of electricity, because they have no ions (no charged particles).
Low melting and boiling points, because the forces between molecules (intermolecular forces) are weak.

Note: The covalent bond inside a molecule is strong, but the intermolecular forces between molecules are weak.

3. Why does Carbon form Covalent Compounds?

Carbon: atomic number 6 → electron arrangement 2, 4. It has 4 electrons in its outer shell. To get the noble gas (octet) configuration, it has two options:

Option 1: Lose 4 e⁻ (C⁴⁺)

Needs a LOT of energy, since 6 protons in the nucleus will pull the electrons strongly. Not possible

Option 2: Gain 4 e⁻ (C⁴⁻)

Difficult to hold 10 electrons with only 6 protons in the nucleus. Not possible

So carbon shares 4 electrons and always forms covalent bonds and covalent compounds

4. Naming (IUPAC Nomenclature)

Valency of carbon = 4 (tetra-valent). C (6) = 2, 4. Carbon can make 4 bonds.

Rule: count the carbon atoms

Carbons	Word root	Carbons	Word root
1	Meth	6	Hex
2	Eth	7	Hept
3	Prop	8	Oct
4	But	9	Non
5	Pent	10	Dec

Tip: To write a structure, first put the carbon chain. Then fill each carbon with hydrogens until every carbon has 4 bonds. For the name, remove the last ‘e’ of the name and add the suffix of the functional group (for example, propane → propan + ol = propanol).

🔗 5. Homologous Series, Functional Groups

Homologous series: a series of compounds with the same functional group, the same general formula and similar chemical properties, where each consecutive member differs by –CH₂ (mass of 14 u).

Alkanes (single bond, suffix –ane) — C_nH_2n+2

Name	Formula	Structure
Methane	CH₄	CH₄
Ethane	C₂H₆	CH₃–CH₃
Propane	C₃H₈	CH₃–CH₂–CH₃
Butane	C₄H₁₀	CH₃–CH₂–CH₂–CH₃
Pentane	C₅H₁₂	CH₃–CH₂–CH₂–CH₂–CH₃

Alkenes (double bond C=C, suffix –ene) — C_nH_2n

Name	Formula	Structure
Ethene	C₂H₄	CH₂=CH₂
Propene	C₃H₆	CH₂=CH–CH₃
Butene	C₄H₈	CH₂=CH–CH₂–CH₃

Alkynes (triple bond C≡C, suffix –yne) — C_nH_2n−2

Name	Formula	Structure
Ethyne	C₂H₂	CH≡CH
Propyne	C₃H₄	CH₃–C≡CH
Butyne	C₄H₆	CH₃–CH₂–C≡CH

Saturated = only single bonds (alkanes, less reactive, give a clean blue flame). Unsaturated = double or triple bonds (alkenes and alkynes, more reactive, give a yellow sooty flame).

Functional Groups

An atom or group of atoms that gives special chemical properties to a compound. Prefix: Cl = chloro, Br = bromo.

Name	Group	Suffix / Prefix	Formula	Examples
Halo (chloro/bromo)	–Cl, –Br	chloro-, bromo- (prefix)	C_nH_2n+1X	Chloromethane CH₃Cl, Chloroethane C₂H₅Cl, Chloropropane C₃H₇Cl
Alcohol	–OH	ol	C_nH_2n+1OH	Methanol CH₃OH, Ethanol C₂H₅OH, Propanol C₃H₇OH
Aldehyde	–CHO	al	C_nH_2nO	Methanal HCHO, Ethanal CH₃CHO, Propanal C₂H₅CHO
Ketone	>C=O	one	C_nH_2nO	Propanone CH₃COCH₃, Butanone CH₃COCH₂CH₃
Carboxylic acid	–COOH	oic acid	C_nH_2n+1COOH	Methanoic acid HCOOH, Ethanoic acid CH₃COOH

Aldehyde vs Ketone: Aldehyde (–CHO) is always at the END of the chain, and its 1st member has 1 carbon. Ketone (>C=O) is in the MIDDLE, between two carbons, so it needs at least 3 carbons. Both have the same formula C_nH_2nO.

Summary table

Name	IUPAC	Group	General formula
Alkane	ane	C–C	C_nH_2n+2
Alkene	ene	C=C	C_nH_2n
Alkyne	yne	C≡C	C_nH_2n−2
Alcohol	ol	–OH	not required
Aldehyde	al	–CHO	C_nH_2nO
Ketone	one	>C=O	C_nH_2nO
Carboxylic acid	oic acid	–COOH	not required

Electron dot structures of ethane and ethene

Ethane C₂H₆: H–C–C–H with 3 H on each C. All bonds are single (7 shared pairs).
Ethene C₂H₄: H₂C=CH₂. The carbons share 2 pairs (double bond), with 2 H on each C.

Properties of a homologous series

Molecular mass increases by 14 u as we go up the series.
Melting and boiling points increase going up (bigger molecules).
Solubility decreases as molecular mass increases. All physical properties show gradation (a slow change).
Chemical properties are the same for all members, because the functional group stays the same.

Atomic masses to remember: C = 12, H = 1, O = 16, N = 14, S = 32

6. Isomers

Isomers are compounds with the same molecular formula but different structural formulas.

Butane (C₄H₁₀) — 2 isomers

n-butane: CH₃–CH₂–CH₂–CH₃ (straight chain)
iso-butane: CH₃–CH(CH₃)–CH₃ (branched chain)

Pentane (C₅H₁₂) — 3 isomers

n-pentane: CH₃–CH₂–CH₂–CH₂–CH₃
iso-pentane: CH₃–CH(CH₃)–CH₂–CH₃
neo-pentane: C(CH₃)₄ (one carbon in the middle with 4 CH₃)

Aldehyde and ketone isomers (C₃H₆O)

Propanal (aldehyde): CH₃–CH₂–CHO
Propanone (ketone): CH₃–CO–CH₃

Tip: Butane has 2 isomers and pentane has 3. Hexane has 5, but that is not required in Class 10.

7. Chemical Reactions of Carbon Compounds

(a) Combustion of hydrocarbons

Complete combustion (plenty of air): products are CO₂ + H₂O + heat, with a clean blue flame.
Saturated carbon compounds (alkanes) generally give a clean blue flame (complete combustion).
Unsaturated carbon compounds give a yellow flame with lots of black smoke. A sooty deposit (unburnt carbon) forms on a metal plate, which is incomplete combustion.

CH₄ + 2O₂ → CO₂ + 2H₂O + heat and light

Note: In a limited supply of air, even saturated carbon compounds give a sooty flame, which is incomplete combustion.

(b) Substitution reaction

Occurs with saturated compounds. One H atom is replaced by another atom (like Cl).

CH₄ + Cl₂ —(sunlight)→ CH₃Cl + HCl (chloromethane)

➕ (c) Addition reaction

Occurs with unsaturated compounds (with a double or triple bond).

CH₂=CH₂ + H₂ —(Nickel or Palladium catalyst)→ CH₃–CH₃
Ethene (unsaturated) → Ethane (saturated)

Hydrogenation: addition of hydrogen to unsaturated compounds to give saturated compounds. It is used to turn vegetable oils (long unsaturated carbon chains) into vegetable ghee. Hydrogenated oils are more stable and less prone to oxidation and rancidity.

Saturated (Alkanes)	Unsaturated (Alkenes, Alkynes)
Only single bonds	Double or triple bond
Less reactive	More reactive
Show substitution reaction	Show addition reaction
Clean blue flame	Yellow sooty flame

Rings of carbon (cyclic compounds)

Carbon atoms can also join in a ring. Cyclic compounds can be saturated or unsaturated.

Cyclopropane C₃H₆

Cyclobutane C₄H₈

Cyclohexane C₆H₁₂ (saturated)

Benzene C₆H₆ (unsaturated)

Benzene (C₆H₆): 6 carbon atoms in a ring. It has 9 single bonds (6 C–H and 3 C–C) and 3 double bonds (C=C), and it is unsaturated.

Allotropy

Allotropy: the existence of an element in two or more forms (because of a different arrangement of atoms). The forms have different physical properties but identical chemical properties. The different forms of carbon are called allotropes, for example diamond and graphite.

Graphite

Smooth and slippery (used in pencils)

Diamond

Hardest natural substance

8. Ethanol and Ethanoic Acid

Ethanol (CH₃CH₂OH) — reactions

(1) With sodium (a metal) — ethanol reacts like an acid.

2CH₃CH₂OH + 2Na → 2CH₃CH₂ONa + H₂
Ethanol + Sodium → Sodium ethoxide + Hydrogen gas

Hydrogen gas burns with a pop sound. The reaction is vigorous with bubbles of hydrogen gas.

(2) Dehydration of ethanol (heating with excess conc. H₂SO₄ at 443 K)

CH₃CH₂OH —(conc. H₂SO₄, 443 K)→ CH₂=CH₂ + H₂O
Ethanol → Ethene + Water

Conc. H₂SO₄ is a dehydrating agent (it removes water), so this reaction is called dehydration of ethanol.

(3) Oxidation of ethanol to ethanoic acid

CH₃CH₂OH —(alkaline KMnO₄ or acidified K₂Cr₂O₇)→ CH₃COOH
Ethanol → Ethanoic acid (colourless)

Both alkaline KMnO₄ and acidified K₂Cr₂O₇ are oxidising agents. They add oxygen to ethanol, so this is oxidation.
The purple colour of alkaline KMnO₄ disappears.

Activity 4.5: Add alkaline KMnO₄ (potassium permanganate) drop by drop to warm ethanol.
Observation: the purple colour disappears. Reason: ethanol reacts with alkaline KMnO₄ to give ethanoic acid. On adding excess KMnO₄, the purple colour doesn’t disappear, as there is no ethanol left now.

Ethanoic acid (CH₃COOH) — also called Acetic acid

Commonly called acetic acid. Its 5–8% solution in water is vinegar, used as a preservative in pickles.
Glacial acetic acid: pure ethanoic acid. Its melting point is 290 K (17°C), so it often freezes in winter in cold climates.
Carboxylic acids are weak acids compared to HCl. The pH of acetic acid is about 2.4, and it turns universal indicator red to yellow.

Reactions of Ethanoic acid

(1) With a base (NaOH) → salt + water

CH₃COOH + NaOH → CH₃COONa + H₂O
(sodium ethanoate, a sodium salt)

(2) With metal carbonates and bicarbonates → salt + CO₂ + H₂O

2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂
CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂

Test for CO₂ gas: it turns lime water milky. The milkiness disappears on passing excess gas.

(3) Esterification — ethanoic acid + ethanol (with a little conc. H₂SO₄)

CH₃COOH + CH₃CH₂OH ⇄ CH₃COOCH₂CH₃ + H₂O
Acid + Alcohol ⇄ Ester (ethyl ethanoate) + Water

This is a reversible reaction. Esters are sweet-smelling substances, used in making perfumes and flavouring agents.

(4) Saponification — ester + NaOH → alcohol + soap

CH₃COOCH₂CH₃ + NaOH → CH₃CH₂OH + CH₃COONa (soap)

Remember: Reaction of an acid with an alcohol gives an ester (esterification). Reaction of an ester with a base (NaOH) gives soap (saponification).

9. Soaps and Detergents

Soaps are sodium or potassium salts of long-chain carboxylic acids (17–18 carbon atoms).

A soap molecule has two ends: a hydrophobic tail (hydro = water, phobic = fearing, so it likes oil) and a hydrophilic head (it likes water).

Micelles (pronounced “my-sell”)

Most of the dirt is oil. Soap tails go towards oil and heads stay towards water, forming a ball called a micelle.
The oil dirt is trapped inside the micelle.
It is washed away with water on rinsing.

Micelle diagram — A micelle with oil trapped inside

Soap and hard water

Hard water (khara pani, ground water, tube well) has calcium and magnesium salts.
Soap + hard water → no foam, and a scum (insoluble precipitate) forms.
Reaction: Na/K salt of carboxylic acid + Ca/Mg salts → insoluble precipitate.
So soaps are not effective with hard water. Dirt cannot be washed away, so detergents are used.

Soap	Detergent
Sodium salts of long-chain fatty acids	Sodium or potassium salts of sulphonic acids of hydrocarbons
Cannot be used with hard water	Work well with both hard and soft water
Do not give foam with hard water	Give foam with hard water
Form precipitate (scum) with salts in hard water	Do not form precipitate with hard water

Note: Detergents are also used for making shampoo and for cleaning clothes.

10. Quick Revision

Covalent bond

Sharing of electrons

Valency of C

4 (tetravalent)

Alkane

C_nH_2n+2, –ane

Alkene

C_nH_2n, –ene

Alkyne

C_nH_2n−2, –yne

Isomers

Same formula, different structure

Substitution

Saturated compounds

Addition

Unsaturated compounds

Esterification

Acid + Alcohol → Ester

Saponification

Ester + NaOH → Soap

Hydrogenation

Oil → Ghee (Ni catalyst)

Allotropes of C

Diamond, graphite

Order to remember: Meth, Eth, Prop, But, Pent, Hex, Hept, Oct, Non, Dec (1 to 10 carbons).

All the best for your exams!

class 10 chemistry: Carbon and its Compounds