Organic Chemistry — Part 1: Carbon, bonds and carbon chains: visual lesson, ICSE Class 10 Chemistry (Science Paper 2)

Lesson

Why a whole branch for one element?

Part 1 — Organic chemistry is the chemistry of carbon compounds (except a few simple ones such as CO₂ and carbonates). More than ten million are known: fuels, plastics, medicines, foods and the molecules of living cells. Two properties of the carbon atom explain this huge number.

In this lesson you will

Explain tetravalency and catenation and why they give carbon so many compounds
Draw single, double and triple carbon–carbon bonds
Classify a carbon chain as straight, branched or cyclic and draw benzene
Write structural formulae of alkanes, alkenes and alkynes with up to five carbon atoms

Concept

Tetravalency

Carbon (atomic number 6) has the configuration 2, 4. To reach an octet it would have to lose or gain four electrons, which needs too much energy, so it shares its four valence electrons. Carbon therefore forms four covalent bonds: it is tetravalent. In methane, CH₄, the four bonds point to the corners of a regular tetrahedron.

Table of carbon, nitrogen, oxygen and hydrogen with their configurations and the number of covalent bonds each forms
Atom	Configuration	Electrons shared to complete the shell	Bonds formed
Carbon	2, 4	4	4
Nitrogen	2, 5	3	3
Oxygen	2, 6	2	2
Hydrogen	1	1 (duplet)	1

Concept

Catenation

Catenation is the ability of atoms of an element to link with one another by covalent bonds to form long chains, branched chains and rings. Carbon shows it far more than any other element, because carbon atoms are small and the C–C bond is strong. With four bonds per atom, every carbon in a chain still has bonds left over for hydrogen or other atoms.

Table of carbon compounds with chains of increasing length and where they are found
Compound	Carbon atoms linked	Where you meet it
Methane	1	Biogas, CNG
Propane and butane	3 and 4	LPG cylinders
Octane	8	Petrol
Paraffin wax	about 20 to 30	Candles

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