Chemical Bonding — Part 2: Covalent, polar and coordinate bonds: visual lesson, ICSE Class 10 Chemistry (Science Paper 2)

Lesson

Sharing instead of giving

Part 2 — when neither atom will give up electrons, they share pairs of electrons: the covalent bond.

In this lesson you will

Draw electron dot structures of H₂, Cl₂, O₂, N₂, CH₄ and CCl₄
Explain polar bonds in HCl, H₂O and NH₃ using electronegativity
Compare electrovalent and covalent compounds
Show the formation of H₃O⁺ and NH₄⁺ by coordinate bonds

Table of hydrogen, chlorine, oxygen and nitrogen molecules with their numbers of shared pairs
Molecule	Shared pairs	Bond
H₂, Cl₂	1	Single
O₂	2	Double
N₂	3	Triple

Diagram

Covalent bonds: single, double and triple

A covalent bond is formed by sharing a pair of electrons, each atom contributing one. H₂: one shared pair gives each H a duplet. Cl₂: one shared pair (single bond) completes both octets. O₂: two shared pairs (double bond). N₂: three shared pairs (triple bond). CH₄: carbon shares one pair with each of four H atoms. CCl₄: the same, with four Cl atoms. Unshared pairs on an atom are lone pairs.

Concept

Non-polar molecules

When two identical atoms share a pair (H₂, Cl₂, O₂, N₂), the pair is shared equally: the bond is non-polar. CH₄ and CCl₄ contain bonds between different atoms, but the four bonds point symmetrically to the corners of a tetrahedron, so their effects cancel and the molecules are non-polar overall.

Table of chlorine, methane and carbon tetrachloride showing why each molecule is non-polar
Molecule	Bonds	Shape	Polarity of molecule
Cl₂	Cl–Cl (identical atoms)	Linear	Non-polar
CH₄	4 C–H	Tetrahedral	Non-polar (symmetrical)
CCl₄	4 C–Cl (polar bonds)	Tetrahedral	Non-polar (effects cancel)

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