ChemistryICSE Class 10 · Chemical Bonding

Covalent Bonding: Electron Dot Structures, Polarity and Properties (ICSE Class 10)

Updated 17 October 2026 · Fact-checked

A covalent bond is formed when two atoms share one or more pairs of electrons so that each reaches a duplet (hydrogen) or an octet. If the atoms are identical, or the electronegativity difference is negligible, the molecule is non-polar (H₂, Cl₂, O₂, N₂, CH₄, CCl₄). If one atom attracts the shared pair more strongly, the bond is polar (HCl, NH₃, H₂O). Covalent compounds usually have low melting and boiling points and do not conduct electricity.

In Cl₂ the shared pair sits midway, so it is non-polar; in HCl chlorine pulls the pair closer, giving δ− on Cl and δ+ on H.

Illustration drawn for QuestionBuddy.

Understand Covalent Bonding, Polar and Non-polar Molecules

1. Formation. Non-metal atoms that cannot easily lose electrons share them. A single bond is one shared pair, a double bond two shared pairs and a triple bond three shared pairs. A pair that is shared is a bond pair; a pair on one atom that is not shared is a lone pair.

2. Non-polar covalent molecules (shared pair is equally attracted).

Hydrogen, H₂: each H has one electron; one shared pair gives both a duplet. H-H.
Chlorine, Cl₂: each Cl has seven outer electrons; one shared pair gives both an octet. Each Cl keeps three lone pairs.
Oxygen, O₂: each O has six outer electrons; two shared pairs (a double bond) give an octet to each. O=O with two lone pairs on each atom.
Nitrogen, N₂: each N has five outer electrons; three shared pairs (a triple bond) give an octet. Each N keeps one lone pair.
Methane, CH₄: carbon (2,4) shares one pair with each of four H atoms; four single bonds, no lone pair.
Carbon tetrachloride, CCl₄: carbon shares one pair with each of four Cl atoms; each Cl keeps three lone pairs.

CH₄ and CCl₄ are non-polar as molecules because the four identical bonds are arranged evenly around carbon.

3. Polar covalent molecules. Electronegativity is the tendency of an atom to attract the shared pair. When two different atoms share electrons, the one with higher electronegativity pulls the pair closer and gets a small negative charge (shown as $δ -$ ); the other gets $δ +$ .

HCl: chlorine is more electronegative; one bond pair, three lone pairs on Cl. H $δ +$ - Cl $δ -$ .
NH₃: nitrogen is more electronegative; three N-H bond pairs and one lone pair on N.
H₂O: oxygen is more electronegative; two O-H bond pairs and two lone pairs on O.

4. Properties of covalent compounds.

State: gases, liquids or soft solids; the forces between molecules are weak.
Melting and boiling points: low, since little energy is needed to separate the molecules.
Conductivity: poor conductors of heat and electricity (no free ions or electrons). A polar compound such as HCl ionises in water ( $H C l + H_{2} O \to H_{3} O^{+} + C l^{-}$ ) and then conducts.
Solubility: non-polar covalent compounds dissolve in organic solvents but not in water; many polar ones dissolve in water.

5. Electrovalent versus covalent.

Property	Electrovalent	Covalent
Formed by	transfer of electrons	sharing of electrons
State	hard crystalline solids	gases, liquids, soft solids
Melting and boiling points	high	low
Conduction	molten or in solution	non-conductors (polar ones ionise in water)
Solubility	water	organic solvents

Covalent Bonding, Polar and Non-polar Molecules: formulas and key facts

Bond count: $S in g l e b o n d = 1 s ha r e d p ai r ∣ D o u b l e b o n d = 2∣ T r i pl e b o n d = 3$
Bond pairs and lone pairs: H₂ 1 bond pair, 0 lone pairs
Cl₂ 1, 6
O₂ 2, 4
N₂ 3, 2
CH₄ 4, 0
NH₃ 3, 1
H₂O 2, 2
HCl 1, 3
CCl₄ 4, 12
Ionisation of a polar compound: $H C l + H_{2} O \to H_{3} O^{+} + C l^{-}$
Polar or non-polar: Same atoms or evenly arranged identical bonds: non-polar | Different atoms with an electronegativity difference: polar

H₂	1 bond pair, 0 lone pairs
Cl₂	1, 6
O₂	2, 4
N₂	3, 2
CH₄	4, 0
NH₃	3, 1
H₂O	2, 2
HCl	1, 3
CCl₄	4, 12

How to solve Covalent Bonding, Polar and Non-polar Molecules questions

For any covalent molecule, count electrons before you draw.

1Write the outer electrons of each atom (H 1, C 4, N 5, O 6, Cl 7).
2Decide how many electrons each atom still needs for a duplet (H) or an octet (others); that is the number of shared pairs it needs.
3Join the atoms with that many shared pairs, and add lone pairs to complete octets.
4Check: bond pairs x 2 + lone pair electrons = total outer electrons of all atoms.
5For polarity, compare electronegativity: identical atoms or a symmetrical molecule is non-polar; otherwise mark the more electronegative atom with delta minus.

Covalent Bonding, Polar and Non-polar Molecules in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Why oil and water do not mix, and why sugar does not light a bulb

Suppose a cook pours cooking oil (a non-polar covalent substance) into water (a polar covalent substance) and the oil floats in a separate layer. She also tests a sugar solution in a battery-and-bulb circuit and finds that the bulb stays off.

Use the idea of polar and non-polar molecules to explain both observations.

Try it first, then show the solutionSolution

Water molecules are polar and attract one another strongly; non-polar oil molecules cannot join in, so they stay as a separate layer.
Sugar dissolves as neutral molecules and produces no ions, so the solution has no charge carriers and does not conduct.

Answer: Non-polar oil does not mix with polar water; a covalent solute like sugar gives no ions, so no current.

Memory hook: Like dissolves like; molecules do not carry current.

Tricks to remember Covalent Bonding, Polar and Non-polar Molecules

Short memory aids. Say each one aloud once, then use it on a question the same day.

Share, do not give
Covalent = Co-operate (share). Electrovalent = Electrons go away (transfer).
Use it when: Telling the two bond types apart.
Lone pair count 0-1-2-3
CH₄ has 0 lone pairs on the central atom, NH₃ has 1, H₂O has 2 and HCl has 3 on Cl: the lone pairs rise as the central atom moves from C to N to O to Cl.
Use it when: Drawing the central atom correctly.
N₂ is the triple
N has 5 electrons and needs 3: nitrogen is a triple bond. O needs 2: double. Cl and H need 1: single.
Use it when: Choosing the number of bonds.

Covalent Bonding, Polar and Non-polar Molecules: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Definition · 1 mark · Very short answerBoard level

Define a covalent bond and name the type of atoms that form it.

Try it first, then show the solutionSolution

A covalent bond is formed by the sharing of electron pairs between two atoms.
It is formed between non-metal atoms.

Answer: A bond formed by sharing pairs of electrons, usually between non-metal atoms.

Example 2: Oxygen and nitrogen molecules · 2 marks · Short answerBoard level

State the number of shared pairs and lone pairs on each atom in (a) an oxygen molecule (O = 8) and (b) a nitrogen molecule (N = 7).

Try it first, then show the solutionSolution

(a) O is 2,6 and needs 2 more electrons: two shared pairs (O=O); the remaining 6 - 2 = 4 electrons on each atom form 2 lone pairs.
(b) N is 2,5 and needs 3 more: three shared pairs (N $\equiv$ N); the remaining 5 - 3 = 2 electrons form 1 lone pair on each atom.

Answer: (a) 2 shared pairs, 2 lone pairs on each O. (b) 3 shared pairs, 1 lone pair on each N.

Example 3: Ammonia and water compared · 4 marks · Long answerHarder board level

Draw electron dot diagrams for ammonia and water. State the number of bond pairs and lone pairs on the central atom of each, and say why both are polar covalent.

Try it first, then show the solutionSolution

NH₃: N (2,5) shares three pairs with three H atoms; 3 bond pairs and 1 lone pair on N.
H₂O: O (2,6) shares two pairs with two H atoms; 2 bond pairs and 2 lone pairs on O.
In both, nitrogen or oxygen is more electronegative than hydrogen and pulls the shared pairs closer, so the bonds are polar.

Answer: NH₃: 3 bond pairs, 1 lone pair. H₂O: 2 bond pairs, 2 lone pairs. Both are polar because N and O are more electronegative than H.

Example 4: Electron count check for CCl₄ · 3 marks · Short answerHarder board level

Carbon tetrachloride has 1 carbon atom (4 outer electrons) and 4 chlorine atoms (7 outer electrons each). Find (a) the total outer electrons, (b) the number of bond pairs, (c) the number of lone pairs in the molecule.

Try it first, then show the solutionSolution

(a) Total outer electrons = 4 + 4 x 7 = 32.
(b) Four single bonds = 4 bond pairs = 8 electrons.
(c) Remaining electrons = 32 - 8 = 24, which is 12 lone pairs (3 on each Cl).

Answer: (a) 32 (b) 4 (c) 12.

Example 5: Identify from properties · 4 marks · Long answerHOTS / competency

Compound X is a liquid at room temperature that does not conduct electricity, dissolves in benzene, and does not dissolve in water. Compound Y is a gas that does not conduct as a gas but gives a conducting solution in water. Name a likely example of each, with reasons.

Try it first, then show the solutionSolution

X is a non-polar covalent compound such as carbon tetrachloride: no ions, weak forces so liquid, soluble in an organic solvent.
Y is a polar covalent compound such as hydrogen chloride: molecules in the gas conduct no current, but in water it ionises to H₃O⁺ and Cl⁻, which carry current.

Answer: X: carbon tetrachloride (non-polar). Y: hydrogen chloride (polar, ionises in water).

Where students lose marks in Covalent Bonding, Polar and Non-polar Molecules

The slips examiners see most often, and what to write instead.

Mistake: Drawing a triple bond for oxygen or a double bond for nitrogen
The number of shared pairs does not match the electrons still needed for an octet.
Wrong working
O at the centre with three shared pairs.
Right working
O needs 2 electrons, so O=O; N needs 3, so N $\equiv$ N.
Do this: Count (8 - outer electrons) for each atom.
Usually costs: 1 mark.
Mistake: Leaving out lone pairs
In NH₃, H₂O and HCl the lone pairs on the central atom are essential; candidates draw only the bond pairs.
Do this: Show every lone pair; NH₃ has 1, H₂O has 2, HCl has 3 on Cl.
Usually costs: 1 mark.
Mistake: Calling all covalent compounds non-conductors
Polar compounds such as HCl form ions in water and conduct.
Do this: Write: pure covalent compounds do not conduct, but polar ones ionise in water.
Usually costs: 1 mark.
Mistake: Calling HCl or NH₃ non-polar
The unequal electronegativity of the two atoms is overlooked.
Do this: Name the more electronegative atom and mark delta minus on it.
Usually costs: 1 mark.

Exam tips

Always write the electron arrangement of each atom first; it justifies the number of shared pairs.
Do not forget lone pairs: marking schemes check them in NH₃, H₂O and HCl.
For "state the difference" items, give one point per property in matching pairs (state, melting point, conduction).
Link polarity to electronegativity in one sentence: the more electronegative atom attracts the shared pair.

Practice questions on Covalent Bonding, Polar and Non-polar Molecules

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
The compound with a triple covalent bond is:
(a) oxygen
(b) chlorine
(c) nitrogen
(d) methane
Hint
N needs three more electrons.
Answer
(c) nitrogen.
Q2 · 1 mark · MCQBoard level
Which of these is a polar covalent compound?
(a) CCl₄
(b) CH₄
(c) Cl₂
(d) HCl
Hint
Different atoms with different electronegativity.
Answer
(d) HCl.
Q3 · 2 marks · Short answerBoard level
Draw the electron dot structure of hydrogen chloride (H = 1, Cl = 17). Mark the bond pair, the lone pairs and the partial charges.
Hint
Cl is 2,8,7.
Answer
One shared pair between H and Cl; three lone pairs on Cl; chlorine, being more electronegative, carries delta minus and hydrogen delta plus.
Q4 · 3 marks · Short answerHarder board level
Give three differences between an electrovalent and a covalent compound.
Hint
Think of state, melting point and conduction.
Answer
Electrovalent: formed by transfer of electrons, hard crystalline solids with high melting point, conduct when molten or in solution. Covalent: formed by sharing, usually gases or liquids or soft solids with low melting point, non-conductors.
Q5 · 3 marks · Short answerHarder board level
Explain why hydrogen chloride is a poor conductor as a gas but its aqueous solution conducts electricity. Write the equation.
Hint
Polar molecules react with water.
Answer
HCl gas has neutral molecules with no free ions. In water it ionises: $H C l + H_{2} O \to H_{3} O^{+} + C l^{-}$ , and the mobile ions carry current.
Q6 · 1 mark · Assertion-reasonHOTS / competency
Assertion (A): Carbon tetrachloride is a non-polar covalent compound although the C-Cl bond is polar.
Reason (R): The four bonds are identical and arranged evenly so that their polarities cancel.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
The chlorine atoms are around carbon symmetrically.
Answer
(a).
Q7 · 3 marks · Short answerHarder board level
Using oxygen (atomic number 8) as an example, explain what a double bond is, how many lone pairs each oxygen atom keeps, and why oxygen is non-polar.
Hint
O is 2,6.
Answer
Two electron pairs are shared between the two O atoms (O=O). Each O has 6 - 2 = 4 non-bonding electrons, i.e. 2 lone pairs. Both atoms are identical, so the shared pairs are equally attracted and the molecule is non-polar.
Q8 · 4 marks · Long answerHarder board level
An element Z has atomic number 17. (a) Write its electron arrangement. (b) Show the formation of its molecule Z2 by electron dot diagram. (c) State why Z2 does not conduct electricity. (d) Name the type of bond.
Hint
Z is chlorine.
Answer
(a) 2,8,7. (b) Each atom shares one electron: one bond pair, three lone pairs on each atom. (c) No ions or free electrons. (d) Single non-polar covalent bond.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.How many shared pairs are there in N₂?Show answer
Three (triple bond).
2.Lone pairs on the nitrogen atom of NH₃?Show answer
One.
3.Name two non-polar covalent compounds with carbon.Show answer
Methane and carbon tetrachloride.
4.Why are covalent compounds low melting?Show answer
The forces between molecules are weak.
5.What is electronegativity?Show answer
The tendency of an atom to attract the shared pair of electrons.

Covalent Bonding, Polar and Non-polar Molecules: frequently asked questions

What is the difference between polar and non-polar covalent compounds?

In polar compounds the shared pair lies nearer to the more electronegative atom, giving partial charges. In non-polar compounds it is shared equally or the bond polarities cancel.

Why does carbon tetrachloride not dissolve in water?

It is non-polar, while water is a polar solvent.

Does water have a lone pair?

Yes, the oxygen atom of a water molecule has two lone pairs; this is used in coordinate bonding.

Why do covalent compounds not conduct electricity?

They contain neutral molecules, with no free ions or electrons to carry charge.