ScienceCBSE Class 10 · Carbon and its Compounds

Covalent Bonding in Carbon and Electron Dot Structures

Updated 14 October 2026 · Fact-checked

A covalent bond forms when two atoms share a pair of electrons so that both reach a noble gas configuration. Carbon, with four valence electrons, cannot easily gain or lose four electrons, so it shares them. Covalent compounds have strong bonds within molecules but weak forces between molecules, so they have low melting and boiling points and conduct poorly.

Understand Covalent Bonding in Carbon

Why carbon shares. Carbon has atomic number 6, so its electrons are arranged 2, 4: four valence electrons. To reach a noble gas configuration it would need to gain or lose four electrons, and both are hard.

Gaining four would make $C^{4 -}$ , but a nucleus with only six protons would struggle to hold ten electrons.
Losing four would make $C^{4 +}$ , but removing four electrons needs a very large amount of energy, leaving six protons holding just two electrons.

So carbon shares its valence electrons with other carbon atoms or with atoms of other elements. A shared pair counts towards the outer shell of both atoms, so both reach a stable configuration. A bond made by sharing a pair of electrons is a covalent bond. Carbon's valency is four (it is tetravalent).

Single, double and triple bonds. One shared pair is a single bond, drawn as one line.

**Hydrogen, $H_{2}$ :** each H has one electron and needs one more to match helium; the two atoms share one pair: H–H.
**Chlorine, $C l_{2}$ ** (2, 8, 7): each needs one electron, so they share one pair: a single bond.
**Oxygen, $O_{2}$ (2, 6): each needs two, so each contributes two electrons, giving two shared pairs: a double bond**, O=O.
**Nitrogen, $N_{2}$ (2, 5): each needs three, so three shared pairs: a triple bond**, N≡N.
**Methane, $C H_{4}$ :** carbon shares one pair with each of four hydrogen atoms: four single bonds. Methane is used as a fuel and is a major component of biogas and CNG.
**Water, $H_{2} O$ and ammonia, $N H_{3}$ :** oxygen forms two single bonds and nitrogen three, with the rest of their outer electrons as unshared pairs.
**Carbon dioxide, $C O_{2}$ :** carbon forms a double bond with each oxygen, O=C=O, sharing all four of its valence electrons.

Electron dot structures. Draw only the valence electrons, as dots for one atom and crosses for the other. Put shared pairs between the two atoms. Then check that every atom except hydrogen has eight electrons around it, and hydrogen has two.

Properties of covalent compounds. Within a molecule the covalent bonds are strong, but the forces between separate molecules are weak. Little energy is needed to pull molecules apart, so melting and boiling points are low: NCERT lists methane melting at 90 K and boiling at 111 K, ethanol at 156 K and 351 K, chloroform at 209 K and 334 K, and acetic acid at 290 K and 391 K. These are far below ionic compounds such as sodium chloride (melting point 1074 K). And because electrons are shared and no charged particles (ions) form, covalent compounds are generally poor conductors of electricity.

In the board exam you will draw dot structures (often of $C H_{4}$ , $O_{2}$ , $N_{2}$ , $C O_{2}$ , ethane or ethene), explain why carbon forms covalent bonds, and compare covalent with ionic compounds.

Covalent Bonding in Carbon: formulas and key facts

Configuration of carbon: $C (Z = 6) : 2, 4$; Four valence electrons; valency four.
Bond types by shared pairs: $1 pair = single; 2 pairs = double; 3 pairs = triple$; $H_{2}$ , $C l_{2}$ single; $O_{2}$ double; $N_{2}$ triple.
Shared pairs from atoms needed: $electrons needed for octet = 8 - valence electrons$; O needs 2 (double bond in $O_{2}$ ), N needs 3 (triple bond in $N_{2}$ ); H needs 1 to reach 2.
Melting and boiling points (NCERT Table 4.1): $C H_{4} : 90 K, 111 K; C_{2} H_{5} O H : 156 K, 351 K; C H_{3} C O O H : 290 K, 391 K$; Low, because intermolecular forces are weak.

How to solve Covalent Bonding in Carbon questions

To draw any electron dot structure in this chapter, follow these steps.

1Write the electronic configuration of each atom and count its valence electrons.
2Find how many electrons each atom needs: 8 minus valence electrons (2 minus 1 for hydrogen).
3Join the atoms with a skeleton: carbon in the middle with four bonds, hydrogen always at the end with one bond.
4Put one shared pair (one dot and one cross) between each bonded pair of atoms; add extra pairs (double or triple bond) where an atom still needs electrons.
5Place the remaining valence electrons as unshared pairs on the atoms.
6Check: each atom other than hydrogen has 8 electrons around it; each hydrogen has 2; total electrons drawn = total valence electrons.

Covalent Bonding in Carbon 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.

Properties of covalent compounds

Suppose you are cooking on a CNG stove, and you notice that the fuel is a gas at room temperature while table salt on the shelf is a hard solid. Your cousin asks why the gas is not also a solid like salt.

Explain the difference using the type of bonding in methane and in sodium chloride, and say whether methane would conduct electricity.

Try it first, then show the solutionSolution

CNG is mainly methane, $C H_{4}$ , a covalent compound: carbon shares one electron pair with each of four hydrogen atoms.
The bonds inside each methane molecule are strong, but the forces between separate molecules are weak, so very little energy pulls them apart. Methane boils at 111 K, far below room temperature (about 300 K), so it is a gas.
Sodium chloride is ionic: strong attraction between $N a^{+}$ and $C l^{-}$ ions throughout the solid gives it a high melting point (1074 K).
Methane has no ions or free charged particles, so it does not conduct electricity.

Answer: Methane's molecules are held by weak intermolecular forces, so it boils at 111 K and is a gas; salt is held by strong ionic attraction and is solid. Methane does not conduct, having no ions.

Memory hook: Strong inside, weak outside: covalent molecules part easily, so they melt and boil low.

Tricks to remember Covalent Bonding in Carbon

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

Carbon can't take or give four
Gain 4: nucleus too weak (6 protons, 10 electrons). Lose 4: too much energy. So share.
Use it when: 'Why does carbon form covalent bonds?' answers.
H–O–N–C bond counts
H makes 1 bond, O makes 2, N makes 3, C makes 4 (HONC 1-2-3-4).
Use it when: Building skeletons and checking dot structures.
Strong in, weak between
Covalent: strong bonds in a molecule, weak forces between molecules.
Use it when: Explaining low melting and boiling points.

Covalent Bonding in Carbon: solved examples

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

Example 1: Why carbon shares electrons · 2 marks · Very short answerBoard level

Carbon neither forms $C^{4 +}$ nor $C^{4 -}$ ions. Explain why, and state how carbon attains a noble gas configuration.

Try it first, then show the solutionSolution

$C^{4 -}$ : a nucleus with six protons cannot hold ten electrons easily; $C^{4 +}$ : removing four electrons needs a very large amount of energy (1 mark).
Carbon shares its four valence electrons with other atoms, forming covalent bonds; the shared electrons count towards both atoms' outer shells (1 mark).

Answer: Gaining or losing four electrons is too difficult; carbon shares its four valence electrons instead.

Example 2: Dot structures of two diatomic gases · 3 marks · Short answerHarder board level

Draw the electron dot structures of oxygen ( $O_{2}$ ) and nitrogen ( $N_{2}$ ). State the type of bond in each and explain why it forms. (Atomic numbers: O = 8, N = 7)

Try it first, then show the solutionSolution

O is 2, 6: six valence electrons, needs two. Each O contributes two electrons, giving two shared pairs between the atoms; each O keeps two unshared pairs. Double bond, O=O (1½ marks).
N is 2, 5: five valence electrons, needs three. Each N contributes three electrons, giving three shared pairs; each N keeps one unshared pair. Triple bond, N≡N (1½ marks).

Answer: $O_{2}$ : two shared pairs, double bond. $N_{2}$ : three shared pairs, triple bond. Each atom completes its octet.

Example 3: Carbon dioxide · 3 marks · Short answerHarder board level

Draw the electron dot structure of carbon dioxide ( $C O_{2}$ ). How many shared pairs and how many unshared (lone) pairs does the molecule have in total? Is $C O_{2}$ likely to conduct electricity? Give a reason.

Try it first, then show the solutionSolution

C (2, 4) shares two electrons with each O (2, 6); each O shares two of its own with C. That gives a double bond on each side: O=C=O (1 mark).
Shared pairs: 2 + 2 = 4. Each O has 6 − 2 = 4 unshared electrons = 2 lone pairs, so 4 lone pairs in total. Check octets: C has 4 pairs = 8; each O has 2 shared + 2 lone pairs = 8 (1 mark).
No: electrons are shared, no ions form, so covalent $C O_{2}$ does not conduct (1 mark).

Answer: O=C=O with 4 shared pairs and 4 lone pairs; no conduction because there are no ions.

Example 4: Ethane versus ethene · 5 marks · Long answerHarder board level

(a) Draw the structures of ethane ( $C_{2} H_{6}$ ) and ethene ( $C_{2} H_{4}$ ) and show how the valency of each carbon is satisfied. (b) Draw the electron dot structure of ethyne ( $C_{2} H_{2}$ ) and state the number of shared pairs between the carbon atoms. (c) Which of the three would you expect to be most reactive, and why?

Try it first, then show the solutionSolution

(a) Ethane: C–C single bond; each C bonds to three H, so each C has 1 + 3 = 4 bonds (1 mark).
(a) Ethene: after a C–C single bond and two H on each C, one valency per carbon is left; it is satisfied by making the carbon-carbon bond double: $H_{2} C = C H_{2}$ (1½ marks).
(b) Ethyne: each C has one H; the remaining three valencies of each C form a triple bond, so three shared pairs between the carbons: H–C≡C–H (1½ marks).
(c) Ethene and ethyne are unsaturated (double or triple bonds) and are more reactive than saturated ethane (1 mark).

Answer: (a) Ethane single C–C; ethene double C=C. (b) Ethyne has three shared pairs (triple bond). (c) The unsaturated ones (ethene, ethyne) are more reactive than ethane.

Example 5: Comparing two compounds · 3 marks · Short answerHOTS / competency

Compound P melts at 90 K, does not conduct electricity in any state, and is a gas at room temperature. Compound Q melts at 1074 K and conducts when molten. (a) Identify the type of bonding in each. (b) Explain how the bonding accounts for the melting points. (c) A student says 'P has weak bonds'. Correct the statement.

Try it first, then show the solutionSolution

(a) P: covalent (no ions, low melting point; it matches methane). Q: ionic (conducts when molten, high melting point; it matches NaCl) (1 mark).
(b) Q: strong attraction between ions needs much energy to overcome. P: weak forces between molecules need little energy (1 mark).
(c) The covalent bonds within P's molecules are strong; it is the forces between the molecules that are weak (1 mark).

Answer: (a) P covalent, Q ionic. (b) Weak intermolecular forces vs strong inter-ionic attraction. (c) Bonds inside P are strong; only intermolecular forces are weak.

Where students lose marks in Covalent Bonding in Carbon

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

Mistake: Showing all electrons instead of valence electrons
Students draw the full 2, 8, 7 for chlorine.
Wrong working
Seventeen dots around each Cl in $C l_{2}$ .
Right working
Seven valence dots around each Cl, with one shared pair between them.
Do this: Only valence-shell electrons are drawn.
Usually costs: ½ to 1 mark per structure.
Mistake: Wrong bond in $O_{2}$ or $N_{2}$
Students draw a single bond for all diatomic gases.
Wrong working
O–O with one shared pair.
Right working
O=O with two shared pairs; N≡N with three.
Do this: Count electrons needed: O needs 2 (double), N needs 3 (triple).
Usually costs: 1 mark.
Mistake: Saying covalent compounds have weak bonds
Low melting points are linked to the wrong force.
Wrong working
Methane melts at a low temperature because C–H bonds are weak.
Right working
C–H bonds are strong; the forces between methane molecules are weak.
Do this: Distinguish 'bonds within' from 'forces between' molecules.
Usually costs: 1 mark in reasoning questions.
Mistake: Octet not checked
Students stop before counting electrons around each atom.
Wrong working
$C O_{2}$ drawn with single C–O bonds, leaving carbon with 6 electrons.
Right working
O=C=O, so carbon has 8 electrons around it.
Do this: Count electrons around every atom as the last step.
Usually costs: 1 mark.

Exam tips

Use dots for one atom and crosses for the other; it makes shared pairs obvious to the examiner.
Circle or box the shared pairs and label 'single', 'double' or 'triple bond' if asked.
When explaining properties, use the two ideas: weak intermolecular forces (low melting points) and no ions (poor conduction).
Learn the configurations: H 1, C 2,4, N 2,5, O 2,6, S 2,8,6, Cl 2,8,7.
Allotropes of carbon appear in a 'More to Know' box, which is not assessed in the board exam; focus on bonding.

Practice questions on Covalent Bonding in Carbon

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 number of shared electron pairs in a molecule of nitrogen is:
(a) 1 (b) 2 (c) 3 (d) 4
Hint
Nitrogen needs three electrons to complete its octet.
Answer
(c) 3, a triple bond.
Q2 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Covalent compounds are generally poor conductors of electricity.
Reason (R): Covalent compounds have strong forces of attraction between their molecules.
(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
Why don't they conduct, and are intermolecular forces strong?
Answer
(c). A is true because no ions form when electrons are shared; R is false because the intermolecular forces are weak.
Q3 · 2 marks · Very short answerBoard level
Draw the electron dot structures of (a) methane and (b) ammonia. For each, state the number of single bonds and the number of lone pairs on the central atom.
Hint
C has 4 valence electrons; N has 5.
Answer
(a) $C H_{4}$ : C shares one pair with each of four H; 4 single bonds, 0 lone pairs. (b) $N H_{3}$ : N shares one pair with each of three H; 3 single bonds, 1 lone pair on N.
Q4 · 3 marks · Short answerHOTS / competency
Draw the electron dot structure of water. Then explain why water, a covalent compound, has a much higher boiling point (373 K) than methane (111 K), using only ideas from this topic, and say why the comparison with sodium chloride is still valid.
Hint
Boiling depends on forces between molecules.
Answer
O shares one pair with each H; O has two lone pairs (8 electrons around O, 2 around each H). Boiling separates molecules, so it depends on the forces between molecules; water's must be stronger than methane's, though both are much weaker than the attraction between ions in NaCl (which boils at 1686 K). So covalent compounds still boil far lower than ionic ones.
Q5 · 4 marks · Case-basedHOTS / competency
Read the passage and answer.
Suppose a student builds models of molecules using balls for atoms and sticks for shared pairs. For a molecule of sulphur she needs eight sulphur balls joined in a ring. Sulphur has atomic number 16.
(a) How many valence electrons does a sulphur atom have? (1 mark)
(b) In the ring, each S atom is bonded to two neighbours by single bonds. How many sticks (shared pairs) are needed for the whole $S_{8}$ molecule? (1 mark)
(c) Show that each S atom completes its octet and find the total number of lone pairs in $S_{8}$ . (2 marks)
Hint
A ring of 8 atoms has 8 links.
Answer
(a) 2, 8, 6: six valence electrons. (b) 8 single bonds in a ring of 8 atoms, so 8 sticks. (c) Each S shares 2 pairs (4 electrons) and keeps 6 − 2 = 4 electrons as 2 lone pairs; 4 + 4 = 8, an octet. Total lone pairs = 8 × 2 = 16.
Q6 · 3 marks · Short answerHarder board level
Chlorine (Z = 17) forms $C l_{2}$ and also forms $C C l_{4}$ with carbon. (a) Draw the electron dot structure of $C l_{2}$ . (b) Predict the structure of $C C l_{4}$ by analogy with methane and state the number of shared pairs. (c) Would you expect $C C l_{4}$ to have a high or low boiling point compared with sodium chloride? Why?
Hint
Each Cl needs one electron, just like each H in methane.
Answer
(a) Each Cl (2, 8, 7) shares one electron: one shared pair, and each Cl has three lone pairs. (b) Like methane, carbon shares one pair with each of four Cl atoms: 4 shared pairs (each Cl also has 3 lone pairs). (c) Low; it is covalent with weak forces between molecules, while NaCl has strong ionic attraction.

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.What is a covalent bond?Show answer
A bond formed by sharing a pair of electrons between two atoms.
2.Why is carbon tetravalent?Show answer
It has four valence electrons.
3.Bond in $O_{2}$ ?Show answer
Double bond (two shared pairs).
4.Bond in $N_{2}$ ?Show answer
Triple bond (three shared pairs).
5.Why are covalent compounds poor conductors?Show answer
Electrons are shared and no ions are formed.
6.Boiling point of methane in NCERT Table 4.1?Show answer
111 K.

Covalent Bonding in Carbon: frequently asked questions

Why does carbon form covalent bonds and not ionic bonds?

Carbon would need to gain or lose four electrons. Holding ten electrons with six protons is difficult, and removing four electrons needs too much energy, so carbon shares its electrons.

What is the difference between single, double and triple covalent bonds?

A single bond is one shared pair, a double bond two shared pairs and a triple bond three shared pairs of electrons between two atoms.

Why do covalent compounds have low melting and boiling points?

The bonds inside molecules are strong, but the forces between molecules are weak, so little energy is needed to separate molecules.

How do I draw the electron dot structure of methane?

Put C in the centre with four valence electrons and four H atoms around it, each sharing one pair with carbon. Carbon then has eight electrons and each hydrogen has two.

Are allotropes of carbon (diamond, graphite, fullerene) asked in the board exam?

They are in a 'More to Know' box in NCERT. CBSE does not assess information in boxes in the year-end exam.