Who this is for: Cambridge IGCSE Chemistry (0620) students who can draw a water molecule but confuse covalent bonds with intermolecular forces — or lose marks explaining why simple molecular substances have low melting points.
What query it owns: how to understand and revise simple molecules and covalent bonds in Cambridge IGCSE Chemistry.
Why this is safe: this page owns the covalent-bonding revision-guide angle in the cambridge-igcse-chemistry folder, while Tutopiya’s Simple Molecules and Covalent Bonds subtopic page owns the learning resource and the free Covalent Bonds quiz owns the practice.

A covalent bond forms when two non-metal atoms share a pair of electrons. Simple molecular substances consist of small molecules held together by weak intermolecular forces between molecules — not to be confused with the strong covalent bonds within each molecule. Cambridge IGCSE Chemistry (0620) tests dot-and-cross diagrams, bond counts, and property explanations.

Key takeaways

• Covalent bond = shared pair of electrons between non-metal atoms.
• Simple molecular substances have low melting/boiling points — weak intermolecular forces break on heating, not covalent bonds.
• Single, double and triple bonds involve 1, 2 or 3 shared pairs respectively.
• Non-metal + non-metal → usually covalent; draw outer-shell electrons only.
• Confirm with the Simple Molecules and Covalent Bonds quiz.

What are simple molecules and covalent bonds?

Covalent bonding occurs when atoms of non-metals share electrons to achieve stable outer-shell arrangements. Simple molecular substances such as water, carbon dioxide and methane exist as discrete molecules with strong covalent bonds inside each molecule and weak forces between molecules.

Full notes are on Tutopiya’s Simple Molecules and Covalent Bonds subtopic page.

Bond types — summary table

Molecule	Bond type	Shared pairs	Example formula
Hydrogen	Single	1	H₂
Water	Single	2 (O–H × 2)	H₂O
Oxygen	Double	2	O₂
Nitrogen	Triple	3	N₂
Methane	Single	4 (C–H × 4)	CH₄

Covalent vs ionic vs intermolecular — comparison table

Feature	Covalent bond (within molecule)	Intermolecular force (between molecules)	Ionic bond
Strength	Strong	Weak	Strong
Between	Atoms in same molecule	Separate molecules	Ions in lattice
Breaks when	Very high temperature / chemical reaction	Low melting/boiling	High melting point

How to answer covalent bonding questions — step by step

1. Count valence electrons for each non-metal atom.
2. Share pairs to give each atom a full outer shell (except hydrogen — 2 electrons).
3. Draw dot-and-cross — shared pairs in overlap region.
4. For property questions, state low melting point is due to weak intermolecular forces, not weak covalent bonds.
5. Test with the free Covalent Bonds quiz.

Past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical stem
Draw	Dot-and-cross diagram	”Draw a dot-and-cross diagram for a methane molecule.”
Explain	Property linked to structure	”Explain why chlorine is a gas at room temperature.”
State	Short fact	”State the type of bond in an oxygen molecule.”
Describe	How bonding works	”Describe covalent bonding in a hydrogen molecule.”

Worked exam-style stems (how to answer the wording)

1. “Draw a dot-and-cross diagram for a water molecule.” O shares 1 pair with each H; O has 2 lone pairs; each H has 2 electrons. Draw = correct shared and lone pairs.
2. “Explain why iodine has a low melting point.” Iodine is a simple molecular substance; weak intermolecular forces between I₂ molecules require little energy to overcome. Not “weak covalent bonds”.
3. “State how many covalent bonds are in one molecule of nitrogen.” One triple bond (or three shared pairs). State = concise.

Practise more on the Atoms topical past paper questions.

How covalent bonding connects to giant structures

Simple molecules contrast with Giant Covalent Structures (diamond, graphite, silicon dioxide) where covalent bonds extend through the whole structure. Compare properties: giant covalent = very high melting points; simple molecular = low. The Cambridge IGCSE Chemistry hub links both.

Common mistakes students make

• Saying covalent bonds break when ice melts — intermolecular forces break; H₂O molecules stay intact.
• Drawing ionic transfer for covalent molecules.
• Forgetting lone pairs on oxygen and nitrogen in diagrams.
• Confusing double bond (2 shared pairs) with two separate single bonds.
• Skipping the Covalent Bonds quiz.

When you need more support

If explain questions on melting points keep failing, compare simple molecular with giant covalent on the Giant Covalent Structures subtopic, then book a Cambridge IGCSE Chemistry tutor.

Frequently asked questions

What is the difference between a covalent bond and an intermolecular force? A covalent bond holds atoms together inside a molecule; intermolecular forces act between separate molecules.

Why do simple molecular substances not conduct electricity? They have no free-moving charged particles (ions or delocalised electrons).

How many bonds does carbon form in methane? Four single covalent bonds to four hydrogen atoms.

How do I revise covalent bonding effectively? Read subtopic notes, practise draw/explain stems, take the Covalent Bonds quiz, then study giant covalent structures for contrast.

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