What are simple molecules in the context of Cambridge IGCSE Chemistry?

In Cambridge IGCSE Chemistry, simple molecules refer to small groups of atoms bonded together by covalent bonds. These molecules typically consist of a few atoms, such as H2O (water), CO2 (carbon dioxide), and O2 (oxygen). They are characterized by strong covalent bonds within the molecule but weak intermolecular forces between molecules, leading to low melting and boiling points.

How do covalent bonds form between atoms?

Covalent bonds form when two atoms share one or more pairs of electrons to achieve a full outer shell, resembling the electron configuration of noble gases. This sharing of electrons allows each atom to attain stability. For example, in a water molecule (H2O), each hydrogen atom shares an electron with the oxygen atom, resulting in a stable covalent bond.

What is the difference between covalent bonds and ionic bonds?

Covalent bonds involve the sharing of electron pairs between atoms, typically between non-metal elements, resulting in the formation of simple molecules. In contrast, ionic bonds occur when electrons are transferred from one atom to another, usually between metal and non-metal elements, creating ions that attract each other due to opposite charges. This difference in bonding leads to distinct properties in the resulting compounds.

Why do simple molecules have low melting and boiling points?

Simple molecules have low melting and boiling points because they are held together by weak intermolecular forces, such as van der Waals forces or hydrogen bonds. These forces are much weaker than the covalent bonds within the molecules, requiring less energy to overcome. As a result, simple molecular substances are often gases or liquids at room temperature.

Can you explain the concept of a double covalent bond with an example?

A double covalent bond occurs when two pairs of electrons are shared between two atoms. This type of bond is stronger and shorter than a single covalent bond. An example is the oxygen molecule (O2), where each oxygen atom shares two electrons with the other, forming a double bond. This sharing allows both oxygen atoms to achieve a stable electron configuration.

Why is "Saying simple molecular substances have low melting points because they have weak covalent bonds." a common mistake in Simple Molecules and Covalent Bonds?

Why it happens: Confusing the covalent bonds INSIDE molecules with the forces BETWEEN molecules. How to avoid it: Covalent bonds are STRONG. The low melting/boiling point is due to WEAK INTERMOLECULAR FORCES between molecules being overcome — the covalent bonds inside the molecules are NOT broken. Source: 0620/42 — recurring

Why is "Saying simple molecular substances conduct electricity when molten." a common mistake in Simple Molecules and Covalent Bonds?

Why it happens: Generalising from ionic compounds, which conduct when molten. How to avoid it: Simple molecular substances have NO free electrons and NO ions, so they do not conduct in any state.

Why is "Drawing electrons being transferred (gained/lost) in a covalent bond." a common mistake in Simple Molecules and Covalent Bonds?

Why it happens: Mixing covalent bonding up with ionic bonding. How to avoid it: Covalent bonding is SHARING a pair of electrons that sits between the two atoms — nothing is transferred.

Why is "Drawing 8 electrons around a hydrogen atom." a common mistake in Simple Molecules and Covalent Bonds?

Why it happens: Over-applying the octet rule. How to avoid it: Hydrogen is stable with just 2 outer electrons (helium configuration), so it forms only one single bond.

Cambridge IGCSE Chemistry (0620)

Simple Molecules and Covalent Bonds

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Short Notes - Simple Molecules and Covalent Bonds

Detailed Study Notes

Detailed notes on Atoms, Elements and Compounds for Cambridge IGCSE Chemistry, covering key concepts, explanations, examples, and exam-focused revision points.

Simple Molecules and Covalent Bonds — Cambridge IGCSE 0620 Chemistry Extended (2026)

Atoms sharing electrons, with weak intermolecular forces between molecules. Why simple molecular substances have low melting points and don't conduct.

At a glance

Covalent bond: shared pair of electrons between two non-metal atoms.
Each atom contributes one electron to a single bond.
Multiple bonds: 2 shared pairs (double, e.g. O=O), 3 shared pairs (triple, e.g. N≡N).
Simple molecular substances: small discrete molecules with weak forces BETWEEN molecules.
Properties: low m.p./b.p., often gases or liquids, don't conduct (no charged particles).
Examples: H₂, O₂, N₂, H₂O, CO₂, CH₄, HCl.

What you’ll learn

Mapped to the Cambridge IGCSE 0620 syllabus (2026-2028).

2.2 — Describe the formation of covalent bonds by sharing of electron pairs.
2.2 — Draw dot-and-cross diagrams for simple molecules.
2.2 — Describe the properties of simple molecular substances.

What is a covalent bond?

Two non-metal atoms share a pair of electrons. Each ends up with a noble-gas configuration.

Covalent bond. A SHARED pair of electrons between two non-metal atoms.

Why share? Each atom is closer to a full outer shell (a noble-gas configuration). The shared electrons COUNT for BOTH atoms.

Worked: H₂ (hydrogen molecule).

Each H atom has 1 electron (config: 1).
They share both → each H 'sees' 2 electrons → like helium (full 1st shell).
Forms a single covalent bond H–H.

Each H now counts two electrons in its shell — the helium configuration — by sharing one pair.

Worked: H₂O (water).

O has 6 outer e⁻; needs 2 more for full shell.
Each H shares 1 e⁻ with O.
O ends up with 8 (full); each H ends up with 2 (full).

Multiple bonds.

Single (1 pair shared): H₂, HCl, H₂O.
Double (2 pairs): O=O, CO₂ (each O double bonds to C: O=C=O).
Triple (3 pairs): N≡N (very strong; why N₂ is so unreactive).

Each extra shared pair adds another line to the bond — and makes the bond stronger.

Diagram conventions. Dots and crosses to distinguish electrons from each atom. A bond = a pair (one dot + one cross) between two atoms.

Each bond is one shared pair; O reaches 8 outer electrons and each H reaches 2.

Cambridge tip. Always count BOTH the dots and crosses around an atom; should equal noble-gas configuration (2, 8, 8) when the molecule is correctly drawn.

Covalent bond = shared pair of electrons.
Both atoms 'see' the shared electrons.
Single, double, triple bonds.
Goal: full outer shell for each atom.

Properties of simple molecular substances

Strong covalent bonds INSIDE the molecule; weak forces BETWEEN molecules → low m.p., poor conductivity.

Two types of force in a simple molecular substance.

Within molecules: covalent bonds (strong).
Between molecules: weak intermolecular forces.

When you melt or boil a molecular substance, you only break the WEAK intermolecular forces — the strong covalent bonds INSIDE molecules are NOT broken.

Melting or boiling overcomes the weak forces between molecules, not the strong bonds inside them.

Result: low m.p. and b.p. Often these substances are gases (O₂, N₂, CO₂) or liquids (H₂O, ethanol) at room temperature.

No conductivity. No free electrons; no free ions. Insulators in solid, liquid, and dissolved states.

Solubility. Some are soluble in water (e.g. sugar, ethanol — polar molecules); others are insoluble (e.g. oils, hexane — non-polar).

Property	Simple molecular substance	Reason
Melting / boiling point	Low — often gases (O₂, N₂, CO₂) or liquids (H₂O, ethanol) at room temperature	Only the weak forces between molecules need to be overcome
Electrical conductivity	Does not conduct as a solid, liquid or in solution	No free electrons and no free ions
Solubility in water	Some soluble (sugar, ethanol); others insoluble (oils, hexane)	Polar molecules dissolve in water; non-polar ones do not

Worked qualitative. Why is the b.p. of H₂O ( $100\degree\text{C}$ ) much higher than CH₄ ( $-161\degree\text{C}$ ), even though both are simple molecules? Water has stronger intermolecular forces (specifically, hydrogen bonds). CH₄ has only weak van der Waals forces. The covalent bonds are not what's being broken in either case.

Cambridge wording. When asked "why does CO₂ have a low boiling point?" — say "The covalent bonds within CO₂ molecules are strong, but the FORCES BETWEEN molecules are weak. Only the weak forces need to be overcome to boil." Don't say "the covalent bonds break" — they don't, when you just boil the substance.

Strong covalent bonds INSIDE molecules.
Weak forces BETWEEN molecules.
Boiling breaks intermolecular forces, NOT bonds.
Low m.p. / b.p. → often gas or liquid.
Doesn't conduct: no free charges.

Quick recap

Covalent bond: shared pair of electrons (non-metal atoms).
Single, double, triple = 1, 2, 3 shared pairs.
Inside molecule: STRONG covalent bonds.
Between molecules: WEAK forces.
Low m.p./b.p.; doesn't conduct.
Boiling breaks intermolecular forces, not covalent bonds.

Memorise this

Verbatim phrases and definitions Cambridge mark schemes credit.

Covalent bond — shared pair of electrons between two non-metal atoms.
Simple molecular substance — substance made of small discrete molecules.
Intermolecular force — weak attraction between molecules (compared to a covalent bond).

How it’s examined

Covalent bonding is examined every Paper 2 (4-5 marks: dot-and-cross diagrams, identify bond type) and every Paper 4 (6-8 marks: explain m.p./b.p., draw molecules, multiple bonds). Examiner reports flag two errors: missing electrons in dot-and-cross diagrams (need to total to noble gas), and saying 'covalent bonds break' when a substance simply melts.

Sources: Cambridge IGCSE Chemistry 0620 syllabus 2026-2028 (2.2); 0620/22 May/Jun 2024 — Q5 (covalent dot-and-cross); 0620 Examiner Reports 2022-2024. Last reviewed 2026-05-06.

Take this whole topic with you

Step-by-step worked examples — Simple Molecules and Covalent Bonds

Step-by-step solutions to past-paper-style questions on simple molecules and covalent bonds, written exactly the way a tutor would explain them at the board.

1Define a covalent bond in Cambridge wording
Getting started• definition
Question
Define a covalent bond using the precise Cambridge mark-scheme wording.
Step-by-step solution
1. Step 1
  A covalent bond is a SHARED PAIR of electrons.
2. Step 2
  The sharing occurs between two NON-METAL atoms.
3. Step 3
  Sharing lets each atom reach a noble-gas (full outer-shell) configuration.
Answer
A covalent bond is a shared pair of electrons between two non-metal atoms.
Examiner tip
Two key phrases score: 'shared pair of electrons' AND 'between non-metal atoms'. 'Sharing' alone is not enough — examiners want the word PAIR.
2Dot-and-cross of $\text{H}_{2}$
Getting started• dot and cross, single bond
Question
Describe the dot-and-cross diagram for a hydrogen molecule, $\text{H}_{2}$ .
Step-by-step solution
1. Step 1
  Each hydrogen atom has 1 outer electron and needs 2 (the helium duplet) to be stable.
2. Step 2
  The two atoms share ONE pair of electrons — one dot from one atom and one cross from the other — giving a single covalent bond.
3. Step 3
  Both atoms now have 2 electrons in their (only) shell: a full outer shell.
Answer
Two overlapping circles with a single shared pair (one dot, one cross) in the overlap: $\text{H}\!-\!\text{H}$ .
Examiner tip
Hydrogen needs only 2 outer electrons, NOT 8 — never draw an octet around H.
3Dot-and-cross of $\text{H}_{2}\text{O}$
Building confidence• Adapted from 0620/42 May/Jun 2024 Q5• dot and cross, water, lone pair
Question
Describe the bonding in a water molecule, $\text{H}_{2}\text{O}$ , including any lone pairs.
Step-by-step solution
1. Step 1
  Oxygen has 6 outer electrons; each hydrogen has 1 outer electron.
2. Step 2
  Oxygen shares one pair with each hydrogen → TWO single covalent bonds (two $\text{O}\!-\!\text{H}$ bonds).
3. Step 3
  This uses 2 of oxygen's electrons in bonds, leaving its other 4 outer electrons as TWO lone pairs.
4. Step 4
  Oxygen now has 8 outer electrons (octet) and each hydrogen has 2 (duplet) — all atoms stable.
Answer
$\text{H}\!-\!\text{O}\!-\!\text{H}$ : two shared pairs (one per O–H bond) plus two lone pairs on the oxygen.
Examiner tip
Don't forget the TWO lone pairs on oxygen — they are commonly omitted and lose a mark on a 'complete' diagram.
4Triple bond in $\text{N}_{2}$
Building confidence• triple bond, dot and cross
Question
Explain, using electron numbers, why nitrogen ( $\text{N}_{2}$ ) contains a triple bond.
Step-by-step solution
1. Step 1
  Each nitrogen atom has 5 outer electrons, so each needs 3 more to reach an octet.
2. Step 2
  The two atoms share THREE pairs of electrons (a triple bond) so that both reach 8 outer electrons.
3. Step 3
  Each atom also keeps one lone pair (the 2 outer electrons not used in bonding).
Answer
Three shared pairs: $\text{N}\!\equiv\!\text{N}$ , with one lone pair on each nitrogen atom.
Examiner tip
Count shared pairs carefully: $\text{O}_{2}$ has a double bond (2 pairs), $\text{N}_{2}$ a triple bond (3 pairs).
5Why simple molecular substances have low melting/boiling points
Stretch• properties, intermolecular forces, reasoning
Question
Methane ( $\text{CH}_{4}$ ) melts at $-182\,°\text{C}$ but sodium chloride melts at $801\,°\text{C}$ . Explain this difference fully.
Step-by-step solution
1. Step 1
  Methane is a SIMPLE MOLECULAR substance: it has STRONG covalent bonds INSIDE each molecule but only WEAK intermolecular forces BETWEEN molecules.
2. Step 2
  Melting and boiling only separate the molecules — they break the WEAK intermolecular forces, NOT the strong covalent bonds.
3. Step 3
  Because the intermolecular forces are weak, little energy is needed, so the melting and boiling points are LOW.
4. Step 4
  Sodium chloride is a GIANT IONIC lattice: melting it requires breaking many strong electrostatic forces between oppositely charged ions throughout the lattice, which needs a large amount of energy → very high melting point.
Answer
Methane: melting overcomes only weak intermolecular forces (not the strong covalent bonds inside molecules), so little energy is needed → low m.p. NaCl: a giant ionic lattice with strong electrostatic forces between ions → far more energy needed → high m.p.
Examiner tip
The marks live in the contrast: WEAK intermolecular forces overcome (NOT covalent bonds) for the molecular substance, versus STRONG forces throughout a giant lattice for the ionic one.
6Relating $M_{\text{r}}$ to boiling point
Stretch• Paper 4 (Extended) data-trend style• properties, intermolecular forces, trend
Question
The halogens boil at: $\text{F}_{2}$ $-188\,°\text{C}$ , $\text{Cl}_{2}$ $-34\,°\text{C}$ , $\text{Br}_{2}$ $59\,°\text{C}$ , $\text{I}_{2}$ $184\,°\text{C}$ . Explain this trend in terms of bonding.
Step-by-step solution
1. Step 1
  All four are SIMPLE MOLECULAR substances made of diatomic molecules held to one another by weak intermolecular forces.
2. Step 2
  As you go down the group, the relative molecular mass $M_{\text{r}}$ of the molecules INCREASES ( $\text{F}_{2} = 38$ , $\text{Cl}_{2} = 71$ , $\text{Br}_{2} = 160$ , $\text{I}_{2} = 254$ ).
3. Step 3
  Larger molecules have STRONGER intermolecular forces between them.
4. Step 4
  Stronger intermolecular forces need MORE energy to overcome, so the boiling point rises down the group.
Answer
Boiling point increases because the molecules get larger ( $M_{\text{r}}$ increases) down the group, so the intermolecular forces between them are stronger and need more energy to overcome. The covalent bonds inside the molecules are not broken on boiling.
Examiner tip
Link the size of the molecule ( $M_{\text{r}}$ ) to the STRENGTH of the intermolecular forces, then to the energy needed. Stating 'bigger molecule = higher b.p.' without the forces step loses marks.

Model Answers — Simple Molecules and Covalent Bonds

High-scoring sample answers for simple molecules and covalent bonds on the Cambridge IGCSE 0620 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.

Question 1
Paper 4 short-answer style1 mark
State what is meant by a covalent bond. (1 mark)
Model answer
A covalent bond is a shared pair of electrons (between two non-metal atoms).
Why this scores
One mark for 'shared pair of electrons'. The word PAIR is essential — 'shared electrons' on its own is not enough.
Question 2
Paper 4 structured style2 marks
Hydrogen chloride, $\text{HCl}$ , is a simple molecule. State the number of bonding pairs and the number of lone pairs of electrons in a molecule of $\text{HCl}$ . (2 marks)
Model answer
There is one bonding (shared) pair of electrons forming the single $\text{H}\!-\!\text{Cl}$ covalent bond, and three lone pairs of electrons on the chlorine atom.
Why this scores
One mark for 1 bonding pair; one mark for 3 lone pairs on Cl. Chlorine has 7 outer electrons — 1 is used in the bond, leaving 6 as three lone pairs.
Question 3
Paper 4 structured style3 marks
Describe the bonding in a molecule of carbon dioxide, $\text{CO}_{2}$ . Refer to the type and number of bonds. (3 marks)
Model answer
Carbon has 4 outer electrons and each oxygen has 6. The carbon atom forms a double covalent bond (two shared pairs of electrons) with each oxygen atom, giving the structure $\text{O}\!=\!\text{C}\!=\!\text{O}$ . This means there are two double bonds (four shared pairs in total), and every atom achieves a full outer shell of 8 electrons.
Why this scores
Three marks: (1) double bond / two shared pairs; (2) to each oxygen / two double bonds; (3) all atoms reach a full outer shell (octet). Each O also has two lone pairs.
Question 4
Paper 4 (Extended) structured style4 marks
Simple molecular substances such as iodine do not conduct electricity and are insoluble in water. Explain these two properties. (4 marks)
Model answer
Simple molecular substances do not conduct electricity because they contain no free electrons that are able to move, and no ions — the molecules are neutral. With no mobile charged particles, there is nothing to carry a current in any state. They are often insoluble in water because the weak intermolecular forces between their molecules are similar to, but not as favourable as, the forces between water molecules; water molecules are attracted more strongly to one another than to the non-polar molecules, so the substance does not dissolve.
Why this scores
Four marks: no free electrons; no ions/no mobile charged particles to carry current; and for solubility, reference to weak intermolecular forces / non-polar molecules not interacting favourably with water.
Question 5
Paper 4 (Extended) structured style5 marks
Carbon dioxide is a simple molecular substance with a very low boiling point. Explain, in terms of the forces present, why the boiling point is low. (5 marks)
Model answer
A molecule of carbon dioxide is held together internally by strong covalent bonds (the double bonds between carbon and oxygen). However, between separate $\text{CO}_{2}$ molecules there are only weak intermolecular forces. When carbon dioxide boils, the molecules are separated from one another, so it is only these weak intermolecular forces that are overcome — the strong covalent bonds inside each molecule are NOT broken. Because the intermolecular forces are weak, only a small amount of energy is needed to separate the molecules, so the boiling point is low.
Why this scores
Five marks: strong covalent bonds inside the molecule; weak intermolecular forces between molecules; boiling overcomes the intermolecular forces; covalent bonds are NOT broken; little energy needed → low b.p. The 'NOT the covalent bonds' point is the most commonly missed mark.
Question 6
Paper 4 (Extended) data-trend style6 marks
The simple molecular substances $\text{Cl}_{2}$ , $\text{Br}_{2}$ and $\text{I}_{2}$ have increasing boiling points in that order. Explain this trend in terms of molecular size and the forces involved. (6 marks)
Model answer
All three substances are simple molecular and exist as diatomic molecules held to one another by weak intermolecular forces. As you move from $\text{Cl}_{2}$ to $\text{Br}_{2}$ to $\text{I}_{2}$ , the relative molecular mass ( $M_{\text{r}}$ ) increases and the molecules become larger. Larger molecules have stronger intermolecular forces between them. To boil each substance, these intermolecular forces must be overcome, and stronger forces require more energy to break. Therefore more energy (a higher temperature) is needed to boil the larger molecules, so the boiling point increases from chlorine to bromine to iodine. Throughout, the strong covalent bonds inside the molecules are not broken — only the forces between molecules are overcome.
Why this scores
Six marks: all simple molecular; $M_{\text{r}}$ /size increases down the order; larger molecules → stronger intermolecular forces; boiling overcomes intermolecular forces; stronger forces need more energy; so boiling point increases. Bonus credit for noting the covalent bonds are not broken.

Key Definitions and Keywords — Simple Molecules and Covalent Bonds

Definitions to memorise and the exact keywords mark schemes credit for simple molecules and covalent bonds answers — sharpened from recent examiner reports for the 2026 0620 sitting.

Covalent bond
Examiner keyword
A shared pair of electrons between two non-metal atoms.
Simple molecular substance
Examiner keyword
A substance made of small, discrete molecules held to one another by weak intermolecular forces.
Intermolecular forces
Examiner keyword
The WEAK forces of attraction BETWEEN molecules. These (not the covalent bonds) are overcome when a simple molecular substance melts or boils.
Double / triple bond
Examiner keyword
Two shared pairs of electrons (double, e.g. $\text{O}_{2}$ , $\text{CO}_{2}$ ) or three shared pairs (triple, e.g. $\text{N}_{2}$ ) between two atoms.
Lone pair
A pair of outer electrons on an atom that is NOT involved in a bond (e.g. two lone pairs on the O in $\text{H}_{2}\text{O}$ ).

Common Mistakes and Misconceptions — Simple Molecules and Covalent Bonds

The traps other students keep falling into on simple molecules and covalent bonds questions — taken from recent Cambridge IGCSE 0620 examiner reports and mark schemes — and how to avoid them.

✕Saying simple molecular substances have low melting points because they have weak covalent bonds.
0620/42 — recurring
Why it happens
Confusing the covalent bonds INSIDE molecules with the forces BETWEEN molecules.
How to avoid it
Covalent bonds are STRONG. The low melting/boiling point is due to WEAK INTERMOLECULAR FORCES between molecules being overcome — the covalent bonds inside the molecules are NOT broken.
✕Saying simple molecular substances conduct electricity when molten.
Why it happens
Generalising from ionic compounds, which conduct when molten.
How to avoid it
Simple molecular substances have NO free electrons and NO ions, so they do not conduct in any state.
✕Drawing electrons being transferred (gained/lost) in a covalent bond.
Why it happens
Mixing covalent bonding up with ionic bonding.
How to avoid it
Covalent bonding is SHARING a pair of electrons that sits between the two atoms — nothing is transferred.
✕Drawing 8 electrons around a hydrogen atom.
Why it happens
Over-applying the octet rule.
How to avoid it
Hydrogen is stable with just 2 outer electrons (helium configuration), so it forms only one single bond.

Simple Molecules and Covalent Bonds — frequently asked questions

The things students keep getting wrong in this sub-topic, answered.

Covalent bond. A SHARED pair of electrons between two non-metal atoms.

Why share? Each atom is closer to a full outer shell (a noble-gas configuration). The shared electrons COUNT for BOTH atoms.

Worked: H₂ (hydrogen molecule).

Each H atom has 1 electron (config: 1).
They share both → each H 'sees' 2 electrons → like helium (full 1st shell).
Forms a single covalent bond H–H.

Each H now counts two electrons in its shell — the helium configuration — by sharing one pair.

Worked: H₂O (water).

O has 6 outer e⁻; needs 2 more for full shell.
Each H shares 1 e⁻ with O.
O ends up with 8 (full); each H ends up with 2 (full).

Multiple bonds.

Single (1 pair shared): H₂, HCl, H₂O.
Double (2 pairs): O=O, CO₂ (each O double bonds to C: O=C=O).
Triple (3 pairs): N≡N (very strong; why N₂ is so unreactive).

Each extra shared pair adds another line to the bond — and makes the bond stronger.

Diagram conventions. Dots and crosses to distinguish electrons from each atom. A bond = a pair (one dot + one cross) between two atoms.

Each bond is one shared pair; O reaches 8 outer electrons and each H reaches 2.

Cambridge tip. Always count BOTH the dots and crosses around an atom; should equal noble-gas configuration (2, 8, 8) when the molecule is correctly drawn.

Property

Simple molecular substance

Reason

Melting / boiling point

Low — often gases (O₂, N₂, CO₂) or liquids (H₂O, ethanol) at room temperature

Only the weak forces between molecules need to be overcome

Electrical conductivity

Does not conduct as a solid, liquid or in solution

No free electrons and no free ions

Solubility in water

Some soluble (sugar, ethanol); others insoluble (oils, hexane)

Polar molecules dissolve in water; non-polar ones do not

Simple Molecules and Covalent Bonds

Short Notes - Simple Molecules and Covalent Bonds

Detailed Study Notes

At a glance

What you’ll learn

What is a covalent bond?

Properties of simple molecular substances

Quick recap

Memorise this

How it’s examined

Take this whole topic with you

1Define a covalent bond in Cambridge wording

2Dot-and-cross of H2\text{H}_{2}H2​

3Dot-and-cross of H2O\text{H}_{2}\text{O}H2​O

4Triple bond in N2\text{N}_{2}N2​

5Why simple molecular substances have low melting/boiling points

6Relating MrM_{\text{r}}Mr​ to boiling point

Covalent bond

Simple molecular substance

Intermolecular forces

Double / triple bond

Lone pair

✕Saying simple molecular substances have low melting points because they have weak covalent bonds.

✕Saying simple molecular substances conduct electricity when molten.

✕Drawing electrons being transferred (gained/lost) in a covalent bond.

✕Drawing 8 electrons around a hydrogen atom.

Simple Molecules and Covalent Bonds — frequently asked questions

Simple Molecules and Covalent Bonds

Short Notes - Simple Molecules and Covalent Bonds

Detailed Study Notes

At a glance

What you’ll learn

What is a covalent bond?

Properties of simple molecular substances

Quick recap

Memorise this

How it’s examined

Take this whole topic with you

1Define a covalent bond in Cambridge wording

2Dot-and-cross of H2\text{H}_{2}H2​

3Dot-and-cross of H2O\text{H}_{2}\text{O}H2​O

4Triple bond in N2\text{N}_{2}N2​

5Why simple molecular substances have low melting/boiling points

6Relating MrM_{\text{r}}Mr​ to boiling point

Covalent bond

Simple molecular substance

Intermolecular forces

Double / triple bond

Lone pair

✕Saying simple molecular substances have low melting points because they have weak covalent bonds.

✕Saying simple molecular substances conduct electricity when molten.

✕Drawing electrons being transferred (gained/lost) in a covalent bond.

✕Drawing 8 electrons around a hydrogen atom.

Simple Molecules and Covalent Bonds — frequently asked questions

2Dot-and-cross of $\text{H}_{2}$

3Dot-and-cross of $\text{H}_{2}\text{O}$

4Triple bond in $\text{N}_{2}$

6Relating $M_{\text{r}}$ to boiling point

2Dot-and-cross of $\text{H}_{2}$

3Dot-and-cross of $\text{H}_{2}\text{O}$

4Triple bond in $\text{N}_{2}$

6Relating $M_{\text{r}}$ to boiling point