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GCSE Chemistry · GCSEChapter 5 · Covalent bonding, simple and giant structures
GCSE · Chapter 5

Covalent bonding, simple and giant structures

By the end of this chapter you will be able to

  • Draw dot-and-cross diagrams for H2, HCl, H2O, NH3, CH4 and CO2
  • Explain why simple molecular substances have low melting points and do not conduct
  • Compare the structures, hardness and melting points of diamond and silicon dioxide
  • Explain why graphite conducts and why it is soft, and give uses of graphene and fullerenes
  • [H] Explain intermolecular forces, and why they are weak compared with covalent bonds

You should already know

  • Electron arrangement and outer electrons (Chapter 2)
  • Ionic bonding and dot-and-cross diagrams (Chapter 4)

Where this leads

  • Metallic bonding and nanoparticles (Chapter 6)
  • Relative formula mass of molecules (Chapter 7)
  • Crude oil and hydrocarbons (Chapter 15)

GCSE Chemistry. Content follows the GCSE (9-1) subject content for England (Edexcel and AQA). Content references: Describe covalent bonds as shared pairs of electrons, and draw dot-and-cross diagrams for small molecules, Describe simple molecular substances and explain their properties, Describe giant covalent structures (diamond, silicon dioxide) and their properties, Describe the structure and uses of graphite, graphene and fullerenes, [H] Explain intermolecular forces and why they are weak.

Exercise P  Do you remember?

1
FHow many outer electrons does a carbon atom have? Write the number.
2
FHow many outer electrons does an oxygen atom have? Write the number.
3
FWhich type of bond holds ions together in sodium chloride? Write the word.
4
FWrite the formula of methane. Write the formula.
5
FWhat is 4 + 4 + 2? Write the number.
5.1

Covalent bonds and dot-and-cross diagrams

GCSE
Describe covalent bonds as shared pairs of electrons, and draw dot-and-cross diagrams for small molecules
Video lesson: Covalent bonds and dot-and-cross diagramsComing soon
Context. A pupil builds models of molecules with coloured balls and sticks. “Why does oxygen make two sticks and hydrogen only one?” she asks. Each stick is a shared pair of electrons, and the number of sticks depends on how many electrons an atom needs.

A covalent bond forms when two atoms share a pair of electrons, so that both atoms have full outer shells. Non-metal atoms form covalent bonds with each other. A molecule is a group of atoms held together by covalent bonds. In a dot-and-cross diagram, each shared pair has one dot (from one atom) and one cross (from the other). The unshared electrons are lone pairs.

OHH××H<sub>2</sub>O: two shared pairs, 2 lone pairs on O
Water, H2O: two shared pairs and two lone pairs on oxygen
CHHHH××××CH<sub>4</sub>: four shared pairs
Methane, CH4: four shared pairs
OCO××××××××CO<sub>2</sub>: two double bonds (4 shared pairs), lone pairs on O
Carbon dioxide, CO2: two double bonds
NHHH×××NH<sub>3</sub>: three shared pairs, 1 lone pair on N
Ammonia, NH3: three shared pairs and one lone pair on nitrogen

Key ideas

  • A covalent bond is a shared pair of electrons between two non-metal atoms.
  • Each atom in a molecule has a full outer shell: 8 electrons (or 2 for hydrogen).
  • H makes 1 bond, O makes 2, N makes 3, C makes 4, Cl makes 1.
  • Double bonds share two pairs of electrons; CO2 has two double bonds.
Worked example 5.1.1
How many covalent bonds does a nitrogen atom make in ammonia, NH3? Write the number.

Method. Count the hydrogen atoms bonded to nitrogen.

  1. Count. There are three H atoms in NH3, each bonded to the N.
    3 H atoms
  2. Bonds. Each H is one shared pair, so there are 3 bonds.
    3 bonds
  3. Write the answer.
    3

Check. Nitrogen has 5 outer electrons: 3 shared, 2 left as a lone pair. ✓

Worked example 5.1.2
How many shared pairs are there in one molecule of carbon dioxide? Write the number.

Method. Count the bonds in the double bonds.

  1. Look. CO2 has two double bonds, one on each side of the carbon.
    two double bonds
  2. Count. Each double bond has two shared pairs, so 2 x 2 = 4.
    2 x 2 = 4
  3. Write the answer.
    4

Check. The carbon shares 8 electrons in total. ✓

Worked example 5.1.3
How many lone pairs of electrons are on the oxygen atom in water? Write the number.

Method. Oxygen has 6 outer electrons.

  1. Shared. Oxygen shares 2 electrons in each bond, so 2 pairs are shared.
    2 bonds
  2. Lone. 6 - 2 = 4 electrons are left, so 4 / 2 = 2 lone pairs.
    2 lone pairs
  3. Write the answer.
    2

Check. The oxygen has 2 bonding pairs and 2 lone pairs. ✓

Watch out

Watch out: a covalent bond is a shared pair, and it is different from an ionic bond. Do not draw the electrons on one atom only, and do not draw a metal in a covalent molecule.

Exam tip

Exam tip. When you draw a dot-and-cross diagram, count the outer electrons first. Each atom must end with 8 (or 2 for hydrogen).

Exercise 5A  Covalent bonds and dot-and-cross diagrams

1
FWhat is a covalent bond? Write the words.
2
FHow many covalent bonds does a hydrogen atom make? Write the number.
3
FHow many covalent bonds does an oxygen atom make in water? Write the number.
4
FHow many covalent bonds does a carbon atom make in methane? Write the number.
5
FHow many lone pairs does a nitrogen atom have in ammonia? Write the number.
6
FHow many shared pairs are there in one molecule of hydrogen chloride, HCl? Write the number.
7
FHow many electrons are in the outer shell of carbon in a molecule of methane? Write the number.
8
FHow many shared pairs are there in a molecule of oxygen, O2? Write the number.
9
PSDraw a diagram of H2. Write the number of shared pairs and the number of lone pairs. Write two numbers, shared then lone.
10
PSCount the bonds in one molecule of NH3, and the bonds on the nitrogen. Write one number. Accept 3.
11
RExplain why a molecule of water has bonds but is not an ionic compound, in one sentence. Accept any sentence that says the atoms share electrons in covalent bonds rather than transferring them.
12
RExplain why a double bond is needed in carbon dioxide, using the number of outer electrons, in one or two sentences. Accept any answer that says each O needs 2 more electrons, and sharing 2 pairs with the carbon fills both shells.
5.2

Simple molecular substances

GCSE
Describe simple molecular substances and explain their properties
Video lesson: Simple molecular substancesComing soon
Context. A student heats a small crystal of iodine and it melts, and then it becomes a gas. “Why is iodine so easy to melt, when the bonds inside the molecule are strong?” she asks. The answer is that the forces between the molecules are weak.

A simple molecular substance is made of molecules, each with a fixed number of atoms joined by strong covalent bonds. The molecules are held together by weak intermolecular forces. Simple molecular substances have low melting and boiling points, because only a little energy is needed to separate the molecules. They do not conduct electricity, because they have no free electrons and no ions.

SubstanceMelting pointConducts electricity?Why
iodine, water, CO2 (simple molecular)lownoweak forces between molecules, not covalent bonds
diamondvery highnoa giant covalent lattice; no free electrons
graphitevery highyesdelocalised electrons between layers
silicon dioxidevery highnoa giant covalent lattice; all electrons are in bonds
Simple molecular substances compared with giant structures

Key ideas

  • Simple molecular: small molecules with strong covalent bonds inside them and weak forces between them.
  • Low melting and boiling points, because the weak forces are easy to overcome.
  • Do not conduct electricity: no free electrons and no ions.
  • Melting breaks the forces between molecules, not the covalent bonds.
Worked example 5.2.1
Why does iodine have a low melting point? Write the words.

Method. Think about what is broken on melting.

  1. Look. Iodine is simple molecular, with weak forces between molecules.
    weak forces
  2. Conclude. Only the weak forces need to be broken, so little energy is needed.
    little energy
  3. Write the answer.
    weak forces between molecules

Check. The covalent bonds inside the molecules are not broken. ✓

Worked example 5.2.2
Does a simple molecular substance conduct electricity when solid? Write yes or no.

Method. Check for charged particles that can move.

  1. Look. Simple molecular substances have no free electrons and no ions.
    no free electrons
  2. Decide. So they do not conduct.
    no
  3. Write the answer.
    no

Check. Water is a simple molecular substance and is a poor conductor. ✓

Worked example 5.2.3
Why do simple molecular substances have low boiling points? Write one reason.

Method. Think about the forces.

  1. Look. Boiling separates the molecules from each other.
    separates molecules
  2. Conclude. The forces between the molecules are weak, so little energy is needed.
    weak forces
  3. Write the answer.
    the forces between molecules are weak

Check. The molecules themselves do not split during boiling. ✓

Watch out

Watch out: when a simple molecular substance melts or boils, the covalent bonds inside the molecules are not broken. Only the weak forces between molecules are overcome.

Exam tip

Exam tip. Say “weak forces between molecules” or “intermolecular forces”, not “weak bonds”.

Exercise 5B  Simple molecular substances

1
FWhat holds the atoms together inside a molecule? Write the words.
2
FAre the forces between molecules strong or weak? Write the word.
3
FDo simple molecular substances have high or low melting points? Write the word.
4
FDoes a simple molecular substance contain free electrons? Write yes or no.
5
FName a simple molecular substance that is a liquid at room temperature. Write the name.
6
FName a simple molecular substance that is a gas at room temperature. Write the name. Accept any of: CO2, CH4, O2, NH3.
7
FWhat is the name of the forces that act between molecules? Write the words.
8
FDoes iodine conduct electricity as a solid? Write yes or no.
9
RExplain why a simple molecular substance has a low melting point, in one sentence. Accept any sentence that says the weak forces between molecules are easily overcome.
10
RA pupil says, “Iodine melts easily because its covalent bonds are weak.” Explain why this is wrong, in one sentence. Accept any sentence that says the covalent bonds are strong, and the weak forces between molecules are what melt.
11
PSExplain why a simple molecular substance does not conduct, in one sentence. Accept any sentence that says it has no ions or free electrons to carry charge.
12
PSPredict whether a substance made of simple molecules, with a melting point of 50 degrees C, is a solid or a gas at 20 degrees C. Write the word.
13
RPredict whether a simple molecular substance dissolves in water. Write one sentence. Accept any answer that says it depends on the substance, and do not use its ions.
5.3

Giant covalent structures: diamond and silicon dioxide

GCSE
Describe giant covalent structures (diamond, silicon dioxide) and their properties
Video lesson: Giant covalent structures: diamond and silicon dioxideComing soon
Context. A jeweller cuts a diamond with a diamond-tipped saw. “Why does a diamond scratch glass, and why does it not melt easily?” asks a visitor. The answer is in its structure: every carbon atom is joined to four others by covalent bonds, in one giant lattice.

A giant covalent structure is a huge network of atoms, each joined to its neighbours by strong covalent bonds. In diamond, each carbon atom is bonded to four others. In silicon dioxide (silica), each silicon atom is bonded to four oxygen atoms, and each oxygen to two silicon atoms. Because all the atoms are held by strong covalent bonds, these substances have very high melting points and are very hard. They do not conduct, because there are no free electrons.

Diamond: each carbon bonded to 4 otherssimplified 2D drawing: every atom is joined to 4 others in 3D
Diamond: a giant covalent lattice (simplified)
Silicon dioxide: a giant covalent lattice of Si and OSiOSiOSiOSiOSiOSiOSiOSisimplified: each Si is bonded to 4 O atoms, each O to 2 Si
Silicon dioxide: a giant covalent lattice (simplified)
StructureExampleBondingMelting point
simple molecularH2O, CH4strong covalent bonds inside molecules, weak forces between themlow
giant covalentdiamond, SiO2strong covalent bonds in a giant latticevery high
giant ionicNaClelectrostatic attraction in a latticehigh
Simple molecular, giant covalent and giant ionic structures compared

Key ideas

  • Giant covalent structures have strong covalent bonds throughout the lattice.
  • Very high melting points: many strong bonds must be broken.
  • Diamond and silicon dioxide are very hard.
  • They do not conduct electricity, because they have no free electrons (in diamond and silicon dioxide).
Worked example 5.3.1
Why does diamond have a very high melting point? Write the words.

Method. Think about the bonds that must be broken.

  1. Look. Diamond is a giant lattice of carbon atoms, joined by strong covalent bonds.
    giant lattice
  2. Conclude. A lot of energy is needed to break many strong bonds, so the melting point is very high.
    many strong bonds
  3. Write the answer.
    many strong covalent bonds must be broken

Check. Simple molecular substances are much lower. ✓

Worked example 5.3.2
Which is more like the melting point of diamond: iodine or silicon dioxide? Write the name. Use the values 114 and 1710 degrees C.

Method. Compare with the two values.

  1. Compare. Diamond melts at about 3550 degrees C, a very high value.
    3550
  2. Decide. Silicon dioxide, at about 1710 degrees C, is much closer to diamond than iodine at 114 degrees C.
    1710 is closer
  3. Write the answer.
    silicon dioxide

Check. Both are giant covalent structures. ✓

Worked example 5.3.3
Name the type of structure of silicon dioxide. Write the words.

Method. Recall the type of structure.

  1. Recall. Silicon dioxide is a giant covalent structure.
    giant covalent
  2. Check. It is not a simple molecular substance, because it has no separate molecules.
    no molecules
  3. Write the answer.
    giant covalent structure

Check. Sand is mostly silicon dioxide. ✓

Watch out

Watch out: diamond and silicon dioxide are giant covalent structures, not simple molecular substances. Their melting points are very high because many strong bonds must be broken, not because of weak forces.

Exam tip

Exam tip. Use the words “giant lattice” and “strong covalent bonds” in answers about melting points and hardness.

Exercise 5C  Giant covalent structures: diamond and silicon dioxide

1
FHow many other carbon atoms is each carbon atom in diamond bonded to? Write the number.
2
FWhat is the type of structure of diamond? Write the words.
3
FIs diamond a good conductor of electricity? Write yes or no.
4
FWhat is the formula of silicon dioxide? Write the formula.
5
FIs silicon dioxide hard or soft? Write the word.
6
FHow many oxygen atoms is each silicon atom bonded to in silicon dioxide? Write the number.
7
FWhich is more likely to have a very high melting point: a giant covalent structure or a simple molecular substance? Write the words.
8
RExplain why diamond is hard, in one sentence. Accept any sentence that says every atom is held in a giant lattice by strong covalent bonds.
9
RExplain why diamond has a much higher melting point than iodine, in one or two sentences. Accept any answer that says diamond needs many strong covalent bonds broken, while iodine needs only the weak forces overcome.
10
RA pupil says diamond conducts electricity because it is made of carbon. Explain why this is wrong, in one sentence. Accept any sentence that says all of diamond’s electrons are in bonds, so there are no free electrons.
5.4

Graphite, graphene and fullerenes

GCSE
Describe the structure and uses of graphite, graphene and fullerenes
Video lesson: Graphite, graphene and fullerenesComing soon
Context. A pupil writes with a pencil and the mark stays on the paper. “Pencil lead is made of carbon, so why is it soft when diamond is so hard?” she asks. The answer is that graphite has a different structure, with layers that slide over each other.

Graphite is another form of carbon. Each carbon atom is bonded to three others in flat hexagonal layers. Each carbon has one outer electron that is not used in a bond, and these delocalised electrons can move along the layers, so graphite conducts electricity. The layers are held by weak forces, so they slide over each other, and graphite is soft and slippery. It is used in pencils and as a lubricant.

Graphene is a single layer of graphite, one atom thick. It is very strong, light and conducts electricity. Fullerenes are hollow molecules of carbon, such as C60, which is shaped like a football. They are used in lubricants and in nanotechnology.

Graphite: layers of hexagons with delocalised electronslayers slide over each other; blue-purple dots: delocalised electrons between layers
Graphite: layers of hexagons, with delocalised electrons between them (simplified)
Graphene: one layer, one atom thickstrong, very thin, and conducts electricity
Graphene: a single layer of carbon atoms (simplified)
Fullerene (buckminsterfullerene, C60)a hollow cage of 60 carbon atoms (simplified)
Fullerene C60 (simplified)
PropertyDiamondGraphite
bonds per carbon4 covalent3 covalent in each layer
structuretetrahedral latticelayers of hexagons
hardnessvery hardsoft; layers slide over each other
electrical conductor?noyes: delocalised electrons
usecutting toolspencil leads, lubricant, electrodes
Diamond and graphite compared

Key ideas

  • Graphite: each carbon bonded to three others in layers; delocalised electrons allow it to conduct.
  • The layers in graphite slide over each other, so it is soft and used as a lubricant.
  • Graphene: one layer of graphite; strong, light and a good conductor.
  • Fullerenes: hollow carbon molecules such as C60; used in lubricants and nanotechnology.
Worked example 5.4.1
Why does graphite conduct electricity? Write the words.

Method. Look for particles that can move.

  1. Look. Each carbon has one delocalised electron that is not used in bonds.
    delocalised electron
  2. Conclude. These electrons move along the layers and carry a current.
    carry a current
  3. Write the answer.
    it has delocalised electrons that can move

Check. Diamond has no delocalised electrons. ✓

Worked example 5.4.2
Why is graphite soft? Write the words.

Method. Think about the forces between the layers.

  1. Look. The layers are held together by weak forces.
    weak forces
  2. Conclude. So the layers slide over each other easily.
    slide
  3. Write the answer.
    the layers are held by weak forces and slide over each other

Check. Diamond is hard because every atom is held in a giant lattice. ✓

Worked example 5.4.3
How many outer electrons in each carbon atom of graphite are not used in bonds? Write the number.

Method. Count the bonds each carbon makes.

  1. Bonds. Each carbon makes three covalent bonds in graphite.
    3 bonds
  2. Left over. Carbon has 4 outer electrons, so 4 - 3 = 1 is left over.
    1
  3. Write the answer.
    1

Check. The one leftover electron is delocalised. ✓

Watch out

Watch out: graphite and diamond are both carbon, but they have different structures. Graphite conducts because of delocalised electrons; diamond does not conduct because all its electrons are in bonds.

Exam tip

Exam tip. When you compare graphite and diamond, mention the bonds per carbon atom, the structure, and one property with its reason.

Exercise 5D  Graphite, graphene and fullerenes

1
FHow many other carbon atoms is each carbon atom in graphite bonded to? Write the number.
2
FDoes graphite conduct electricity? Write yes or no.
3
FWhat are the electrons that can move in graphite called? Write the words.
4
FIs graphite soft or hard? Write the word.
5
FName one use of graphite. Write the use. Accept any of: pencil lead, lubricant, electrodes.
6
FWhat is graphene? Write the words.
7
FHow many atoms are in one molecule of C60? Write the number.
8
FWhat shape is a fullerene like C60? Write the word.
9
RExplain why graphite can be used as a lubricant, in one sentence. Accept any sentence that says the layers slide over each other easily.
10
RCompare graphite and diamond in one sentence, giving one difference in structure. Accept any sentence that says graphite has layers of hexagons, while diamond has a 3D lattice of four bonds per carbon.
11
PSExplain why graphene is strong and conducts electricity, in one sentence. Accept any sentence that says it has strong covalent bonds and delocalised electrons that can move.
5.5

Intermolecular forces [H]

GCSE
[H] Explain intermolecular forces and why they are weak
Video lesson: Intermolecular forces [H]Coming soon
Context. A chemist compares the melting point of water with the melting point of a salt. “The water molecules are held by strong bonds,” she says, “but its melting point is much lower.” Her point is about the forces between molecules, which are much weaker than the bonds inside them.

[H] Higher tier only. Intermolecular forces are the weak attractions between neighbouring molecules. They are much weaker than covalent bonds, so they are easy to overcome. When a simple molecular substance melts or boils, these forces are broken; the covalent bonds inside the molecules stay intact.

Weak forces between simple molecules (intermolecular forces)the covalent bonds inside each molecule are strong, but the forces between molecules are weak
Weak forces (dashed) between neighbouring molecules

Key ideas

  • Intermolecular forces are the weak attractions between molecules.
  • They are much weaker than covalent bonds.
  • Melting and boiling simple molecular substances overcome intermolecular forces, not covalent bonds.
  • The bigger the molecule, the stronger the forces, and the higher the boiling point, in general.
Worked example 5.5.1
[H] What type of force is broken when iodine melts? Write the words.

Method. Think about what separates the molecules.

  1. Look. Melting separates the molecules from each other.
    separates
  2. Conclude. So the forces broken are intermolecular forces.
    intermolecular forces
  3. Write the answer.
    intermolecular forces

Check. The iodine molecules themselves stay intact. ✓

Worked example 5.5.2
[H] Are covalent bonds stronger or weaker than intermolecular forces? Write the word.

Method. Compare the strength of the two.

  1. Compare. Covalent bonds are strong; intermolecular forces are weak.
    strong vs weak
  2. Decide. So covalent bonds are stronger.
    stronger
  3. Write the answer.
    stronger

Check. Covalent bonds need much more energy to break. ✓

Worked example 5.5.3
[H] Why does the melting point of a larger molecule tend to be higher? Write one reason.

Method. Think about the surface of the molecule.

  1. Look. A larger molecule has more surface for forces to act on.
    more surface
  2. Conclude. So the forces between molecules are stronger, and more energy is needed.
    stronger forces
  3. Write the answer.
    larger molecules have stronger intermolecular forces

Check. Accept any answer with stronger forces for bigger molecules. ✓

Watch out

Watch out: a covalent bond is inside a molecule, and an intermolecular force is between molecules. Only the second is broken when a simple molecular substance melts or boils.

Exam tip

Exam tip. When a question says “melting”, name the forces between molecules, not the covalent bonds.

Exercise 5E  Intermolecular forces [H]

1
F[H] What are the weak attractions between molecules called? Write the words.
2
F[H] Are intermolecular forces stronger or weaker than covalent bonds? Write the word.
3
F[H] When iodine boils, which bonds are broken: covalent or intermolecular? Write the word.
4
R[H] Explain why a simple molecular substance has a low boiling point, in one sentence. Accept any sentence that says only weak intermolecular forces need to be overcome.
5
PS[H] Explain why water has a higher boiling point than methane, using intermolecular forces. Write one or two sentences. Accept any answer that says water molecules have stronger intermolecular forces between them.
6
R[H] Explain why the melting point of iodine is low, even though the I-I covalent bond is strong, in one sentence. Accept any sentence that says the weak forces between molecules are overcome, not the strong covalent bond.

Chapter summary

SkillMethod
Covalent bondA shared pair of electrons between two non-metal atoms.
Dot-and-crossOne dot or cross from each atom in each shared pair; lone pairs are left on the atom.
Simple molecularLow melting points; weak forces between molecules; do not conduct.
Giant covalentA lattice of strong covalent bonds: diamond and silicon dioxide; very high melting points.
GraphiteLayers of hexagons; delocalised electrons conduct; layers slide, so it is soft.
Graphene and fullerenesGraphene: one layer, strong, conducts. Fullerenes: hollow carbon molecules such as C60.
[H] Intermolecular forcesWeak forces between molecules; overcome on melting and boiling, not covalent bonds.

Can you…?

  • I can draw dot-and-cross diagrams for small covalent molecules
  • I can explain the properties of simple molecular substances
  • I can describe the structures of diamond and silicon dioxide, and explain their properties
  • I can explain why graphite conducts and is soft, and give uses of graphene and fullerenes
  • [H] I can explain intermolecular forces and why they are weak

Key terms

covalent bond
a shared pair of electrons between two atoms
molecule
a group of atoms joined by covalent bonds
lone pair
a pair of outer electrons on an atom that are not shared
simple molecular substance
a substance made of molecules held by weak intermolecular forces
giant covalent structure
a giant network of atoms joined by strong covalent bonds
delocalised electron
an electron that is free to move, such as the one in each carbon of graphite
fullerene
a hollow molecule of carbon atoms, such as C60
intermolecular force
[H] a weak attraction between neighbouring molecules

Exercise 5Z  Check-up

1
How many covalent bonds does a nitrogen atom make in ammonia? Write the number.
2
How many lone pairs are on the oxygen atom in water? Write the number.
3
What is the type of bond in a molecule of hydrogen chloride? Write the word.
4
Is a simple molecular substance a good conductor when solid? Write yes or no.
5
What forces are overcome when a simple molecular substance melts? Write the words.
6
Name a giant covalent structure. Write the name. Accept diamond or silicon dioxide.
7
Does graphite conduct electricity? Write yes or no.
8
Give one use of graphene or fullerenes. Accept any reasonable use, such as lubricant, strong material or electronics.
9
Explain why diamond has a very high melting point, in one sentence. Accept any sentence that says many strong covalent bonds must be broken.

Total 23 marks. Allow about 23 minutes.

Exercise 5X  Exam-style questions

1
FDraw or describe the dot-and-cross diagram for hydrogen chloride, HCl, and state how many shared pairs it has. Write the number.[2 marks]
2
RExplain why iodine has a low melting point, in one or two sentences. Accept any answer that says the weak intermolecular forces between molecules are overcome.[3 marks]
3
RExplain why graphite conducts electricity but diamond does not, in two sentences. Accept any answer that says graphite has delocalised electrons, and diamond has all its electrons in bonds.[4 marks]
4
RDescribe the structure of silicon dioxide, in one sentence. Accept any sentence that says it is a giant lattice of silicon and oxygen atoms joined by covalent bonds.[2 marks]
5
PSGive the number of shared pairs in one molecule of carbon dioxide, and explain why there are that many. Write the number, then one sentence. Accept 4, with a reason that there are two double bonds.[3 marks]
6
RDescribe the difference between a covalent bond and an intermolecular force, in one or two sentences. Accept any answer that says a covalent bond is a shared pair inside a molecule, and an intermolecular force is a weak attraction between molecules.[3 marks]
7
FName the type of structure that diamond and silicon dioxide have. Write the words.[1 mark]
8
RA pupil says “Diamond is soft because it is carbon.” Explain why this is wrong, in one sentence. Accept any sentence that says diamond is a rigid giant lattice of strong bonds, which makes it hard.[2 marks]
9
PSPredict whether a simple molecular substance with a melting point of 50 degrees C is a liquid or a gas at 60 degrees C. Write the word, and say why in one sentence. Accept gas, because 60 is above the boiling point; or liquid if the boiling point is above 60. Accept any sensible reason based on the melting point.[3 marks]
← Chapter 4: Ionic bonding and ionic compoundsChapter 6: Metallic bonding, alloys and nanoparticles →

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