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GCSE Chemistry · GCSEChapter 6 · Metallic bonding, alloys and nanoparticles
GCSE · Chapter 6

Metallic bonding, alloys and nanoparticles

By the end of this chapter you will be able to

  • Describe metallic bonding and explain why metals conduct and are malleable
  • Explain why an alloy is harder than the pure metal it is based on
  • Give the size range of nanoparticles and examples of their uses
  • Discuss a benefit and a risk of using nanoparticles, using evidence
  • [H] Explain the surface area effect with a calculation

You should already know

  • Ionic and covalent bonding (Chapters 4 and 5)
  • Standard form and units of length (Chapter 1)

Where this leads

  • Cathodes and electrolysis of metals (Chapter 11)
  • Extraction and recycling of metals (Chapter 19)
  • Catalysts and surface area in reactions (Chapter 13)

GCSE Chemistry. Content follows the GCSE (9-1) subject content for England (Edexcel and AQA). Content references: Describe metallic bonding as a lattice of positive ions in delocalised electrons, and the properties of metals, Explain why alloys are harder than pure metals, and give examples of alloys and their uses, Describe the size of nanoparticles and their uses, and discuss their risks, [H] Explain how the surface area to volume ratio affects the properties of nanoparticles.

Exercise P  Do you remember?

1
FWhat is the charge of an electron? Write the sign and number.
2
FWhich group of the periodic table do the alkali metals belong to? Write the number.
3
FWhich bond holds ions together in an ionic compound? Write the word.
4
FHow many metres are in one millimetre? Write the answer in standard form.
5
FWhat is 1 / 1000 of 5 000? Write the number.
6.1

Metallic bonding and the properties of metals

GCSE
Describe metallic bonding as a lattice of positive ions in delocalised electrons, and the properties of metals
Video lesson: Metallic bonding and the properties of metalsComing soon
Context. A pupil bends a copper wire into a loop and it stays bent. He taps a sheet of aluminium into shape with a hammer. “Why can metals be bent and hammered, but salt crystals shatter?” he asks. The answer is in metallic bonding.

In a metal, the outer electrons of each atom are delocalised: they are free to move through the whole structure. The metal atoms become positive ions, arranged in a regular lattice. The positive ions are attracted to the sea of delocalised electrons, and this attraction is the metallic bond.

Metallic bonding: a lattice of positive ions in a sea of electrons++++++++++++++++++++++++positive ions (+) and delocalised electrons (blue dots)
Metallic bonding: positive ions in a sea of delocalised electrons (not to scale)
Property of metalsExplanation
conduct electricity and heatdelocalised electrons move through the lattice
malleable (can be bent or hammered)layers of ions can slide over each other
high melting pointsstrong attraction between the ions and the electrons
shinythe delocalised electrons reflect light
The properties of metals and their explanations

Key ideas

  • Metallic bonding: strong attraction between positive ions and delocalised electrons.
  • Metals conduct electricity and heat because the delocalised electrons move.
  • Metals are malleable because the layers of ions can slide over each other.
  • Metals have high melting points because the metallic bond is strong.
Worked example 6.1.1
Why can metals conduct electricity? Write the words.

Method. Think about what carries the current.

  1. Look. Metals have delocalised electrons that are free to move.
    delocalised electrons
  2. Conclude. These electrons carry charge through the metal, so it conducts.
    carry charge
  3. Write the answer.
    the delocalised electrons can move and carry charge

Check. Ionic solids do not conduct when solid, because their ions are fixed. ✓

Worked example 6.1.2
Why are metals malleable? Write the words.

Method. Think about the layers of ions.

  1. Look. The layers of positive ions can move past each other.
    layers move
  2. Conclude. The delocalised electrons stay attracted to the ions, so the metal does not break when it is bent.
    does not break
  3. Write the answer.
    the layers of ions can slide over each other

Check. Ionic solids break because like charges repel. ✓

Worked example 6.1.3
What is the name of the bond between the positive ions and the delocalised electrons? Write the words.

Method. Recall the bond in metals.

  1. Recall. The attraction between the positive ions and the sea of electrons is a metallic bond.
    metallic bond
  2. Check. It is not an ionic bond between separate ions, and not a covalent bond.
    not ionic or covalent
  3. Write the answer.
    metallic bond

Check. It is an electrostatic attraction. ✓

Watch out

Watch out: in a metal, the electrons are delocalised, not fixed to one atom. Do not say that the metal atoms form ions by sharing electrons; they lose outer electrons to the sea.

Exam tip

Exam tip. When you explain a property of a metal, name the particles (ions, delocalised electrons) and say what they do.

Exercise 6A  Metallic bonding and the properties of metals

1
FWhat are the particles in the lattice of a metal? Write the words.
2
FWhat are the electrons called that are free to move in a metal? Write the word.
3
FDo metals conduct electricity? Write yes or no.
4
FAre metals malleable? Write yes or no.
5
FDo metals usually have high or low melting points? Write the word.
6
FWhat type of bond holds the lattice of a metal together? Write the words.
7
FName the property of metals that means they can be drawn into wires. Write the word.
8
FWhich particles carry the electric current in a metal? Write the words.
9
FWhy are metals shiny? Write one reason in words. Accept any reason that says the delocalised electrons reflect light.
10
RExplain why metals conduct heat as well as electricity, in one sentence. Accept any sentence that says the delocalised electrons transfer energy quickly through the lattice.
11
RExplain why an ionic solid shatters when hit, but a metal bends, in one sentence. Accept any sentence that says the layers of metal ions can slide while the electrons keep them bonded, but ionic layers push like charges together.
12
RA pupil says “Metals are soft because their atoms are not bonded.” Explain why this is wrong, in one sentence. Accept any sentence that says the atoms are bonded by metallic bonds.
6.2

Alloys

GCSE
Explain why alloys are harder than pure metals, and give examples of alloys and their uses
Video lesson: AlloysComing soon
Context. A bicycle frame is made of a light alloy, not a pure metal. “Why not use pure aluminium?” asks a pupil. Pure aluminium is soft and bends too easily, but a small amount of other metal changes the structure and makes it stronger.

An alloy is a mixture of a metal with another element, usually another metal. In a pure metal, the layers of atoms can slide over each other. In an alloy, the atoms are of different sizes, so they distort the layers and stop them sliding. This makes the alloy harder and usually stronger than the pure metal.

pure metalalloylayers can slide over each otherdifferent-sized atoms block the layers
Pure metal and an alloy: different-sized atoms stop the layers sliding (not to scale)
AlloyMade fromProperties and uses
steeliron with a little carbonharder and stronger than pure iron
brasscopper and zincharder than copper; used for musical instruments and taps
bronzecopper and tinhard and strong; used for statues and medals
aluminium alloysaluminium with small amounts of other metalslight and strong; used for aircraft and cans
Some common alloys and their uses

Key ideas

  • An alloy is a mixture of a metal with other elements.
  • Different-sized atoms distort the layers of the lattice.
  • The layers cannot slide easily, so alloys are harder and stronger than pure metals.
  • Steel, brass, bronze and aluminium alloys are common examples.
Worked example 6.2.1
Why is steel harder than pure iron? Write the words.

Method. Think about the atoms in steel.

  1. Look. Steel contains carbon atoms, which are a different size from iron atoms.
    different size
  2. Conclude. The different-sized atoms distort the layers, so they slide less easily.
    distort
  3. Write the answer.
    the different-sized carbon atoms distort the layers

Check. Steel is an alloy of iron and carbon. ✓

Worked example 6.2.2
Name the alloy of copper and zinc. Write the name.

Method. Recall the common alloy.

  1. Recall. An alloy of copper and zinc is brass.
    brass
  2. Check. Copper and zinc are both metals, so the mixture is an alloy.
    two metals
  3. Write the answer.
    brass

Check. Brass is harder than copper. ✓

Worked example 6.2.3
Name an alloy that contains copper and tin. Write the name.

Method. Recall the alloy.

  1. Recall. Copper and tin make bronze.
    bronze
  2. Check. Tin is a metal, so copper and tin form an alloy.
    two metals
  3. Write the answer.
    bronze

Check. Bronze is hard and strong. ✓

Watch out

Watch out: an alloy is a mixture of elements, not a compound. The atoms are not chemically joined in a fixed ratio.

Exam tip

Exam tip. When you explain why an alloy is harder, mention the different-sized atoms and the layers that cannot slide.

Exercise 6B  Alloys

1
FWhat is an alloy? Write the words.
2
FIs an alloy harder or softer than the pure metal it is made from? Write the word.
3
FWhat is the main metal in steel? Write the name.
4
FWhat are the two metals in brass? Write the names.
5
FWhat are the two metals in bronze? Write the names.
6
FWhy are alloys usually harder than pure metals? Write the words.
7
FName an alloy that is light and strong, used for aircraft. Write the name.
8
FIs an alloy a compound or a mixture? Write the word.
9
FWhich element is added to iron to make steel? Write the name.
10
PSExplain why a pure metal is softer than an alloy, in one sentence. Accept any sentence that says the atoms in a pure metal are all the same size, so the layers slide.
11
PSGold jewellery is often an alloy. Give one reason why it is not pure gold. Accept any reason that says an alloy is harder and more durable.
12
RExplain why steel is used to make a bridge rather than pure iron, in one or two sentences. Accept any answer that says steel is stronger and harder than iron, because the carbon atoms distort the layers.
13
RExplain why an alloy is still a metal, in one sentence. Accept any sentence that says it still has metallic bonding, delocalised electrons and conducts electricity.
6.3

Nanoparticles: size, uses and risks

GCSE
Describe the size of nanoparticles and their uses, and discuss their risks
Video lesson: Nanoparticles: size, uses and risksComing soon
Context. Sun cream on the label contains “nanoparticles” of zinc oxide. “How small is a nanoparticle, and is it safe to put on the skin?” asks a parent. A nanoparticle is between 1 and 100 nanometres across, which is thousands of times smaller than a grain of sand.

A nanoparticle is a particle between about 1 and 100 nanometres across (1 nm = 10-9 m). Nanoparticles have different properties from larger pieces of the same material, because a larger fraction of their atoms is at the surface. They are used in sunscreens, as catalysts, and in medicine to carry drugs to specific cells. Their risks are still being studied, because some nanoparticles may reach the body or the environment in ways that larger particles do not.

Sizes on a log scale (nanometres)atom (about 0.1 nm)1 nm100 nmred blood cell (about 7000 nm)shaded: the nanoscale, 1 to 100 nm
Sizes compared on a log scale: atoms, nanoparticles and a red blood cell
NanoparticleUseWhy the small size helps
zinc oxide or titanium dioxidesunscreenabsorbs ultraviolet light; does not look white on the skin
gold, iron or platinumcatalystslarge surface area for reactions
variousmedicine deliverycan carry drugs to specific cells
carbonsome electronics and materialsvery strong and small structures
Some uses of nanoparticles and why the small size helps

Key ideas

  • A nanoparticle is between about 1 and 100 nm across.
  • Nanoparticles have a large surface area compared with their volume.
  • Uses: sunscreen (absorbs ultraviolet light), catalysts, medicine delivery.
  • Risks: their effects on the body and the environment are not fully understood, so they are researched and regulated.
Worked example 6.3.1
Write the size range of a nanoparticle, in nanometres. Write the range.

Method. Recall the nanoscale.

  1. Recall. Nanoparticles are between about 1 and 100 nm.
    1 to 100 nm
  2. Check. Atoms are about 0.1 nm, which is smaller than the range.
    smaller than range
  3. Write the answer.
    1 to 100 nm

Check. The atom is about 0.1 nm. ✓

Worked example 6.3.2
Name one use of nanoparticles in sunscreen. Write the name of the substance.

Method. Recall the nanoparticle in sunscreen.

  1. Recall. Zinc oxide nanoparticles are used in sunscreen.
    zinc oxide
  2. Check. Zinc oxide absorbs ultraviolet light, which is the job of sunscreen.
    absorbs UV
  3. Write the answer.
    zinc oxide

Check. They absorb ultraviolet light. ✓

Worked example 6.3.3
Give one possible risk of nanoparticles. Write the words. Accept any reasonable risk, such as harm to the body or the environment.

Method. Think about what is not yet known.

  1. Recall. The effects of nanoparticles on the body and environment are not fully known.
    not fully known
  2. Check. Because the effects are not fully known, research and regulation are needed.
    research needed
  3. Write the answer.
    Accept any reasonable risk, such as harm to the body or the environment.

Check. Scientists research risks before the use is widespread. ✓

Watch out

Watch out: nanoparticles are not automatically dangerous, and not automatically safe. Say what is known, and what is still being researched.

Exam tip

Exam tip. When a question asks about risks, give a balanced answer: a benefit, a risk, and what more research is needed.

Exercise 6C  Nanoparticles: size, uses and risks

1
FWhat is the smallest size of a nanoparticle, in nanometres? Write the number.
2
FWhat is the largest size of a nanoparticle, in nanometres? Write the number.
3
FWrite 1 nm in metres in standard form. Write the answer.
4
FWrite 100 nm in metres in standard form. Write the answer.
5
FWhich metal oxide is used in sunscreen as a nanoparticle? Write the name.
6
FName a metal used as a nanoparticle catalyst. Write the name. Accept gold, iron or platinum.
7
FWhat is nanoscale? Write the words.
8
RExplain why nanoparticles can be used in sunscreen, in one sentence. Accept any sentence that says they absorb ultraviolet light and are small enough to be transparent on skin.
9
RGive one benefit and one risk of using nanoparticles in medicine. Accept any benefit such as delivering drugs to specific cells, and any risk such as effects that are not fully known.
10
RA pupil says, “All nanoparticles are dangerous, so they should never be used.” Explain why this is not a fair conclusion. Accept any answer that says risks must be judged for each use, with evidence.
11
FWrite the word equation: nanoparticles are used as catalysts. What is the function of a catalyst? Write the words.
6.4

Surface area and nanoparticles [H]

GCSE
[H] Explain how the surface area to volume ratio affects the properties of nanoparticles
Video lesson: Surface area and nanoparticles [H]Coming soon
Context. A pupil cuts a cube of sugar into smaller cubes. “The same amount of sugar now has more surface,” she says. Nanoparticles follow the same idea: the same mass of material has a much larger surface area when it is made of very small particles.

[H] Higher tier only. When a solid is divided into smaller pieces, the total surface area increases, but the volume stays the same. A large surface area means more particles at the surface can react or interact, which is why nanoparticles make good catalysts.

one 1 cm cubesurface: 6 cm<sup>2</sup>1000 cubes of 1 mmsurface: 60 cm<sup>2</sup> (ten times more)
One 1 cm cube and 1000 small cubes of the same total volume (not to scale)

Key ideas

  • Cutting a 1 cm cube into 1000 cubes of side 1 mm keeps the same volume (1 cm3).
  • The total surface area rises from 6 cm2 to 60 cm2, ten times more.
  • Nanoparticles have a very large surface area compared with their volume.
  • More surface means a faster reaction when the material is a catalyst.
Worked example 6.4.1
[H] A 1 cm cube has a surface area of 6 cm2. Its volume is 1 cm3. What is the surface area to volume ratio? Write the number.

Method. Divide the surface area by the volume.

  1. Ratio. Ratio = surface area / volume = 6 / 1.
    6 / 1
  2. Answer. So the ratio is 6 per cm.
    6
  3. Write the answer.
    6

Check. The units are cm2 / cm3 = 1/cm. ✓

Worked example 6.4.2
[H] A 1 cm cube is cut into 1000 cubes of side 1 mm. What is the total surface area of all the small cubes, in cm2? Write the number.

Method. Find the area of one small cube, then multiply by 1000.

  1. One cube. Each small cube has 6 faces of 0.1 cm x 0.1 cm = 0.01 cm2, so 6 x 0.01 = 0.06 cm2.
    0.06 cm2
  2. All cubes. Total = 1000 x 0.06 = 60 cm2.
    60
  3. Write the answer.
    60

Check. 60 is ten times 6, the surface of the whole cube. ✓

Worked example 6.4.3
[H] How many times more surface area do the small cubes have than the large cube? Write the number.

Method. Divide the new total by the old.

  1. Divide. New total / old total = 60 / 6.
    60 / 6
  2. Answer. The small cubes have 10 times more surface area.
    10
  3. Write the answer.
    10

Check. The volume stays at 1 cm3. ✓

Watch out

Watch out: cutting a solid does not change its volume, but it does increase the surface area. Keep the units the same, and convert mm to cm first (1 mm = 0.1 cm).

Exam tip

Exam tip. In surface area questions, write the surface area and volume in the same units before dividing.

Exercise 6D  Surface area and nanoparticles [H]

1
F[H] How many faces does a cube have? Write the number.
2
F[H] A cube has side 2 cm. What is the area of one face, in cm2? Write the number.
3
F[H] What is the volume of a cube of side 2 cm, in cm3? Write the number.
4
F[H] How many 1 mm cubes fit in a 1 cm cube? Write the number.
5
F[H] What is the surface area of one 1 mm cube, in mm2? Write the number.
6
PS[H] Convert 6000 mm2 into cm2. Write the number. (1 cm2 = 100 mm2.)
7
PS[H] A 2 cm cube is cut into 8 cubes of side 1 cm. How many times more surface area do the 8 cubes have in total? Write the number.
8
R[H] Explain, in one sentence, why a catalyst made of nanoparticles can work faster than the same mass of large pieces. Accept any sentence that says a larger surface area gives more places for reactions to happen.
9
R[H] Explain why the volume of a solid does not change when it is cut into smaller pieces, in one sentence. Accept any sentence that says the total amount of material stays the same.
6.5

Choosing metals, alloys and nanoparticles

GCSE
Use the properties of metals, alloys and nanoparticles to choose a material for a purpose
Video lesson: Choosing metals, alloys and nanoparticlesComing soon
Context. An engineer must choose a material for an aircraft wing, an electric cable and a jewellery ring. “Which material suits each job?” asks a student. The answer comes from matching the properties to the job.

Materials are chosen by matching their properties to the job. Copper conducts electricity well, so it is used for wires. Aluminium alloys are light and strong, so they are used for aircraft. Gold is unreactive and does not tarnish, so it is used for jewellery, usually as an alloy to make it harder. Nanoparticles are chosen when a large surface area is useful, such as in catalysts or sunscreen.

AlloyMade fromProperties and uses
steeliron with a little carbonharder and stronger than pure iron
brasscopper and zincharder than copper; used for musical instruments and taps
bronzecopper and tinhard and strong; used for statues and medals
aluminium alloysaluminium with small amounts of other metalslight and strong; used for aircraft and cans
Materials and their uses

Key ideas

  • Choose a material by matching its properties to the job.
  • Copper: good conductor, malleable, used for wires.
  • Aluminium alloy: light and strong, used for aircraft and cans.
  • Nanoparticles: large surface area, used for catalysts and sunscreen.
Worked example 6.5.1
Which metal is best for an electric cable? Write the name.

Method. Think about which property the cable needs.

  1. Property. A cable must conduct electricity well and be ductile.
    conduct and ductile
  2. Choose. Copper conducts well and can be drawn into wire.
    copper
  3. Write the answer.
    copper

Check. Copper is used in most household wiring. ✓

Worked example 6.5.2
Why is an aluminium alloy used for aircraft rather than pure iron? Write one reason.

Method. Compare the properties.

  1. Compare. Aluminium alloys are light; iron is much heavier.
    light
  2. Conclude. A light, strong material saves fuel in an aircraft.
    light and strong
  3. Write the answer.
    the alloy is light and strong

Check. The alloy is also strong enough for the job. ✓

Worked example 6.5.3
Which metal is used for a jewellery ring that must not tarnish? Write the name.

Method. Match the property to the job.

  1. Property. The ring must be unreactive, so it does not tarnish.
    unreactive
  2. Choose. Gold is unreactive and does not tarnish.
    gold
  3. Write the answer.
    gold

Check. Gold is often alloyed to make it harder. ✓

Watch out

Watch out: choose a material for all the properties the job needs, not just one. A material that conducts well may not be strong enough.

Exam tip

Exam tip. Use the pattern: the job needs property X; material Y has property X; so Y is suitable.

Exercise 6E  Choosing metals, alloys and nanoparticles

1
FWhich metal is used for electrical wires? Write the name.
2
FWhich alloy is used for aircraft because it is light and strong? Write the name.
3
FWhich metal is used in jewellery because it does not tarnish? Write the name.
4
FWhat is nanoparticles’ main property used in sunscreen? Write the word. Accept absorbing UV light.
5
PSWhich material is a good choice for a statue: bronze or pure copper? Write the name.
6
PSA material must conduct electricity and be malleable for a wire. Which is better: pure copper or brass? Write the name, with a reason in one sentence.
7
RExplain why a catalyst is often made of nanoparticles, in one sentence. Accept any sentence that says the large surface area gives more active sites for reactions.
8
RExplain why both copper and brass could be used for a tap, but brass is often chosen. Accept any answer that says brass is harder and resists wear better than copper.

Chapter summary

SkillMethod
Metallic bondingPositive ions in a lattice, attracted to a sea of delocalised electrons.
Properties of metalsConduct; malleable; high melting points; shiny. Explained by the lattice and the electrons.
AlloysMixtures of metals with other elements; different-sized atoms distort the layers, so alloys are harder.
NanoparticlesBetween about 1 and 100 nm; used in sunscreens, catalysts and medicine; risks still being studied.
[H] Surface areaSmaller pieces of the same volume have more surface area; this makes nanoparticles effective catalysts.

Can you…?

  • I can describe metallic bonding and explain the properties of metals
  • I can explain why alloys are harder than pure metals, and name examples
  • I can give the size range of nanoparticles, and some uses and risks
  • I can choose a material for a purpose by matching its properties
  • [H] I can calculate surface areas and explain the surface area effect

Key terms

metallic bond
the attraction between positive metal ions and the delocalised electrons
delocalised electron
an electron that is free to move through the structure of a metal
malleable
able to be bent or hammered into shape without breaking
alloy
a mixture of a metal with another element, usually a metal
nanoparticle
a particle between about 1 and 100 nanometres across
surface area to volume ratio
[H] the surface area of a shape divided by its volume
catalyst
a substance that speeds up a reaction and is not used up

Exercise 6Z  Check-up

1
What are the delocalised particles in a metal called? Write the words.
2
What is an alloy? Write the words.
3
Name the alloy of iron and carbon. Write the name.
4
What is the size range of nanoparticles, in nanometres? Write the range.
5
Why are metals good conductors of electricity? Write the words.
6
Name the metal alloyed with copper to make bronze. Write the name.
7
Name a use of nanoparticles of gold, iron or platinum. Write the use.
8
Explain why alloys are harder than pure metals, in one sentence. Accept any sentence that says different-sized atoms distort the layers so they cannot slide.
9
[H] A cube of side 1 cm is cut into 1000 cubes of side 1 mm. How many times more surface area do they have in total? Write the number.
10
Explain why a metal is shiny, in one sentence. Accept any sentence that says the delocalised electrons reflect light.

Total 23 marks. Allow about 23 minutes.

Exercise 6X  Exam-style questions

1
FDescribe metallic bonding, in one or two sentences. Accept any answer that says positive ions are held in a sea of delocalised electrons.[2 marks]
2
RExplain why alloys are harder than pure metals. Write one or two sentences. Accept any answer that says different-sized atoms distort the layers, so the layers cannot slide.[3 marks]
3
FGive the size range of nanoparticles, in nanometres. Write the range.[1 mark]
4
FName one alloy of copper and say what it is used for. Accept brass for musical instruments or taps, or bronze for statues.[2 marks]
5
RExplain why metals are malleable, in one or two sentences. Accept any answer that says the layers of ions can slide over each other while the metallic bonds hold.[3 marks]
6
PS[H] A 2 cm cube is cut into 8 cubes of side 1 cm. Find the total surface area of the 8 cubes, in cm2. Write the number.[3 marks]
7
R[H] Explain, in one sentence, why nanoparticles make a good catalyst. Accept any sentence that says the large surface area gives more places for the reaction to happen.[2 marks]
8
RGive one benefit and one risk of nanoparticles. Accept any benefit such as sunscreen or medicine, and any risk such as effects not yet known.[3 marks]
9
PSChoose a material for an electric cable, and give one reason. Accept copper, because it conducts electricity well and can be drawn into wire.[2 marks]
10
RExplain why a pure gold ring is often made as an alloy, in one sentence. Accept any sentence that says the alloy is harder and more durable than pure gold.[2 marks]
← Chapter 5: Covalent bonding, simple and giant structuresChapter 7: Relative formula mass and conservation of mass →

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