Chemical bonds - The Sutton Academy

Revision Pack Topic 2 – Bonding, structure, and the properties of matter - Chemistry

Topic R/A/GChemical bonds Bonds occur in Chemistry because atoms and ions want to gain a full outer shell of electrons. They do this by the loss, gain or sharing of electrons

There are three types of chemical bonds; ionic, covalent and metallic Ionic bonding contains oppositely charged ions; a metal ion and a non-metal ion e.g. NaCl

Ions are atoms that have lost or gained electrons Covalent bonds occur between two non-metal atoms e.g. Carbon and hydrogen in CH4

Non-metal atoms can be found on the right hand side of the periodic table A covalent bond is a shared pair of electrons Metallic bonding contains positively charged metal ions (cations) surrounded by a ‘sea’ of delocalised electrons which are shared between the metal ions

Metallic bonding occurs in metallic elements such as iron, copper. Metallic elements can be found on the left hand side of the periodic table and in the central ‘transition metal’ block

Ionic bonding When a metal atom reacts with a non-metal atom, electrons in the outer shell of the metal atom are transferred. Metal atoms lose electrons to become positively charged ions. Non-metal atoms gain electrons to become negatively charged ions.

An atom from group one (alkali metal) will lose one electron from the outer-shell (the shell furthest from the nucleus. It does this as there is a full shell of eight electrons below. It will then have the electronic structure of a noble gas (group 0). It is easier to lose one electron than it is to gain seven to achieve a full outer shell.

The ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 have the electronic structure of a noble gas (Group 0).

An atom from group seven (halogen) will gain one electron from the outer-shell (the shell furthest from the nucleus. It does this as there is a full shell of eight electrons. It will then have the electronic structure of a noble gas (group 0). It is easier to gain one electron than lose seven.

The electron transfer during the formation of an ionic compound can be represented by a dot and cross diagram, e.g. for sodium chloride:


The bonding between two atoms in ionic bonding can be represented by drawing dot and cross diagrams for ionic compounds formed by metals in Groups 1 and 2 with non-metals in Groups 6 and 7

The charge on the ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 relates to the group number of the element in the periodic table. E.g.

Na (group one) will become Na+ Mg (group two) becomes Mg2+ Chlorine (group 7) becomes Cl- (chloride) Group 0 elements (noble gases) do not bonding in any way as they

have a full outer shell of electrons

Ionic compounds An ionic compound is a giant structure of ions. Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions. These forces act in all directions in the lattice and this is called ionic bonding.

An ionic lattice is a fixed, regular structure of oppositely charged ions The structure of sodium chloride can be represented in the following forms:

Properties of ionic compounds Ionic compounds have regular structures (giant ionic lattices) in which there are strong electrostatic forces of attraction in all directions between oppositely charged ions. These compounds have high melting points and high boiling points because of the large amounts of energy needed to break the many strong bonds.

When solid, ionic lattices do not conduct electricity as there are no free (mobile) ions to conduct electricity

When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move and so charge can flow.

Covalent bonding When atoms share pairs of electrons, they form covalent bonds. These bonds between atoms are strong. Covalently bonded substances may consist of small molecules (usually gases) such as carbon dioxide CO2 nitrogen N2 and water H2O

Revision Pack Topic 2 – Bonding, structure, and the properties of matter - Chemistry Properties of small molecules Substances that consist of small molecules are usually gases or liquids that have relatively low melting points and boiling points. These substances have only weak forces between the molecules (intermolecular forces). It is these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils.

The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points e.g. longer hydrocarbon chains

These substances do not conduct electricity because the molecules do not have an overall electric charge. Intermolecular forces are weak compared with covalent bonds and this is why it is hard to break internal covalent bonds (intramolecular) but easy to separate individual molecules (intermolecular)

Polymers Some covalently bonded substances have very large molecules, such as polymers (e.g. polythene). A polymer is a long chain molecule made from monomers; small units which are the building blocks of polymer molecules.

Polymers have very large molecules. The atoms in the polymer molecules are linked to other atoms by strong covalent bonds. The intermolecular forces between polymer molecules are relatively strong and so these substances are solids at room temperature. Students should be able to recognise polymers from diagrams showing their bonding and structure.

Representing covalent bonding Some covalently bonded substances have giant covalent structures, such as diamond and silicon dioxide. The covalent bonds in molecules and giant structures can be represented in the following forms:


Covalent structures can be represented by drawing dot and cross diagrams – you should be able to this for molecules of:

Hydrogen (H2), chlorine (Cl2), oxygen (O2), nitrogen (N2), hydrogen chloride (HCl), water (H2O), ammonia (NH3) and methane (CH4)

Know that covalent bonds in small molecules, in the repeating units of polymers and in part of giant covalent structures, are represented using a line to represent a single bond You should also be able to: • describe the limitations of using dot and cross, ball and stick, two and three-dimensional diagrams to represent molecules or giant structures • deduce the molecular formula of a substance from a given model or diagram in these forms showing the atoms and bonds in the molecule

Structure and bonding in carbon Giant covalent structures; diamond, graphite, graphene/fullerenes and silicon dioxide (silica)

Substances that consist of giant covalent structures are solids with very high melting points. All of the atoms in these structures are linked to other atoms by strong covalent bonds. These bonds must be overcome to melt or boil these substances. Diamond and graphite (forms of carbon) and silicon dioxide (silica) are examples of giant covalent structures. You should be able to recognise giant covalent structures from diagrams showing their bonding and structure.

In diamond, each carbon atom forms four covalent bonds with other carbon atoms in a giant covalent structure, so diamond is very hard, has a very high melting point and does not conduct electricity

Properties of giant covalent compounds You should be able to explain the properties of diamond in terms of its structure and bonding.

In graphite, each carbon atom forms three covalent bonds with three other carbon atoms, forming layers of hexagonal rings which have no covalent


bonds between the layers. In graphite, one electron from each carbon atom is delocalised. You should be able to explain the properties of graphite in terms of its structure and bonding. You should know that graphite is similar to metals in that it has delocalised electrons and can conduct electricity Graphene is a single layer of graphite and has properties that make it useful in electronics and composites. You should be able to explain the properties of graphene in terms of its structure and bonding.

Fullerenes are molecules of carbon atoms with hollow shapes. The structure of fullerenes is based on hexagonal rings of carbon atoms but they may also contain rings with five or seven carbon atoms. The first fullerene to be discovered was Buckminsterfullerene (C60) which has a spherical shape.

Carbon nanotubes are cylindrical fullerenes with very high length to diameter ratios. Their properties make them useful for nanotechnology, electronics and materials. You should be able to: • recognise graphene and fullerenes from diagrams and descriptions of their bonding and structure • give examples of the uses of fullerenes, including carbon nanotubes.

Metallic bonding Metals consist of giant structures of atoms arranged in a regular pattern. The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure. The sharing of delocalised electrons gives rise to strong metallic bonds

The bonding in metals may be represented in the following form:

Properties of metals and alloys Metals have giant structures of atoms with strong metallic bonding. This means that most metals have high melting and boiling points. In pure metals, atoms are arranged in layers, which allows metals to be bent and shaped. Pure metals are too soft for many uses and so are mixed with other metals to make alloys which are harder.

Alloys are harder than pure metals because of distortion in the layers of atoms in the structure of a pure metal

Metals are good conductors of electricity because the delocalised electrons in the metal carry electrical charge through the metal. Metals are good


conductors of thermal energy because energy is transferred by the delocalised electrons. The three states of matter The three states of matter are solid, liquid and gas. Melting and freezing take place at the melting point, boiling and condensing take place at the boiling point. The three states of matter can be represented by a simple model. In this model, particles are represented by small solid spheres. Particle theory can help to explain melting, boiling, freezing and condensing.

The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles of the substance. The nature of the particles involved depends on the type of bonding and the structure of the substance. The stronger the forces between the particles the higher the melting point and boiling point of the substance.

(HT only) Limitations of the simple model above include that in the model there are no forces, that all particles are represented as spheres and that the spheres are solid.

You should be able to: • predict the states of substances at different temperatures given appropriate data • explain the different temperatures at which changes of state occur in terms of energy transfers and types of bonding • recognise that atoms themselves do not have the bulk properties of materials • (HT only) explain the limitations of the particle theory in relation to changes of state when particles are represented by solid inelastic spheres which have no forces between them.

State symbols In chemical equations, the three states of matter are shown as (s), (l) and (g), with (aq) for aqueous solutions. You should be able to include appropriate state symbols in chemical equations for the reactions in this specification.

Sizes of particles and their properties Nanoscience refers to structures that are 1–100 nm in size, of the order of a few hundred atoms.

Nanoparticles, are smaller than fine particles (PM2.5), which have diameters between 100 and 2500 nm (1 x 10-7 m and 2.5 x 10-6 m).


Coarse particles (PM10) have diameters between 1 x 10-5 m and 2.5 x 10-6 m. Coarse particles are often referred to as dust. As the side of cube decreases by a factor of 10 the surface area to volume ratio increases by a factor of 10.

Nanoparticles may have properties different from those for the same materials in bulk because of their high surface area to volume ratio. It may also mean that smaller quantities are needed to be effective than for materials with normal particle sizes

Uses of nanoparticles Nanoparticles have many applications in medicine, in electronics, in cosmetics and sun creams, as deodorants, and as catalysts. New applications for nanoparticulate materials are an important area of research. There are are advantages and disadvantages of the applications of these nanoparticulate materials, but you do not need to know specific examples or properties other than those specified.

You should be able to: • given appropriate information, evaluate the use of nanoparticles for a specified purpose • explain that there are possible risks associated with the use of nanoparticles

Revision Pack Topic 2 – Bonding, structure, and the properties of matter - Chemistry Formation of ions and Ionic Bonding:

1. Define ion:

2. Describe how an ion differs to an atom of the same element:

3. Explain how an atom of sodium (Na) becomes an ion of sodium (Na+). You may used an electron shell diagram to help you:

4. Describe why an atom loses or gains electrons:

5. Define Ionic Bonding:

Revision Pack Topic 2 – Bonding, structure, and the properties of matter - Chemistry What Ions will the following elements form?

1. Potassium: 2. Sodium: 3. Chlorine: 4. Magnesium: 5. Oxygen: 6. Describe the relationship between the ions in 1-5 and the group that each of

the atoms in found in:

Drawing ionic bonding diagrams: For each of the following examples:

1. Identify the elements involved in the compound 2. State the ions formed by each element 3. Draw electron shell diagrams for each of the elements involved 4. Name the compound formed and state its formula

Example: Sodium and chlorine

1. Sodium and chlorine 2. Na+ and Cl- (group one and group seven elements) 3. Sodium loses one electron and transfers the electron to chlorine 4. The compound is named sodium chloride - NaCl

Revision Pack Topic 2 – Bonding, structure, and the properties of matter - Chemistry Potassium and chlorine

Potassium bromide

Calcium and Oxygen:

Magnesium and Sulfur:

Revision Pack Topic 2 – Bonding, structure, and the properties of matter - Chemistry Harder: Sodium and Sulfur (Note: Sulfur goes in the middle and the formula is Na2S)

Ionic Structures (Compounds):



Exam question practice – ions, ionic bonding and ionic lattices







Answers to exam questions – ions, ionic bonding and ionic lattices




Comparing different types of bonding Summary: A look at comparing ionic, covalent and metallic bonding

Molecular structure - ________________

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OR Giant structure - ________________

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Ionic bond - ______________________

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Covalent bond - _________________________

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Metallic bond - _________________________

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Ionic Compounds

Simple molecular covalent

Giant molecular covalent

Metallic structures

Drawing of the structure

Description of the structure

Type of atoms?

Melting and Boiling Points?

Conductivity?


Diamond Graphite Structure: Structure:

Properties: Properties:

Why does it have these properties?

Why does it have these properties?

Comparison:


Covalent bonding High melting & boiling points e.g.

diamond & graphite

Simple molecular Located on the right‐side of the

periodic table

Giant Molecular The sharing of electrons

Non metals Made up of only one type of atom

Compound Low melting & boiling points

Element Two or more different types of

atom chemically bonded together What is meant by a covalent bond? ______________________________________________________________________________________________________________________________________________________________________________________________ Draw a covalent bond for the following (just show the outer electrons): Hydrogen Chloride HCl Hydrogen H2 Methane CH4 Water H2O Carbon dioxide, CO2 Properties of covalent substances:

Revision Pack Topic 2 – Bonding, structure, and the properties of matter - Chemistry The above structures are all examples of ______________ molecular compounds. They have ________ melting and boiling points and they do not _______________ electricity. Explain why the simple covalent have low melting and boiling points ______________________________________________________________________________________________________________________________________________________________________________________________ Diamond and graphite are both ___________ covalent substances: Label the diagrams below:

________________________________ ________________________________ Explain why giant covalent compounds have a high melting and boiling point: _____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Explain why graphite can conduct electricity but diamond cannot: ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Explain why graphite can act as a lubricant:

_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________


Metallic bonding: Complete the labelling: Why do the metals form positive ions? ______________________________________________________________________________________________________________________________________________________________________________________________ Explain why metals can conduct electricity. ______________________________________________________________________________________________________________________________________________________________________________________________ Explain why metals are malleable (can be hit into shape). ______________________________________________________________________________________________________________________________________________________________________________________________ Most metals are found in the middle part of the period table, they are called ___________________ metals. Transition metals have _____________melting points and form ______________ compounds.


Questions Q1. Complete the sentence by putting a cross ( ) in the box next to your answer. Carbon dioxide is a gas at room temperature. A carbon dioxide molecule is a

(1) A giant molecule that has covalent bonds B giant molecule that has ionic bonds C simple molecule that has covalent bonds D simple molecule that has ionic bonds

Q2.

The table shows some properties of six compounds.

compound melting point / °C

boiling point / °C

solubility in water

electrical conductivity of solution

copper sulfate 200 decomposes soluble high

hexane –95 69 insoluble does not dissolve

hydrogen chloride

–112 –85 soluble high

octane –57 126 insoluble does not dissolve

silicon(IV) oxide

1610 2230 insoluble does not dissolve

sodium chloride

801 1413 soluble high

(a) Which of the following lists of compounds from the table contains only ionic compounds? Put a cross ( ) iin the box next to your answer.

(1) A copper sulfate, octane and sodium chloride B silicon(IV) oxide and sodium chloride C copper sulfate and sodium chloride D copper sulfate and silicon(IV) oxide


(b) Two of the compounds in the table produce a colour in a flame test. Give the name of one of these compounds and the colour it produces in the flame test.

(2)

compound . . . . . . . . . . . . . . . . . . . .

colour . . . . . . . . . . . . . . . . . . . .

(c) Hexane is a covalent compound containing simple molecules. It has a low boiling point. (i) Explain why it has a low boiling point.

(2) (d) Draw a dot and cross diagram of a molecule of hydrogen chloride. Show outer electrons only.

(2)

(Total for Question is 9 marks)

Revision Pack Topic 2 – Bonding, structure, and the properties of matter - Chemistry Q3. Structures

The table shows some properties of diamond and graphite.

diamond graphite

colourless crystals black, shiny solid very hard flakes easily does not conduct electricity conducts electricity

(i) Suggest why diamond and graphite might be expected to have similar properties.

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(ii) By referring to its structure, explain why diamond is very hard. (3)

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(iii) By referring to its structure, explain why graphite flakes easily. (2)

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Q4. The atomic number of carbon is 6 and of fluorine is 9. Carbon and fluorine atoms are combined in a tetrafluoromethane molecule, CF4. Draw a dot and cross diagram of a tetrafluoromethane molecule. Show outer electrons only.

(2)

Q5. Metals

There are many metallic elements in the periodic table.

(a) Which row of the table correctly shows two metals that are in group 1 and two metals that are transition metals? Put a cross ( ) in the box next to your answer.

(1)

(b) (i) Describe the structure of metals in terms of the particles present in their structures.

(2)

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(ii) Explain how metals conduct electricity.

(2)

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(c) (i) Describe what you would see when a small piece of sodium is added to water.

(2)

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(ii) Write the balanced equation for the reaction of sodium with water to form sodium hydroxide and hydrogen.

(3)

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(Total for question = 10 marks)


Comparing different types of bonding – answers Q1.

Question Number

Answer Acceptable answers

Mark

C (1) Q2.

Answer Acceptable

answers Mark

(a) C : copper sulfate and sodium chloride

(1)

(b) copper sulfate (1) blue-green (1) or sodium chloride (1) yellow (1) colour mark consequential on correct metal (compound)

allow blue or green or green-blue reject orange and yellow-orange

(2)

(c)(i) An explanation linking weak intermolecular forces /weak forces between molecules (1) little heat / energy needed to separate (molecules) (1)

bonds / attractions in place of forces intermolecular forces between atoms / bonds loses 1st marking point any answer in terms of covalent or ionic bonding scores zero

(2)

(c)(ii) A description linking use separating funnel (1) run off lower layer / liquid / OWTTE (1)

alternative description of separating funnel eg funnel with a tap at the bottom suitable labelled diagram burette allow layers / liquids to separate ignore fractional

(2)


distillation (d)

shared pair in molecule (1) rest of molecule consequent on first mark (1)

Allow a diagram without labels for 2 marks any symbols shown must be correct for the 2nd mark allow any combination of dots and crosses for electrons wrong compound = zero marks

(2)

Q3.

Question Number


Mark

(i) both (pure forms of) carbon / both giant molecular

(1) Question Number


Mark

(ii) An explanation linking three of the following points • (every) carbon atom forms four bonds (1) • strong bonds / hard to separate atoms from lattice (1) • covalent bonds (1) • no weaknesses in molecule (1)

(3) Question Number


Mark

(iii) An explanation linking the following • (in) layers (1) • weak forces between layers (1)

(2)


Question Number


Mark

• four bonding pairs shown (1) • six non bonded electrons on each fluorine atom (1)

(2)




Extended response questions on bonding

Question:





Answers to extended questions





Nanoparticles and nanomaterials exam questions

Q1.The figure below shows magnesium burning in air.

© Charles D Winters/Science Photo Library

(a) Look at the figure above.

How can you tell that a chemical reaction is taking place?

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(b) Name the product from the reaction of magnesium in the figure.

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(c) The magnesium needed heating before it would react.

What conclusion can you draw from this?

Tick one box.

The reaction is reversible

The reaction has a high activation energy

The reaction is exothermic

Magnesium has a high melting point

(1)

(d) A sample of the product from the reaction in the figure above was added to water and shaken.

Universal indicator was added.

The universal indicator turned blue.

What is the pH value of the solution?

Tick one box.

1

4

7

9

(1)


(e) Why are nanoparticles effective in very small quantities?

Tick one box.

They are elements

They are highly reactive

They have a low melting point

They have a high surface area to volume ratio

(1)

(f) Give one advantage of using nanoparticles in sun creams.

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(g) Give one disadvantage of using nanoparticles in sun creams.

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(h) A coarse particle has a diameter of 1 × 10−6 m.


A nanoparticle has a diameter of 1.6 × 10−9 m.

Calculate how many times bigger the diameter of the coarse particle is than the diameter of the nanoparticle.

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(Total 9 marks)

Q2.The article gives some information about graphene.

Nanotunes!


Carbon can be made into nano-thin, strong sheets called graphene. A graphene sheet is a single layer of graphite. Graphene conducts electricity and is used in loudspeakers. The picture shows the structure of graphene.

© 7immy/iStock

(a) Use the picture and your knowledge of bonding in graphite to:

(i) explain why graphene is strong;

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(ii) explain why graphene can conduct electricity.

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(b) Graphite is made up of layers of graphene.

Explain why graphite is a lubricant.

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(Total 7 marks) Q3.This question is about atoms, molecules and nanoparticles.

(a) Different atoms have different numbers of sub-atomic particles.


(i) An oxygen atom can be represented as O

Explain why the mass number of this atom is 16.

You should refer to the numbers of sub-atomic particles in the nucleus of the atom.

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(ii) Explain why C and C are isotopes of carbon.

You should refer to the numbers of sub-atomic particles in the nucleus of each isotope.

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(b) Hydrogen atoms and oxygen atoms chemically combine to produce water molecules.

(i) Complete the figure below to show the arrangement of the outer shell electrons of the hydrogen and oxygen atoms in a molecule of water.


Use dots (•) or crosses (×) to represent the electrons.

(2)

(ii) Name the type of bonding in a molecule of water.

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(iii) Why does pure water not conduct electricity?

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(c) Nanoparticles of cobalt oxide can be used as catalysts in the production of hydrogen from water.

(i) How does the size of a nanoparticle compare with the size of an atom?

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(ii) Suggest one reason why 1 g of cobalt oxide nanoparticles is a better catalyst than 1g of cobalt oxide powder.

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(Total 11 marks)

Q4.Magnesium oxide nanoparticles can kill bacteria.

The figure below shows the percentage of bacteria killed by different sized nanoparticles.

Size of nanoparticles in nanometres

(a) (i) Give two conclusions that can be made from the figure above.

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(ii) Points are plotted for only some sizes of nanoparticles.

Would collecting and plotting data for more sizes of nanoparticles improve the conclusions?


Give a reason for your answer.

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(b) Magnesium oxide contains magnesium ions (Mg2+) and oxide ions (O2–).

Describe, as fully as you can, what happens when magnesium atoms react with oxygen atoms to produce magnesium oxide.

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(Total 7 marks)

Q5. The picture shows a copper kettle being heated on a camping stove.

Copper is a good material for making a kettle because:

• it has a high melting point


• it is a very good conductor of heat.

(a) Explain why copper, like many other metals, has a high melting point. You should describe the structure and bonding of a metal in your answer.

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(b) An aeroplane contains many miles of electrical wiring made from copper. This adds to the mass of the aeroplane.

It has been suggested that the electrical wiring made from copper could be replaced by lighter carbon nanotubes.


The diagram shows the structure of a carbon nanotube.

(i) What does the term ‘nano’ tell you about the carbon nanotubes?

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(ii) Like graphite, each carbon atom is joined to three other carbon atoms.

Explain why the carbon nanotube can conduct electricity.

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(Total 7 marks)

Nanoparticles and nanomaterials exam question answers

M1.(a) any one from:


• there was a flame • energy was given out • a new substance was formed • the magnesium turned into a (white) powder

answers must be from the figure 1

(b) Magnesium oxide 1

(c) The reaction has a high activation energy 1

(d) 9 1

(e) They have a high surface area to volume ratio 1

(f) any one from:

• Better coverage • More protection from the Sun’s ultraviolet rays

1

(g) any one from:

• Potential cell damage to the body • Harmful effects on the environment

1

(h) indication of = 0.625 and use of indices 10−9 − 10−6 = 103


Both steps must be seen to score first mark 1

0.625 × 1000 = 625 (times bigger) 1

[9]

M2.(a) (i) giant lattice

allow each carbon atom is joined to three others 1

atoms in graphene are covalently bonded

max. 2 marks if any reference to wrong type of bonding 1

and covalent bonds are strong or need a lot of energy to be broken

allow difficult to break 1

(ii) because graphene has delocalised electrons

allow each carbon atom has one free electron 1

which can move throughout the structure

do not accept just electrons can move. 1

(b) because there are weak forces between molecules

allow no bonds between the layers 1


so layers / molecules can slip / slide. 1

[7]

(a) (i) (mass number = 16) because there are 8 protons and 8 neutrons (in the nucleus)

accept mass number is total number of protons and neutrons for 1 mark

2

(ii) same number of protons or both have 6 protons

accept same atomic number 1

12C has 6 neutrons 1

14C has 8 neutrons 1

accept different number of neutrons for 1 mark

numbers, if given, must be correct

incorrect reference to electrons = max 2 marks

(b) (i) 2 bonding pairs 1

additional unbonded electrons negates this mark

4 unbonded electrons around oxygen 1

accept dot, cross or e or – or any combination

(ii) covalent 1

(iii) any one from:


• no delocalised / free electrons ignore mobile electrons

• no overall electric charge accept no charge (carriers)

• no ions 1

do not accept any implications of the presence of ions

(c) (i) larger

accept the size of a few hundred atoms

accept atoms are smaller (than nanoparticles)

allow up to 1000 atoms) 1

(ii) (nanoparticles have) large(r) surface area 1

[11]

(a) (i) any two from:

ignore any conclusion drawn referring to data below 7.5 nm or above 20 nm

• 100% of (type 1 and type 2) bacteria are killed with a particle size of 7.5 to 8.5 nm

accept nanoparticles in the range of 7.5 to 8.5 nm are most effective at killing (type 1 and type 2) bacteria

• as the size increases (beyond 8.5 nm), nanoparticles are less effective at killing (type 1 and type 2) bacteria

• type 1 shows a linear relationship or type 2 is non-linear • type 1 bacteria more susceptible than type 2 (at all sizes of nanoparticles

shown on the graph)

allow type 2 bacteria are harder to kill 2

(ii) (yes) because you could confirm the pattern that has been observed

allow would reduce the effect of anomalous points / random errors

allow would give better line of best fit

ignore references to reliability / precision / accuracy / reproducibility / repeatability / validity

or


(no) because trend / conclusion is already clear 1

(b) magnesium loses electron(s) 1

oxygen gains electron(s) 1

two electrons (per atom) 1

gives full outer shells (of electrons) or eight electrons in highest energy level

reference to incorrect particles or incorrect bonding or incorrect structure = max 3

1

or

(electrostatic) attraction between ions or forms ionic bonds

accept noble gas structure [7]

M5. (a) any four from:

max 3 marks if any reference made to covalent / ionic bonding / molecules or intermolecular forces or graphite / diamond or forces of attraction between electrons and then ignore throughout

• giant structure / lattice

ignore layers

• positive ions

• sea of electrons or delocalised / free electrons

ignore electrons can move

• awareness of outer shell / highest energy level electrons are involved

• (electrostatic) attractions / bonds between electrons and positive ions

• bonds / attractions (between atoms/ ions) are strong

allow hard to break for strong

ignore forces unqualified

• a lot of energy / heat is needed to break these bonds / attractions

ignore high temperature


4

(b) (i) that they are very small

accept tiny / really small / a lot smaller / any indication of very small

eg microscopic, smaller than the eye can see

or

1–100 nanometres or a few (hundred) atoms

ignore incorrect numerical values if very small is given 1

(ii) any 2 from:

• one (non-bonded) electron from each atom

• delocalised / free electrons

allow sea of electrons

ignore electrons can move

• electron carry / form / pass current / charge

ignore carry electricity 2

[7]

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Chemical bonds - The Sutton Academy

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