Skip to content
Cambridge IGCSE0620

Elements, compounds and mixtures

Chemistry 0620 Chapter Notes

What this chapter covers

Elements, compounds and mixturesAtomic structure and the Periodic TableIsotopesIons and ionic bondsSimple molecules and covalent bondsGiant covalent structuresMetallic bonding
ShareWhatsAppPost
Elements, compounds and mixtures notes

Read online free. Download a watermarked copy with a free account.

Read the notes

The full Elements, compounds and mixtures notes as text: skim, search, and jump between subtopics.

~43 min read

In this chapter

  1. 1Elements: one sort of atom
  2. 2Compounds: elements chemically combined
  3. 3Mixtures: not chemically combined
  4. 4Telling the three apart
  5. 5Protons, neutrons and electrons
  6. 6Proton number and nucleon number
  7. 7Counting particles in atoms and ions
  8. 8Electronic configuration
  9. 9Groups, periods and noble gases
  10. 10What isotopes are
  11. 11Reading the symbol of an atom or ion
  12. 12Why isotopes behave alike
  13. 13Relative atomic mass from isotopes
  14. 14Cations and anions
  15. 15The ionic bond
  16. 16Ionic bonds from Group I and Group VII
  17. 17Properties of ionic compounds
  18. 18The giant ionic lattice
  19. 19Ionic bonds from metals and non-metals
  20. 20Explaining the properties of ionic compounds
  21. 21The covalent bond
  22. 22Simple molecules: H₂, Cl₂, H₂O, CH₄, NH₃, HCl
  23. 23Properties of simple molecular compounds
  24. 24Double and triple bonds: O₂, CO₂, N₂, C₂H₄, CH₃OH
  25. 25Why the properties follow from the structure
  26. 26Diamond and cutting tools
  27. 27Graphite: layers and lubricant
  28. 28Graphite as an electrode
  29. 29Silicon(IV) oxide
  30. 30Diamond and silicon(IV) oxide compared
  31. 31What metallic bonding is
  32. 32Which particles are in the lattice
  33. 33Electrical conductivity
  34. 34Malleability and ductility

1. Elements: one sort of atom

An element is a substance made of only one sort of atom. Nitrogen, oxygen, chlorine, copper and sulfur are elements.

Elements can be metallic, like copper, or non-metallic, like sulfur. A particle of an element can hold more than one atom, so long as every atom is the same sort. N₂ and Cl₂ are elements, because every atom in each is the same sort.

Examiner insight

“Better performing candidates wrote about substance containing only one sort of atom.” “The most common error was to suggest F (sulfur trioxide), which is a compound, not an element.”

Worked example 11 mark

The table shows some physical properties of four different substances.

Which row describes the properties of a non-metallic element?

melting point / °Cconductivity when solidconductivity when melted
A63goodgood
B119poorpoor
C659goodgood
D808poorgood
  1. 1

    B: 119 °C, poor conductivity when solid and poor when melted. [1]

2. Compounds: elements chemically combined

A compound contains two or more elements chemically combined. Water is a compound of hydrogen and oxygen. Carbon dioxide, CO₂, and potassium bromide are compounds too.

The elements in a compound can only be separated using a chemical change. Ethanol is a pure compound.

Examiner insight

“Many candidates did not mention that hydrocarbons are compounds. This is an important word to include since ‘it contains hydrogen and carbon’ could refer to a mixture of hydrogen and carbon.”

Worked example 11 mark

Which statement describes a compound?

A It contains two or more elements chemically combined. · B It contains two or more elements physically combined. · C It contains two or more elements forming an alloy. · D It contains two or more elements that can easily be separated.

  1. 1

    A: two or more elements chemically combined. [1]

3. Mixtures: not chemically combined

A mixture contains two or more substances that are not chemically combined. Brass, aqueous sodium chloride, air and petroleum are mixtures.

Brass is an alloy, and an alloy is a mixture, not a compound. Copper and zinc in brass are both elements, but they are not chemically combined.

Examiner insight

“A number of candidates wrongly selected B, thinking that brass (an alloy) is a compound.”

Worked example 11 mark

Which row about elements, mixtures and compounds is correct?

metallic elementnon-metallic elementmixturecompound
Acoppermethanebrasssulfur
Bbrasssulfurcoppermethane
Ccoppersulfurbrassmethane
Dbrassmethanecoppersulfur
  1. 1

    C: copper is a metallic element, sulfur a non-metallic element, brass a mixture, methane a compound. [1]

4. Telling the three apart

Ask two questions. Does it hold only one sort of atom? Then it is an element. Does it hold two or more elements? Then ask whether they are chemically combined. If yes, it is a compound. If no, it is a mixture.

A formula helps. KCl has two different elements, so it is a compound. Cl₂ has two atoms but one element, so it is an element. A name that starts with ‘aqueous’ is a solution, and a solution is a mixture.

Worked example 11 mark

Which row identifies an element, a compound and a mixture?

elementcompoundmixture
Aaqueous sodium chloridepotassium iodidecopper
Bironpotassium bromideaqueous sodium nitrate
Cpotassium bromideironaqueous sodium chloride
Dcopperaqueous sodium nitratepotassium iodide
  1. 1

    B: iron is an element, potassium bromide a compound, aqueous sodium nitrate a mixture. [1]

Recap

  • Element: only one sort of atom. N₂ and Cl₂ are elements.
  • Compound: two or more elements chemically combined.
  • Elements in a compound can only be separated using a chemical change.
  • Mixture: two or more substances not chemically combined.
  • An alloy such as brass is a mixture, never a compound.
  • Different elements in a formula means a compound, as in KCl and CO₂.

5. Protons, neutrons and electrons

An atom has a central nucleus containing neutrons and protons, surrounded by electrons in shells.

A proton has relative charge +1 and relative mass 1. A neutron has relative charge 0 and relative mass 1. An electron has relative charge −1 and a much smaller relative mass, 1/1840.

In an atom, the number of electrons is equal to the number of protons.

proton: charge +1, mass 1

neutron: charge 0, mass 1

electron: charge -1, mass 1/1840

Examiner insight

“Many candidates did not realise that it was the relative charge that was asked for; “+1”, rather than “+”, for the relative charge of a proton was expected.” “Candidates found this challenging and confused relative mass and charge of the subatomic particles – neutron and electron.”

Worked example 11 mark

Four statements about particles in an atom are listed.

1 Protons and neutrons have the same relative mass and different relative charges.

2 Protons and neutrons have different relative masses and the same relative charge.

3 Protons and electrons have the same relative mass and different relative charges.

4 Protons and electrons have different relative masses and different relative charges.

Which statements are correct?

A 1 and 3

B 1 and 4

C 2 and 3

D 2 and 4

  1. 1

    Proton: charge +1, mass 1. Neutron: charge 0, mass 1. Electron: charge -1, mass 1/1840.

  2. 2

    Statement 1 is correct: the masses are both 1 and the charges are +1 and 0.

  3. 3

    Statement 2 is wrong: the masses are the same. Statement 3 is wrong: the masses differ.

  4. 4

    Statement 4 is correct: the masses and the charges both differ.

  5. 5

    Statements 1 and 4 are correct, so the answer is B. [1]

6. Proton number and nucleon number

Proton number / atomic number is the number of protons in the nucleus of an atom. It decides which element an atom is.

Mass number / nucleon number is the total number of protons and neutrons in the nucleus of an atom.

In the symbol ^{23}_{11}Na, the top number is the nucleon number and the bottom number is the proton number.

nucleon number = protons + neutrons

Examiner insight

“The phrase “in one atom” was often missing.” “Electrons were sometimes referred to inappropriately, and a small number of candidates confused nucleons with neutrons.”

Worked example 11 mark

Which statement defines atomic number?

A It is the total number of protons in the nucleus of an atom.

B It is the total number of protons and neutrons in the nucleus of an atom.

C It is the number of different atoms in one molecule.

D It is the simplest whole number ratio of atoms in a compound.

  1. 1

    Atomic number is the number of protons in the nucleus of an atom.

  2. 2

    B describes the nucleon number, because it adds the neutrons.

  3. 3

    C and D describe a molecule and a formula, not an atom.

  4. 4

    The answer is A. [1]

7. Counting particles in atoms and ions

In an atom, the number of electrons equals the proton number. The number of neutrons is the nucleon number minus the proton number.

An ion has a charge, so its electrons and protons are unequal. A positive ion has lost electrons. A negative ion has gained electrons. Only the electrons change: the protons and neutrons stay the same.

For the ion ^{59}_{27}Co²⁺: protons = 27, neutrons = 59 - 27 = 32, electrons = 27 - 2 = 25.

neutrons = nucleon number - proton number

electrons in an ion = protons - charge

Examiner insight

“The commonest errors were to suggest 38 electrons (ignoring the charge on the ion) or 38 neutrons (by not subtracting proton number from mass number).” “A few candidates confused the number of neutrons and thought that they were the mass number of 50.”

Worked example 12 marks

Deduce the number of neutrons and protons in an atom of the isotope of titanium ^{50}_{22}Ti.

  1. 1

    protons = proton number = 22 [1]

  2. 2

    neutrons = 50 - 22 = 28 [1]

8. Electronic configuration

Fill the shells from the nucleus outwards: 2 electrons in the first shell, then up to 8 in the second, then up to 8 in the third. Potassium, with 19 electrons, starts a fourth shell: 2,8,8,1.

For an ion, first work out the number of electrons, then fill the shells. For example, aluminium is 2,8,3 but its ion Al³⁺ is 2,8.

A positive ion has fewer electrons than its atom. A negative ion has more.

Na: 2,8,1 → Na⁺: 2,8

Cl: 2,8,7 → Cl⁻: 2,8,8

Ca: 2,8,8,2 → Ca²⁺: 2,8,8

Examiner insight

“However, some candidates gave 2,8,3 which is the electronic configuration of the aluminium atom, presumably as a result of misreading the question.” “The most common error was omitting the fourth electron shell of K.”

Worked example 11 mark

Which atom or ion has the electronic configuration 2,8,8?

A Ne

B Na⁺

C Br⁻

D Ca²⁺

  1. 1

    Ne has 10 electrons: 2,8.

  2. 2

    Na⁺ has 11 - 1 = 10 electrons: 2,8.

  3. 3

    Br⁻ has 35 + 1 = 36 electrons, far too many for 2,8,8.

  4. 4

    Ca²⁺ has 20 - 2 = 18 electrons: 2,8,8. The answer is D. [1]

9. Groups, periods and noble gases

For Groups I to VII, the number of outer shell electrons equals the group number. The number of occupied electron shells equals the period number.

The Group VIII noble gases have a full outer electron shell. Neon, 2,8, and argon, 2,8,8, have eight outer electrons. Helium has two.

Mg: 2,8,2 ⇒ Group II, Period 3

Ar: 2,8,8 ⇒ full outer shell, Period 3

Examiner insight

“Candidates who wrote about ‘eight electrons in the outer shell’ did not gain credit because the question was more general; helium has two electrons in its outer shell.” “Some candidates confused the period and mainly thought that titanium was in period 3. They had forgotten that hydrogen and helium are in period 1.”

Worked example 11 mark

Which statement about the atomic structure of the named element is correct?

A Antimony, Sb, has only four occupied electron shells.

B Selenium, Se, has only six electrons in its third electron shell.

C Strontium, Sr, has four outer-shell electrons.

D Xenon, Xe, has five fully occupied electron shells.

  1. 1

    Occupied shells = period number. Outer-shell electrons = group number.

  2. 2

    A is wrong: antimony is in Period 5, so it has five occupied shells.

  3. 3

    B is wrong: selenium is in Group VI and Period 4, so its six outer electrons are in the fourth shell.

  4. 4

    C is wrong: strontium is in Group II, so it has two outer-shell electrons.

  5. 5

    D is correct: xenon is in Period 5, so it has five occupied shells, and it is a Group VIII noble gas, so its outer shell is full. The answer is D. [1]

Recap

  • Nucleus: protons (+1, mass 1) and neutrons (0, mass 1). Electrons (−1, mass 1/1840) are in shells.
  • Proton number = protons in the nucleus of an atom. Nucleon number = protons + neutrons.
  • Neutrons = nucleon number − proton number.
  • Atom: electrons = protons. Ion: electrons = protons − charge.
  • Shells fill 2, 8, 8, then a fourth shell. Write the ion's own electron count, for example Na is 2,8,1 but Na⁺ is 2,8.
  • Outer-shell electrons = group number (Groups I to VII). Occupied shells = period number.
  • Noble gases have a full outer shell: helium has two, neon and argon have eight.

10. What isotopes are

Isotopes are different atoms of the same element that have the same number of protons but different numbers of neutrons.

The key word is atoms. Isotopes are not different elements and not compounds. A full definition names both particles: protons and neutrons. Oxygen is an element that has isotopes, for example ^{16}O and ^{18}O.

Examiner insight

“An atom with the same number of protons but a different number of neutrons was required.” “Both protons and neutrons were required but a common error was to give only one of the particles.”

Worked example 12 marks

Oxygen is an element that has isotopes. State the meaning of the term isotopes.

  1. 1

    (atoms of the same element that have the) same number of protons [1]

  2. 2

    different number of neutrons [1]

11. Reading the symbol of an atom or ion

In a symbol such as ^{12}_{6}C, the top number is the nucleon number (mass number) and the bottom number is the proton number (atomic number).

The number of neutrons is the nucleon number minus the proton number. In an atom, the number of electrons is equal to the proton number.

For an ion, use the charge. In ^{35}_{17}Cl⁻ there are 17 protons, 18 neutrons and 18 electrons, because the charge of 1– means one extra electron.

Examiner insight

“However, many were unable to link the charge on the sulfide ion with the correct number of electrons, and the number was often given as 16 rather than 18.” “The commonest errors were to suggest 12 electrons and 11 neutrons or to give the mass number as the number of electrons or neutrons.”

Worked example 12 marks

Indium has an atomic number of 49. A sample of indium contains two isotopes, ^{113}In and ^{115}In.

Complete Table 2.1 to show the number of protons and the number of neutrons in one atom of each isotope of indium.

isotopenumber of protonsnumber of neutrons
^{113}In
^{115}In
  1. 1

    Number of protons: 49 and 49 [1]

  2. 2

    Number of neutrons: 113 - 49 = 64 and 115 - 49 = 66 [1]

12. Why isotopes behave alike

Isotopes of the same element have the same chemical properties.

This is because they have the same number of electrons, and therefore the same electronic configuration.

Isotopes have the same number of protons and electrons. Only the number of neutrons is different.

Examiner insight

“Candidates knew about the different number of neutrons but were unclear about the chemical properties of different isotopes.”

Worked example 11 mark

The table shows the number of protons, neutrons and electrons in four different particles.

Which two particles have the same chemical properties?

A W and X · B W and Y · C X and Z · D Y and Z

particleprotonsneutronselectrons
W171817
X161818
Y172017
Z182018
  1. 1

    B: W and Y. [1]

  2. 2

    W and Y both have 17 protons and 17 electrons, so they are isotopes of the same element.

  3. 3

    X and Z both have 18 electrons but different numbers of protons: different elements.

13. Relative atomic mass from isotopes

Relative atomic mass is the average mass of an atom of an element compared to the mass of a specific isotope, carbon-12, ^{12}C.

To calculate it, multiply each relative mass by its abundance. Add the results, then divide by the total abundance. Show every line of working.

Ar = ((m₁ × a₁) + (m₂ × a₂) + …)/(total abundance)

Examiner insight

“Many candidates had the idea that carbon was required but chose 14C or just ‘carbon’.” “The most common errors seen were: averaging of the two relative masses 32 and 34 to gain 33 without using the percentage abundances; answers of 32 seen without working out (perhaps using the mass number of sulfur given in the Periodic Table); correctly calculated answers of 32.1 that were then incorrectly rounded to a final answer of 32 or 32.0.”

Worked example 12 marks

A sample of indium contains two isotopes, ^{113}In and ^{115}In. Table 2.2 shows the relative abundances of the two isotopes in the sample of indium.

Calculate the relative atomic mass of this sample of indium to one decimal place.

isotope^{113}In^{115}In
relative abundance119
  1. 1

    (113 × 1) + (115 × 19) = 2298 [1]

  2. 2

    Total abundance = 1 + 19 = 20, so 2298 ÷ 20 = 114.9 [1]

Recap

  • Isotopes are different atoms of the same element: same number of protons, different numbers of neutrons.
  • In ^{12}_{6}C the top number is the nucleon number and the bottom number is the proton number.
  • Neutrons = nucleon number − proton number. In an atom, electrons = proton number.
  • In an ion, the charge changes the electrons: Cl⁻ has one more electron than protons.
  • Extended: isotopes have the same chemical properties because they have the same number of electrons and the same electronic configuration.
  • Extended: relative atomic mass = sum of (relative mass × abundance) ÷ total abundance.

14. Cations and anions

A positive ion is known as a cation. A negative ion is known as an anion.

A cation forms when an atom loses electrons, so the ion has fewer electrons than the atom. An anion forms when an atom gains electrons. The number of protons does not change.

Examiner insight

“Option A gave the correct description of the number of electrons in a positive ion compared to an atom but did not give the correct name for a positive ion.” “Candidates are reminded that solid metals react by losing electrons to become cations.”

Worked example 11 mark

An atom forms an ion with a positive charge. Four statements about the atom and the ion are listed.

1 The ion is an anion.

2 The ion is a cation.

3 There are fewer electrons in the ion than in the atom.

4 There are more protons in the ion than in the atom.

Which statements are correct?

A 1 and 3 · B 1 and 4 · C 2 and 3 · D 2 and 4

  1. 1

    C: 2 and 3. A positive ion is a cation, and it has fewer electrons than its atom. [1]

15. The ionic bond

An ionic bond is a strong electrostatic attraction between oppositely charged ions.

The definition is about the attraction that holds the ions together. It does not describe how the ions formed.

Examiner insight

“Many candidates correctly gave the key points that an ionic bond is an attraction between ions and that the attracted ions are of opposite charges. Weaker responses described how an ionic bond forms, describing electron transfer from one atom to another in order to form complete octets.”

Worked example 12 marks

Nickel(II) chloride is a compound with ionic bonding. State the meaning of the term ionic bond.

  1. 1

    (strong) electrostatic attraction [1]

  2. 2

    between oppositely charged ions [1]

16. Ionic bonds from Group I and Group VII

A sodium atom, in Group I, loses its one outer electron. It becomes the cation Na⁺. A chlorine atom, in Group VII, gains that electron. It becomes the anion Cl⁻. Each ion has 8 electrons in its outer shell.

In a dot-and-cross diagram of sodium chloride, the sodium ion has 8 crosses in its outer shell. The chloride ion has 7 dots and 1 cross. The cross is the electron from sodium. The charge is written on each ion.

Na → Na⁺ + e⁻

Cl + e⁻ → Cl⁻

Examiner insight

“The link between group number and the ion of the elements or the formation of ionic bonds from Group I elements was not well recalled.” “It was common for there to be errors in the numbers of electrons (or the symbols used for them) in the outer shells of each ion.”

Worked example 13 marks

Sodium, in Group I, reacts with chlorine, in Group VII, to form sodium chloride. Describe, in terms of electrons, how the sodium ion and the chloride ion form.

  1. 1

    a sodium atom loses one electron to form Na⁺ [1]

  2. 2

    a chlorine atom gains that electron to form Cl⁻ [1]

  3. 3

    both ions have 8 electrons in the outer shell [1]

17. Properties of ionic compounds

Ionic compounds have high melting points and high boiling points.

They conduct electricity when molten or in aqueous solution. They are poor conductors when solid. The mark scheme also credits that an ionic compound can be soluble in water.

Examiner insight

“However, many candidates just stated ‘conducts electricity’ without also stating the conditions of when molten or in aqueous solution.” “Candidates should know that ‘high melting point’ and ‘high boiling point’ are not considered as two separate marking points and together or separately would only gain one mark.”

Worked example 12 marks

Potassium iodide is an ionic compound. State two physical properties of an ionic compound other than solubility in water.

  1. 1

    high melting point / high boiling point [1]

  2. 2

    conducts electricity when molten / when in aqueous solution [1]

18. The giant ionic lattice

An ionic compound has a giant lattice structure. It is a regular arrangement of alternating positive and negative ions.

Ionic describes the bonding. Lattice describes the structure. Give both ideas, and name the ions.

Examiner insight

“Attempts to explain the term ionic lattice required candidates to state that positive and negative ions are arranged in a regular pattern rather than simply using the terms ionic and/or lattice that were given in the question.” “Candidates should be aware that ‘ionic’ is a type of bonding as opposed to a type of structure.”

Worked example 12 marks

Sodium chloride and silicon(IV) oxide both have a lattice structure. Describe the arrangement of ions in sodium chloride.

  1. 1

    a regular arrangement of alternating ions [1]

  2. 2

    positive and negative ions [1]

19. Ionic bonds from metals and non-metals

A metal atom loses electrons to form a cation. A non-metal atom gains electrons to form an anion. The ions can carry more than one charge.

In magnesium fluoride, the magnesium atom loses two electrons to form Mg²⁺. Each fluorine atom gains one electron to form F⁻. Two fluoride ions balance one magnesium ion, so the formula is MgF₂.

In the dot-and-cross diagram the magnesium ion is 2,8 with all crosses. Each fluoride ion is 2,8 with 7 dots and 1 cross in its outer shell. In sodium oxide the oxide ion, O²⁻, has 6 dots and 2 crosses. In magnesium sulfide the ions are Mg²⁺ and S²⁻.

Mg → Mg²⁺ + 2e⁻

S + 2e⁻ → S²⁻

Examiner insight

“The most common errors seen were: drawing the electronic configurations of the magnesium and fluorine atoms rather than the ions; showing the fluoride ion as having all dots in the outer shell instead of seven dots and one cross; drawing an extra third shell on the fluoride ion.” “The most common errors seen were: leaving charges in the formula; word equations or sentences instead of formulae; using the symbol Fl for fluorine in the formula.”

Worked example 14 marks

Magnesium, in Group II, reacts with fluorine, in Group VII. Describe how the ions form and give the formula of magnesium fluoride.

  1. 1

    a magnesium atom loses two electrons to form Mg²⁺ [1]

  2. 2

    each fluorine atom gains one electron to form F⁻ [1]

  3. 3

    two F⁻ ions balance the 2+ charge of one Mg²⁺ ion [1]

  4. 4

    formula MgF₂, with no charges written [1]

20. Explaining the properties of ionic compounds

Ionic compounds have high melting and boiling points because there are strong forces of attraction between oppositely charged ions throughout the giant lattice.

When solid, the ions are in fixed positions and cannot move. When molten or in aqueous solution the ions move, so the compound conducts. Name ions, never molecules or electrons.

Examiner insight

“Many candidates contradicted ‘ionic bonding’ as they introduced covalency into their response with phrases such as ‘NaCl has ionic bonding with strong inter-molecular forces’.” “‘Free ions’ did not gain credit as it is not clear what they are free from. ‘Ions are free to move’, however, is creditworthy.”

Worked example 13 marks

Magnesium fluoride is an ionic compound.

(a)(ii) Explain why magnesium fluoride has a high melting point.

(a)(iii) Explain why magnesium fluoride conducts electricity when it is molten.

  1. 1

    strong forces of attraction / strong bonds [1]

  2. 2

    between oppositely charged ions [1]

  3. 3

    ions move when molten (not when solid) [1]

Recap

  • A positive ion is a cation. A negative ion is an anion.
  • Metal atoms lose electrons to form cations. Non-metal atoms gain electrons to form anions.
  • An ionic bond is a strong electrostatic attraction between oppositely charged ions.
  • Ionic compounds: high melting and boiling points; conduct when molten or aqueous, not solid.
  • Extended: a giant lattice is a regular arrangement of alternating positive and negative ions.
  • Extended: strong attraction between oppositely charged ions; ions move when molten or aqueous.

21. The covalent bond

A covalent bond is formed when a pair of electrons is shared between two atoms. Each atom ends up with a noble gas electronic configuration.

A hydrogen atom has one electron. Sharing one pair gives each hydrogen atom two electrons, the same as helium.

shared electrons = 2 × number of shared pairs

Examiner insight

“Nearly all candidates knew a covalent bond involved sharing electrons; only a very small minority knew it involved sharing a pair of electrons.”

Worked example 12 marks

Describe how the two atoms in a molecule of hydrogen, H₂, are held together.

  1. 1

    a pair of electrons is shared between the two atoms [1]

  2. 2

    each atom then has two electrons, a noble gas (helium) configuration [1]

22. Simple molecules: H₂, Cl₂, H₂O, CH₄, NH₃, HCl

In a dot-and-cross diagram, each bonding pair sits between two atoms. Electrons that are not shared are non-bonding electrons, drawn in pairs.

H₂, Cl₂ and HCl have one shared pair. H₂O has two, NH₃ three and CH₄ four.

Chlorine has 6 non-bonding electrons on each atom. Oxygen in H₂O has 4. Nitrogen in NH₃ has 2. Hydrogen atoms never carry non-bonding electrons. Elements such as H₂ and Cl₂ are diatomic: two atoms in a molecule.

Examiner insight

“The commonest errors were to put non-bonding electrons on the hydrogen atoms, to put three electrons in the bonding overlap area or to put one or four non-bonding electrons on the nitrogen atom.” “Weaker responses tended not to show non-bonding electrons as pairs and consequently some of the three F atoms had five or seven non-bonding electrons.”

Worked example 11 mark

What is the total number of shared electrons in one molecule of ammonia?

A 2 · B 4 · C 6 · D 8

  1. 1

    ammonia, NH₃, has three bonds, each one shared pair of electrons

  2. 2

    3 × 2 = 6 shared electrons: C [1]

23. Properties of simple molecular compounds

Simple molecular compounds have low melting points and boiling points. They have poor electrical conductivity.

So a substance with a low melting point that does not conduct is likely to be simple molecular. Between its melting point and boiling point a substance is a liquid. Above its boiling point it is a gas.

Examiner insight

“A common error was to suggest that the more volatile a substance, the higher the boiling point is.” “Other common errors included the suggestion that sodium chloride is a simple covalent molecule or that sodium chloride conducts electricity as a solid.”

Worked example 11 mark

Which row describes the properties of a simple molecular compound?

rowmelting point / °Cboiling point / °Celectrical conductivity at room temperature and pressure
A–39357good
B35504830poor
C11181poor
D97882good
  1. 1

    simple molecular: low melting and boiling points, poor conductivity

  2. 2

    B has very high values; A and D conduct well. The answer is C [1]

24. Double and triple bonds: O₂, CO₂, N₂, C₂H₄, CH₃OH

Some atoms share more than one pair. A double bond is two shared pairs. A triple bond is three.

O₂ has a double bond and 4 non-bonding electrons on each atom. CO₂ has two double bonds, one between carbon and each oxygen. N₂ has a triple bond and 2 non-bonding electrons on each atom.

C₂H₄ has a double bond between its two carbon atoms. Each carbon also bonds to two hydrogen atoms. In CH₃OH carbon bonds to three hydrogen atoms and to oxygen, and oxygen bonds to one hydrogen atom. The oxygen has 4 non-bonding electrons. There are no other non-bonding electrons on carbon or hydrogen.

Examiner insight

“Better performing candidates tended to draw non-bonding electrons in pairs.”

Worked example 13 marks

Describe the bonding in a molecule of nitrogen, N₂. A nitrogen atom has five outer electrons.

  1. 1

    three pairs of electrons are shared between the two atoms: a triple bond [1]

  2. 2

    each nitrogen atom has 2 non-bonding electrons [1]

  3. 3

    each atom has 3 × 2 + 2 = 8 outer electrons, a noble gas configuration [1]

25. Why the properties follow from the structure

The molecules in a simple molecular compound are held to each other by weak intermolecular forces. These are overcome when it melts or boils, so the melting and boiling points are low.

Covalent bonds are strong. They are the bonds between the atoms inside each molecule. They remain unbroken when a simple molecular substance changes state.

A simple molecular compound has no ions. It has many electrons, but none of them are mobile. So its electrical conductivity is poor.

Examiner insight

“A number of answers referred to covalent bonding or bonds between atoms being weak.” “Candidates often referred to covalent bonds and intermolecular forces in tetrafluoromethane without making it clear which ones were broken when the substance melted.”

Worked example 11 mark

Oxygen, O₂, consists of simple molecules.

Oxygen has a low melting point.

State the general term for the weak forces of attraction that cause oxygen to have a low melting point.

  1. 1

    the weak forces act between the molecules, not between the atoms in a molecule

  2. 2

    intermolecular forces of attraction [1]

Recap

  • A covalent bond is a pair of electrons shared between two atoms, giving noble gas configurations.
  • Non-bonding electrons are drawn in pairs. Hydrogen atoms have none.
  • H₂, Cl₂ and HCl: one shared pair. H₂O: two. NH₃: three. CH₄: four.
  • Simple molecular compounds: low melting and boiling points, poor electrical conductivity.
  • Extended: O₂, CO₂ and C₂H₄ have double bonds. N₂ has a triple bond.
  • Extended: low melting points are due to weak intermolecular forces. Covalent bonds stay unbroken. No ions and no mobile electrons, so poor conductivity.

26. Diamond and cutting tools

Diamond is a form of carbon with a giant covalent structure. Each carbon atom has four covalent bonds, and the atoms are held in a lattice.

Diamond is very hard. This property makes it suitable for use in cutting tools.

Examiner insight

“Common incorrect or incomplete responses were: ‘giant’ and ‘giant lattice’ both of which did not include the covalent nature of diamond.” “Common errors included cutlery, tools or equipment, which were all too vague; restating types of jewellery, which was included in the stem of the question; or giving lubricant or electrode, which confused diamond with graphite.”

Worked example 11 mark

Give one property of diamond that makes it suitable for use in cutting tools.

  1. 1

    (very) hard [1]

27. Graphite: layers and lubricant

Graphite is another form of carbon with a giant covalent structure, so it has a high melting point. Its atoms are arranged in layers, with a hexagonal arrangement of atoms within each layer.

There are weak attractive forces between the layers, so the layers can slide over each other. This makes graphite soft, and it is why graphite is used as a lubricant.

Examiner insight

“Although the statement describes a correct property of graphite, it does not explain the use of graphite as a lubricant.” “Less well described was the hexagonal arrangement of atoms within these layers.”

Worked example 11 mark

Graphite is a form of carbon. Why can graphite be used as a lubricant?

A Graphite contains unbonded electrons which move through the structure. · B Graphite contains weak covalent bonds, so the atoms move easily. · C Graphite has a low melting point, so it easily turns into a liquid. · D Graphite has weak attractive forces between layers, so they can move.

  1. 1

    D: graphite has weak attractive forces between layers, so they can move. [1]

28. Graphite as an electrode

Graphite conducts electricity because it has mobile electrons.

Graphite is also inert, which means it is unreactive. These two properties make it suitable for use as an electrode. Give both, and write ‘conducts electricity’ in full.

Examiner insight

“The term ‘free electrons’ gained no credit.” “Many stated that graphite was inert or a conductor of electricity. Very few made both statements that were required.”

Worked example 12 marks

Graphite is used as an electrode in electrolysis. Give two properties of graphite that make it suitable for this use.

  1. 1

    conducts electricity [1]

  2. 2

    inert / unreactive [1]

29. Silicon(IV) oxide

Silicon(IV) oxide, SiO₂, is a compound with a giant covalent structure. It is a lattice of silicon and oxygen atoms joined by covalent bonds.

Each silicon atom has four bonds and each oxygen atom has two. The structure is not a giant ionic lattice, and it is not simple covalent.

Examiner insight

“Over half of the candidates assumed that silicon(IV) oxide is a giant ionic lattice rather than a giant covalent lattice and chose Distractor A.” “Most candidates recalled the covalent nature of SiO2 but went on to choose option C, simple covalent.”

Worked example 12 marks

Describe the structure of silicon(IV) oxide, SiO₂.

  1. 1

    a giant covalent structure / lattice [1]

  2. 2

    of silicon and oxygen atoms joined by covalent bonds [1]

30. Diamond and silicon(IV) oxide compared

Diamond and silicon(IV) oxide both have a giant covalent lattice. The carbon in diamond and the silicon in silicon(IV) oxide each have four covalent bonds.

Because their structures are similar, their properties are similar. Both have a high melting point. To explain it, say that the bonding is covalent, that it is strong, and that the structure is giant. There are no molecules, so do not write about intermolecular forces.

Examiner insight

“Better performing candidates identified the bonding as covalent, described the bonding as strong and correctly identified the type of structure as giant or macromolecular.” “There were many references to intermolecular forces in silicon(IV) dioxide.”

Worked example 11 mark

How are the structures of diamond and silicon(IV) oxide similar?

A Molecules of both diamond and silicon(IV) oxide are held together by weak attractive forces. · B They both contain atoms arranged in planes held together by weak bonds. · C They both contain ions that are free to move. · D The carbon in diamond and the silicon in silicon(IV) oxide each have four covalent bonds.

  1. 1

    D: the carbon in diamond and the silicon in silicon(IV) oxide each have four covalent bonds. [1]

Recap

  • Diamond: giant covalent, four covalent bonds per carbon atom, very hard, used in cutting tools.
  • Graphite: giant covalent, layers of carbon atoms, high melting point.
  • Graphite is a lubricant because there are weak attractive forces between layers, so they slide.
  • Graphite is an electrode because it conducts electricity (mobile electrons) and is inert: give both.
  • Extended: silicon(IV) oxide, SiO₂, is a giant covalent lattice of atoms, with four bonds on each silicon atom and two on each oxygen atom.
  • Extended: diamond and silicon(IV) oxide both have a high melting point, because the covalent bonding is strong and the structure is giant.

31. What metallic bonding is

Metallic bonding is the electrostatic attraction between the positive ions in a giant metallic lattice and a ‘sea’ of delocalised electrons.

Three ideas must all be present: the positive ions in a lattice, the electrons, and the attraction between these oppositely charged particles.

In magnesium the ions are Mg²⁺.

Examiner insight

“‘Force’ and ‘electrostatic’ both need to be qualified by reference to ‘attraction’.” “Candidates often omitted reference to attraction between positive ions and electrons.”

Worked example 13 marks

Describe metallic bonding.

  1. 1

    a giant lattice of positive ions [1]

  2. 2

    a ‘sea’ of delocalised electrons [1]

  3. 3

    electrostatic attraction between the positive ions and the electrons [1]

32. Which particles are in the lattice

The lattice in a metal is made of positive ions. They are not atoms, not protons and not negative ions.

The electrons are the negative particles. They move in the spaces between the ions. A metal has no negative ions.

This is why metallic bonding is different from ionic bonding, where a lattice holds both positive and negative ions.

Examiner insight

“Candidates knew the phrase ‘sea of electrons’ but incorrectly thought the lattice was comprised of negative ions.” “Many omitted the idea that the positive ions were held in a lattice.”

Worked example 11 mark

Solid X and solid Y are both pure substances that contain ions. X is not an electrical conductor. Y is an electrical conductor. Which statements about X and Y are correct?

1 X is a compound. Y is an element.

2 The ions in X are held in a lattice. The ions in Y are not held in a lattice.

3 X contains both positive and negative ions. Y contains positive ions but no negative ions.

A 1, 2 and 3 · B 1 and 2 only · C 1 and 3 only · D 2 and 3 only

  1. 1

    C: statements 1 and 3 only. Statement 2 is wrong because the ions in Y, a metal, are also held in a lattice. [1]

33. Electrical conductivity

A metal conducts electricity because it has mobile electrons. They can move throughout the structure.

The electrons are charged. Their movement in a given direction is the current. They do not pass charge on.

Examiner insight

“Reference to movement of electrons or mobile electrons was essential in the answer to this question.” “Many candidates limited their answer to the electrons being delocalised which was insufficient, as many organic compounds contain delocalised electrons but are not conductors of electricity.”

Worked example 12 marks

Explain, in terms of structure, why magnesium conducts electricity.

  1. 1

    magnesium has a ‘sea’ of delocalised electrons [1]

  2. 2

    these electrons are mobile: they move throughout the structure [1]

34. Malleability and ductility

A metal is malleable: it can be hammered into shape. It is also ductile: it can be drawn into a wire.

The structure explains both. The layers of positive ions can slide over each other. A vague answer such as ‘the bonds are not difficult to break’ does not explain it.

Examiner insight

“Most candidates recognised the description of ‘malleability’, although ‘ductile’ was a common error.” “Most candidates appreciated that the key point to this response was that layers of particles (positive ions) can slide over one another.”

Worked example 11 mark

Which row describes the structure of a solid metal and explains the property?

structure of solid metalproperty of solid metal
Alattice of negative ions in a sea of electronsconducts electricity because the electrons are free to move
Blattice of negative ions in a sea of electronsis malleable because the layers of ions can slide over each other
Clattice of positive ions in a sea of electronsconducts electricity because the ions are free to move
Dlattice of positive ions in a sea of electronsis malleable because the layers of ions can slide over each other
  1. 1

    D. A and B are wrong because the lattice is made of positive ions. C is wrong because the electrons move, not the ions. [1]

Recap

  • Extended: metallic bonding is the electrostatic attraction between the positive ions in a giant metallic lattice and a ‘sea’ of delocalised electrons.
  • Extended: a metal lattice holds positive ions only. The electrons are the negative particles.
  • Extended: metals conduct electricity because the electrons are mobile and move throughout the structure.
  • Extended: metals are malleable and ductile because the layers of positive ions slide over each other.

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

  1. State what is meant by an element.1 mark
  2. Potassium chloride has the formula KCl. State whether it is an element or a compound. Give a reason.2 marks
  3. State whether each substance is an element, a compound or a mixture: N₂, CO₂, brass, Cl₂.4 marks
  4. A student says, “Brass is a compound of copper and zinc.” Explain why the student is wrong.2 marks
  5. Water, H₂O, is a compound and not a mixture of hydrogen and oxygen. State what shows this.2 marks
  6. Clean, dry air is approximately 78% nitrogen. State whether air is an element, a compound or a mixture, and give a reason.2 marks
  7. A student describes a hydrocarbon as “it contains hydrogen and carbon”. Explain why this does not show it is a compound.2 marks
  8. A gas jar holds three sorts of particle. The first sort is a pair of nitrogen atoms. The second sort is one carbon atom joined to two oxygen atoms. The third sort is two hydrogen atoms joined to one oxygen atom. (a) Classify the contents of the jar. (b) Classify each of the three substances. (c) State how many different elements are present, and name them.5 marks
  9. Sterling silver is an alloy. It is made by melting silver with a small amount of copper and letting the liquid cool. A student writes: “Sterling silver contains two elements, so it is a compound, like copper oxide.” (a) Classify silver, sterling silver and copper oxide as an element, a compound or a mixture. (b) Explain what is wrong with the student’s reason.5 marks
  10. Ammonia, NH₃, is made from nitrogen and hydrogen. Four gas jars, W, X, Y and Z, are filled at different stages of the process. The table lists every sort of particle in each jar. (a) Classify the contents of each jar as an element, a compound or a mixture. (b) Jars W and X both contain only nitrogen atoms and hydrogen atoms. Explain why they are classified differently. (c) For jar Y, state the number of different elements and the number of different substances. | jar | particles present | | --- | --- | | W | NH₃ only | | X | N₂ and H₂ | | Y | NH₃, N₂ and H₂ | | Z | H₂ only |8 marks
  11. State the relative charge and the relative mass of a neutron.2 marks
  12. Describe where the protons, neutrons and electrons are in an atom.2 marks
  13. Define proton number.1 mark
  14. An atom of chlorine has 17 protons and a nucleon number of 35. Deduce the number of electrons and the number of neutrons in the atom.2 marks
  15. Aluminium has proton number 13. Write its electronic configuration, then state its group number and its period number.3 marks
  16. A sodium ion, Na⁺, has proton number 11 and nucleon number 23. Deduce the number of protons, neutrons and electrons in the ion.3 marks
  17. Magnesium has proton number 12. Write the electronic configuration of a magnesium atom and of a magnesium ion, Mg²⁺.2 marks
  18. An oxide ion, O²⁻, has proton number 8 and nucleon number 16. Deduce its number of protons, neutrons and electrons, and write its electronic configuration.4 marks
  19. The table gives the numbers of particles in four different particles, W, X, Y and Z. The letters are not chemical symbols. (a) State which particle is an atom. Give a reason. (b) Deduce the charge on particle W and the charge on particle Z. (c) State which two particles have the same nucleon number. (d) One particle is an ion of an element in Group I. Identify the particle and explain your answer. | particle | protons | neutrons | electrons | | --- | --- | --- | --- | | W | 16 | 16 | 18 | | X | 18 | 22 | 18 | | Y | 19 | 20 | 18 | | Z | 20 | 20 | 18 |6 marks
  20. An ion X²⁻ contains 18 electrons and 18 neutrons. X is not a chemical symbol. (a) Deduce the proton number of X. (b) Deduce the nucleon number of this ion. (c) Write the electronic configuration of an atom of X. (d) State the group number and the period number of X. (e) A different ion, Y²⁺, also contains 18 electrons. A student says that X and Y are in the same period because their ions have the same electronic configuration. Explain why the student is wrong.7 marks
  21. Define the term isotopes.2 marks
  22. An atom has the symbol ^{23}_{11}Na. State the number of protons, neutrons and electrons in the atom.3 marks
  23. Atom P has 8 protons and 8 neutrons. Atom Q has 8 protons and 10 neutrons. State whether P and Q are isotopes of the same element. Give a reason.2 marks
  24. An ion has the symbol ^{32}_{16}S²⁻. State the number of protons, neutrons and electrons in the ion.3 marks
  25. Atom R has 17 protons and 18 neutrons. Atom S has 18 protons and 18 neutrons. Atom T has 17 protons and 20 neutrons. Identify the two atoms that are isotopes of the same element. Give a reason.2 marks
  26. A magnesium ion has 12 protons, 12 neutrons and 10 electrons. Write the symbol for this ion. Show its nucleon number, its proton number and its charge, in the same way as ^{35}_{17}Cl⁻.3 marks
  27. Chlorine has two isotopes, ^{35}_{17}Cl and ^{37}_{17}Cl. Both isotopes react with sodium in the same way. Explain why the two isotopes have the same chemical properties.2 marks
  28. A sample of lithium contains two isotopes, ^{6}Li and ^{7}Li. The table shows the relative abundances of the two isotopes in the sample. Calculate the relative atomic mass of this sample of lithium to one decimal place. | isotope | ^{6}Li | ^{7}Li | | --- | --- | --- | | relative abundance | 1 | 12 |2 marks
  29. A mineral contains strontium. The strontium in the mineral has three isotopes. The table shows the percentage abundances of two of them. (a) Calculate the percentage abundance of ^{88}Sr. [1] (b) Calculate the relative atomic mass of the strontium in the mineral to one decimal place. [2] (c) In the mineral, strontium is present as ions. Deduce the number of neutrons and the number of electrons in one ^{88}_{38}Sr²⁺ ion. [2] | isotope | ^{86}Sr | ^{87}Sr | ^{88}Sr | | --- | --- | --- | --- | | percentage abundance | 10 | 7 | |5 marks
  30. Rubidium has two isotopes, ^{85}Rb and ^{87}Rb. The relative atomic mass of rubidium is 85.5. (a) Calculate the percentage abundance of ^{85}Rb. [2] (b) A laboratory removes some of the ^{85}Rb atoms from a sample of rubidium. The new sample has 3 atoms of ^{85}Rb for every 2 atoms of ^{87}Rb. Calculate the relative atomic mass of the new sample to one decimal place. [2] (c) A student says the new sample will react differently with water because its relative atomic mass has changed. Explain why the student is wrong. [2]6 marks
  31. State the name of a positive ion and the name of a negative ion.2 marks
  32. A lithium atom forms a lithium ion, Li⁺. Compare the number of electrons and the number of protons in the ion with those in the atom.2 marks
  33. A student writes: ‘An ionic bond is the transfer of electrons from one atom to another.’ Explain why this does not define an ionic bond, and write a correct definition.2 marks
  34. Potassium is in Group I and bromine is in Group VII. They react to form potassium bromide. Describe what happens to the electrons, and give the formula of each ion formed.3 marks
  35. Sodium is in Group I and fluorine is in Group VII. Write the formula of sodium fluoride and give the charge on each ion.2 marks
  36. A student tests the electrical conductivity of potassium bromide. State the result for the solid, for the molten compound and for an aqueous solution.3 marks
  37. Describe the structure of a giant ionic lattice.2 marks
  38. Magnesium is in Group II and oxygen is in Group VI. They react to form magnesium oxide. Describe how the ions form, give their charges and write the formula of the compound.4 marks
  39. Element X is a metal in Group III. Element Y is a non-metal in Group VI. They react to form an ionic compound. A student describes a dot-and-cross diagram of the compound: ‘X has 3 crosses in its outer shell. Y has 6 dots in its outer shell. The formula is X³⁺Y²⁻.’ (a) State what is wrong with the student’s description of the outer shells. [1] (b) Describe the outer shell of one ion of Y. Use dots for the electrons of Y and crosses for the electrons from X. [1] (c) Deduce the correct formula of the compound. Explain your answer using the numbers of electrons lost and gained. [3]5 marks
  40. A student tests three solids, P, Q and R. The table below gives the results. (a) Identify the ionic compound. Give two pieces of evidence from the table. [3] (b) The student writes: ‘The ionic compound has a high melting point because there are strong intermolecular forces between its molecules. It conducts when molten because its electrons are free to move.’ Write a correct explanation of both properties. [3] (c) The ionic compound dissolves in water. Predict whether the solution conducts electricity. Explain your answer. [1] | solid | melting point / °C | conducts when solid | conducts when molten | | --- | --- | --- | --- | | P | 1263 | no | yes | | Q | 115 | no | no | | R | 1455 | yes | yes |7 marks
  41. State what is shared in a covalent bond.1 mark
  42. Explain why two hydrogen atoms bond covalently to form H₂.2 marks
  43. A chlorine atom has seven outer electrons. In a molecule of Cl₂, state the number of shared pairs and the number of non-bonding electrons on each atom.2 marks
  44. An oxygen atom has six outer electrons. In a molecule of H₂O, state the number of non-bonding electrons on the oxygen atom.2 marks
  45. Describe the dot-and-cross diagram of a molecule of ammonia, NH₃. State the number of bonding pairs, the number of non-bonding electrons on nitrogen and the number on each hydrogen atom.3 marks
  46. Hydrogen gas reacts with chlorine gas to form hydrogen chloride gas. Write a balanced equation with state symbols.2 marks
  47. Compound X has a melting point of –23 °C and a boiling point of 77 °C. It does not conduct electricity. State the type of compound and its physical state at 50 °C.3 marks
  48. A carbon atom has four outer electrons and an oxygen atom has six. State the type of bond between carbon and each oxygen in CO₂, the total number of shared electrons in one molecule and the number of non-bonding electrons on each oxygen atom.3 marks
  49. Chloroethene, C₂H₃Cl, is a simple molecule. The two carbon atoms are joined by a double bond. One carbon atom is also bonded to two hydrogen atoms. The other is also bonded to one hydrogen atom and one chlorine atom. A carbon atom has four outer electrons, a hydrogen atom one and a chlorine atom seven. (a) Calculate the total number of shared electrons in one molecule. (b) Calculate the total number of non-bonding electrons in one molecule. State which atom they are on. (c) Use the number of shared pairs to explain why each carbon atom has a noble gas electronic configuration.5 marks
  50. Phosphine, PH₃, is a simple molecular compound. It melts at –133 °C and boils at –88 °C. (a) Deduce the physical state of phosphine at –100 °C. Give a reason. (b) A student writes: ‘Phosphine boils at a low temperature because its covalent bonds are weak and break.’ Identify the two errors and give the correct explanation. (c) Explain why liquid phosphine has poor electrical conductivity.7 marks
  51. State the type of structure that diamond has.1 mark
  52. Describe the arrangement of the atoms in graphite.2 marks
  53. Graphite is used as a lubricant in machines. Explain why, using its structure.2 marks
  54. Graphite is used to make electrodes. Give two properties of graphite that make it suitable.2 marks
  55. The tip of a drill is coated with one form of carbon so that it can cut through rock. State which form of carbon is used and give the property that makes it suitable.2 marks
  56. A student writes: ‘Graphite is soft because it contains weak covalent bonds.’ Explain what is wrong with this statement.2 marks
  57. The table gives properties of two forms of carbon, X and Y. Identify X and Y and give one use for each. | | X | Y | | --- | --- | --- | | hardness | very hard | soft | | conducts electricity when solid | no | yes | | melting point | high | high |4 marks
  58. A student says: ‘Silicon(IV) oxide has a low melting point because weak intermolecular forces hold its molecules together.’ Explain why this is wrong.4 marks
  59. In silicon(IV) oxide every silicon atom is bonded only to oxygen atoms, and every oxygen atom is bonded only to silicon atoms. (a) State the number of covalent bonds on each silicon atom and on each oxygen atom. [2] (b) Use your answers to show that the lattice contains two oxygen atoms for every silicon atom. [2]4 marks
  60. The table describes four solids, P, Q, R and S. All four are covalent and none contains ions. One is silicon(IV) oxide, one is diamond and one is graphite. (a) Identify silicon(IV) oxide. Give a reason for rejecting each of the other three solids. [3] (b) Identify diamond. Give a reason for your choice. [1] (c) Explain, in terms of structure and bonding, why silicon(IV) oxide and diamond both have a high melting point. [3] | | P | Q | R | S | | --- | --- | --- | --- | --- | | element or compound | element | compound | compound | element | | melting point | high | high | low | high | | conducts electricity when solid | no | no | no | yes |7 marks
  61. State what is meant by metallic bonding.3 marks
  62. Magnesium is a metal. Give the formula of its positive ion and name the particles that this ion is attracted to.2 marks
  63. A student writes: ‘A metal is a lattice of protons in a sea of electrons.’ Correct the error.1 mark
  64. A student writes: ‘Metals conduct electricity because they contain free electrons.’ Explain why this earns no credit, and write an answer that does.2 marks
  65. Copper can be drawn into thin wires. Name this property and explain it in terms of structure.2 marks
  66. Aluminium foil can be pressed into the shape of a tray. A student explains: ‘The bonds in a metal are not difficult to break, so the atoms move away easily.’ Give two corrections to the explanation.2 marks
  67. Solid Y is an element. It conducts electricity and it contains ions. A student says: ‘Y must contain both positive and negative ions.’ Explain why this is wrong, and explain how Y conducts electricity.3 marks
  68. Aluminium is a metal in Group III. A student draws its bonding as a lattice of neutral atoms with electrons circling each atom, and labels it ‘held together by a force’. Give three corrections.3 marks
  69. A strip of zinc is bent and then connected in a circuit, where it conducts. A student writes: ‘Bending shows that the ions in zinc can move. So zinc conducts because its ions move through the metal, passing charge from one to the next.’ Explain what is right and what is wrong in this answer.4 marks
  70. Gold is a metal. A craftsman hammers a block of gold into a very thin sheet called gold leaf. The gold leaf still conducts electricity. A student writes: ‘Gold is ductile because its atoms are free to move. The leaf conducts because gold has delocalised electrons.’ (a) Give three corrections to the student’s answer. (b) Describe the bonding in the gold leaf.5 marks

Go deeper

Practise and revise with member-only material for this chapter.

Workbook

Exam-style practice questions with full worked solutions.

Unlock with a plan

Chapter at a Glance

A single-page summary of every key idea for fast revision.

Unlock with a plan

Free notes are just the start.

Unlock every Workbook and Chapter at a Glance, and generate your own worksheets and predicted papers.

Explore plans

Related chapters

Solids, liquids and gasesFormulaeElectrolysisExothermic and endothermic reactionsPhysical and chemical changesThe characteristic properties of acids and bases