Lesson 13A.2

13A.2 Polarisation of ions Quiz: Pearson Edexcel Chemistry, Unit 13

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 13A.2, Polarisation of ions: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 13: Energetics II, written with Revision Ninja.

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The 20 questions

  1. What is meant by polarisation of an ion?

    • The movement of electrons from a cation to an anion during electrolysis
    • The increase in size of a cation when it gains electrons
    • The distortion of an anion's electron cloud by the electric field of a nearby cation
    • The separation of charges in a polar covalent molecule by an external field

  2. What two properties determine the polarising power of a cation?

    • Its radius only, because larger cations spread their charge and so polarise anion clouds more strongly
    • Its number of neighbouring anions in the lattice, regardless of the charge carried by each cation
    • Its charge and its mass, because heavier cations hold their electrons more loosely and polarise more strongly
    • Its charge and its radius, giving a high charge density when the charge is high and the radius small

  3. How does the polarisability of an anion depend on its size and charge?

    • It depends only on the mass of the anion
    • It is greatest for small, singly charged anions
    • It decreases with larger radius because the outer electrons are held more tightly
    • It increases with larger anion radius and higher negative charge

  4. Which cation is the most polarising among Na+, Mg2+ and Al3+?

    • K+, because it has the smallest charge density
    • Mg2+, because it has the same charge as O2- so it does not polarise
    • Al3+, because it is small and highly charged
    • Na+, because it has the largest radius

  5. Which anion is the most polarisable among F-, Cl- and I-?

    • I-, because it is large and has a diffuse electron cloud
    • O2-, because its radius is the smallest of the ions listed
    • Cl-, because it has the highest charge density
    • F-, because it is the smallest halide ion

  6. What effect does polarisation have on the bonding in an ionic lattice?

    • It introduces covalent character
    • It lowers the charge on each ion to zero in the lattice
    • It converts the lattice into a metallic solid with free electrons
    • It makes the bonding perfectly ionic by removing all shared electron density

  7. Which pair of compounds is most likely to show significant covalent character from polarisation?

    • KCl, because K+ has a high charge density and Cl- is a large anion that is easily polarised
    • AgI, because Ag+ is small and polarising and I- is large and polarisable
    • NaF, because F- is a small, highly charged anion that is strongly polarising towards Na+
    • MgO, because Mg2+ and O2- are both small, and the lattice is held together by strong covalent sharing

  8. Which of LiCl, NaCl and KCl is expected to show the most covalent character?

    • All three are equally ionic because they share the same anion
    • NaCl, because sodium lies between lithium and potassium
    • KCl, because K+ has the largest ionic radius
    • LiCl, because Li+ is the smallest and most polarising of the three cations

  9. Why is AlCl3 more covalent than NaCl?

    • AlCl3 is only ionic in aqueous solution, so it is covalent when solid
    • Al3+ has a larger radius, so it holds its electrons less tightly
    • Al3+ has a high charge density and polarises the large Cl- ion
    • Cl- in AlCl3 carries a higher charge than in NaCl

  10. Which change would most increase the covalent character of a sodium halide?

    • Replacing Cl- with F- to give NaF, since fluoride is more polarisable
    • Replacing Na+ with Cs+ to give CsCl, since caesium is more polarising
    • Replacing NaCl with KCl, since K+ is more polarising than Na+
    • Replacing Cl- with I- to give NaI, since iodide is far more polarisable

  11. An ionic compound has an experimental lattice energy 150 kJ mol-1 more exothermic than its theoretical ionic value. What is the most justified conclusion?

    • The lattice energy data contains an error, so the Born-Haber cycle must be wrong
    • The compound must be a gas, so its lattice energy is always positive
    • The compound contains only Group 1 metals, which always show extra exothermicity
    • The bonding has significant covalent character

  12. Arrange the sizes of the cations Na+ (about 102 pm), Mg2+ (about 72 pm) and Al3+ (about 53 pm) in order of increasing polarising power.

    • Al3+ < Na+ < Mg2+
    • Al3+ < Mg2+ < Na+
    • Mg2+ < Na+ < Al3+
    • Na+ < Mg2+ < Al3+

  13. A student claims polarising power depends only on the charge of a cation. Which correction is best?

    • Polarising power depends on the number of electrons in the anion
    • Polarising power is independent of charge and depends only on the anion radius
    • Polarising power depends on both charge and radius, so charge density is the key factor
    • Polarising power depends only on the mass of the cation

  14. Why is LiI more covalent than LiF?

    • I- is large and highly polarisable
    • F- is more polarisable than I- because it has a higher electronegativity
    • Li+ has a larger charge in LiI, so its polarising power is higher
    • LiF is covalent because F- has more electrons to share with lithium

  15. A teacher says ionic compounds are perfectly ionic. Which evaluation is best?

    • Correct, because only covalent compounds can show polarisation, so ionic compounds must be perfectly ionic
    • Incorrect, because all metal halides are molecular at room temperature and so are not ionic at all
    • Incorrect, because polarisation introduces covalent character, so real bonding lies between the ionic and covalent extremes
    • Correct, because all ions are perfectly spherical and so cannot be distorted by an electric field at all

  16. Which pair of cations would be expected to polarise anions more strongly: Mg2+ or Ca2+?

    • Ca2+, because its larger size spreads the charge more evenly and so it polarises anions more strongly
    • Mg2+ and Ca2+ are equally polarising, because both carry 2+ charge and differ only in their electron count
    • Mg2+, because its smaller radius gives a higher charge density than Ca2+ of the same charge
    • Ca2+, because it has more electrons available to polarise the anion and so distorts it more

  17. Which combination of ion properties would maximise the covalent character of an ionic compound?

    • A small, low-charged cation paired with a small anion that is not easily polarised by any cation
    • A small, highly charged cation with a large, highly charged anion
    • A large cation with a large, low-charged anion, which gives strong covalent character
    • A large, low-charged cation with a small, low-charged anion, which gives the most ionic bonding

  18. Which compound is more covalent: AgCl or NaCl?

    • Both are equally covalent, because both contain the chloride ion, whose electron cloud is the same in each
    • NaCl, because sodium has a lower first ionisation energy than silver, so its bonds are more covalent
    • AgCl, because the small, polarising Ag+ cation distorts the chloride electron cloud more than Na+ does
    • NaCl, because silver chloride is a metallic compound with delocalised electrons across its lattice

  19. Which compound would be expected to show more covalent character: MgF2 or MgI2?

    • Both are equally covalent because both contain Mg2+
    • MgF2, because F- is the most electronegative halide ion
    • MgI2, because I- is large and easily polarised by Mg2+
    • Neither compound contains an ionic bond

  20. Which cation has the greater polarising power: a 3+ ion of radius 60 pm or a 2+ ion of radius 70 pm?

    • The 2+ ion, because its larger radius gives greater polarising power
    • The 2+ ion, because polarising power decreases as charge increases
    • They are equally polarising because the radii are similar
    • The 3+ ion, because 3/60 gives a higher charge density than 2/70

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