Edexcel A-Level Chemistry AS 3 Bonding and Structure Questions

Identify the bonding and particles present, draw or interpret the requested representation and connect charge, geometry or intermolecular attraction to the observed property.

Exam points

Draw electron, ionic-lattice or molecular diagrams with correct charges and bonding.
Predict molecular shape and bond angle from electron-pair arrangement and repulsion.
Explain structure and properties through bonding, polarity and intermolecular forces.

Covered syllabus points

3.1—Interpret evidence for the existence of ions 3.2—The formation of ions in terms of loss or gain of electrons 3.3—Draw dot-and-cross diagrams to show electrons in cations and anions 3.4—Ionic crystals as giant lattices of ions 3.5—Ionic bonding is the result of strong net electrostatic attraction between ions 3.6—The effects of ionic radius and ionic charge on the strength of ionic bonding 3.7—Reasons for the trends in ionic radii down a group in the Periodic Table, and for a set of isoelectronic ions 3.8—The meaning of the term ‘polarisation’ as applied to ions 3.9—The polarising power of a cation depends on its radius and charge, and the polarisability of an anion also depends on its 3.10—Covalent bonding is the strong electrostatic attraction between two nuclei and the shared pair of electrons between them 3.11—Draw dot-and-cross diagrams to show electrons in covalent substances 3.12—The different structures formed by giant lattices of carbon atoms 3.13—The meaning of the term ‘electronegativity’ as applied to atoms in a covalent bond 3.14—Ionic and covalent bonding are the extremes of a continuum of bonding type 3.15—Distinguish between polar bonds and polar molecules and predict whether or not a given molecule is likely to be polar 3.16—The principles of the electron-pair repulsion theory, used to interpret and predict the shapes of simple molecules and ions 3.17—The terms ‘bond length’ and ‘bond angle’3.18—And explain the shapes of, and bond angles in, BeCl2, BCl3, CH4, NH3, NH4+, H2O, CO2, gaseous PCl5, SF6 and C2H4 3.19—Apply the electron-pair repulsion theory to predict the shapes of, and bond angles in, molecules and ions analogous to those 3.20—Metals consist of giant lattices of metal ions in a sea of delocalised electrons 3.21—Metallic bonding is the strong electrostatic attraction between metal ions and the delocalised electrons 3.22—The models in 3.20 and 3.21 to interpret simple properties of metals

[Maximum number: 6]

This question is about magnesium, magnesium oxide and magnesium sulfate.

(a)

Magnesium oxide and magnesium sulfate are ionic compounds.

[ 4 ]

(i)

Draw a dot-and-cross diagram to show the bonding in magnesium oxide, MgO .
Show outer electrons only.

[ 2 ]

(ii)

The melting temperatures of magnesium oxide and magnesium sulfate are $2852^{\circ} \mathrm{C}$ and $1124^{\circ} \mathrm{C}$ respectively.

Explain why the melting temperature of magnesium oxide is significantly higher than that of magnesium sulfate.

[ 2 ]

An answer that makes reference to the following points:

- oxide/ $\mathrm{O}^{2-}$ smaller than sulfate/ $\mathrm{SO}_{4}{ }^{2-}$

- stronger (electrostatic) attraction between the ( $\mathrm{Mg}^{2+}$ and $\mathrm{O}^{2-}$ ) ions

Allow just the oxide is smaller or vice versa Do not award comparison with sulfur or sulfide

Allow stronger ionic bond

Allow more energy required to break the ionic bond

Allow reverse argument Ignore reference to lattice energy Ignore reference to distortion/polarisation Any reference to intermolecular forces /covalent bond/molecular structure score 0

(2)

(b)

The table gives some data about the electrical conductivity of magnesium and magnesium oxide.

Table for Question (b) — Edexcel A-Level Chemistry AS

Explain the similarities and differences in the electrical conductivity of the two substances.

[ 2 ]

[Maximum number: 9]

Table for Question 2 — Edexcel A-Level Chemistry AS

(a)

Explain the trend in the ionic radii from the nitride ion to the aluminium ion.

[ 3 ]

(b)

(i)

State the structure and bonding of sodium fluoride.

[ 1 ]

(ii)

Explain how the electrical conductivity of sodium fluoride provides evidence for the existence of ions.

[ 3 ]

(iii)

Explain why the fluoride ion is difficult to polarise.

[ 2 ]

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Covered syllabus points

Question 1

Question (a)

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Question (ii)

Question (b)

Question 2

Question (a)

Question (b)

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Question (ii)

Question (iii)