Edexcel A-Level Chemistry AS Paper 1, June 2023: Question 5

9 marks · Medium difficulty · Open Response

Discuss electronegativity, its trend in Group 7, the continuum of bonding type, and how Period 3 chloride and chlorine data demonstrate this bonding continuum.

Practise this question

Question

Question text

5 The question is about electronegativity and its influence on bonding.

(a) State what is meant by the term electronegativity.

(1)

(b) Explain the trend in electronegativity for the Group 7 elements.

(3)

relation to electronegativities.

(2)

(d) The table gives data for chlorine and chlorine compounds of some Period 3

12 elements. The data show evidence that the type of bonding in compounds is a

continuum across Period 3.*P71926A01228*

Empirical formula Melting temperature / °C Electrical conductivity

Sodium chloride NaCl 801 Yes, when molten

Magnesium chloride MgCl2 714 Yes, when molten

Aluminium chloride AlCl3 No

(sublimes)

Silicon tetrachloride SiCl4 –70 No

Phosphorus(III) chloride PCl3 –112 No

Chlorine Cl2 –102 No

Discuss the extent to which the data in the table demonstrate a continuum of

bonding type.

Include reference to the data of three of the substances in the table with different

types of bonding.

(3)

(Total for Question 5 = 9 marks)

Mark scheme

Show the mark scheme

Question Answer Additional Guidance Mark

Number

5(a) An answer that makes reference to the following (1)

point:

• (electronegativity is) the ability of an atom Allow the ability of an atom to attract the bonding electrons from a

to attract the (bonding / shared) pair of covalent bond

electrons (in a covalent bond) Do not award an electron instead of pair of electrons

Number

5(b) An answer that makes reference to the following Allow reverse arguments for trend being more electronegative up (3)

points: the group

• less electronegative down the group (1)

• because the (pair of) electrons (in the Allow outer / valence electrons

covalent bond) are further from the nucleus (1) Allow the atomic radius increases down the group

Ignore the ionic radius increases down the group

• with more shielding electrons (1) Allow there are more shells of electrons

Ignore any reference to effective nuclear charge / Do not award the

nuclear charge remains the same

Number

5(c) An answer that makes reference to the following This question may be answered in many different ways. (2)

points:

• (a continuum of bonding) has two extreme Allow ideas such as bonds with low electronegativity difference

bonding types, ionic and covalent are covalent, while those with large difference are ionic.

(1) If values are given ignore the values but accept differences bigger

than x are ionic those smaller than y are covalent for M1.

• electronegativity differences between two Allow ideas such as the electronegativity difference decreases a

atoms of intermediate value result in bond is more covalent, as it increases it is more ionic

intermediate bonding (1) Ignore references to polarity of ions

The higher the difference in electronegativity the more ionic the

compound is (1)

and the lower the difference the more covalent scores (1)

Number

5(d) An answer that makes reference to the following A named substance must be given for each mark. (3)

points: The bonding in each substance should be linked to a property in

the table.

Do not penalise more than 3 correctly named substances

• sodium / magnesium chloride is an ionic Allow is ionically bonded

compound

and (1)

so conducts electricity when molten Allow so has a high melting temperatures

• chlorine / phosphorus(III) chloride / silicon Allow molecular structure

tetrachloride are simple covalent structures Do not award giant molecular structure

Allow is covalently bonded

and

so have low melting temperatures / so do Allow requires little energy to break intermolecular forces

not conduct electricity (when molten) (1)

• aluminium chloride is ionic with covalent Allow it is ionic as a solid but becomes covalent when it sublimes

character / has intermediate bonding Allow aluminium chloride is polar covalent

Allow aluminium chloride has dative covalent bonds

and

so has a low sublimation temperature / so Allow melting temperature for sublimation temperature

does not conducting electricity (1) Allow high melting/sublimation temperature in comparison to the

covalent substances.

Allow high melting/sublimation temperature in comparison to the

ionic substances.

If no other mark awarded allow the bonding goes from ionic to

covalent due to decreasing electrical conductivity / melting

temperatures for (1)

(Total for Question 5 = 9 marks)

How to answer it

Electronegativity and Bonding

📌 What this question tests

This question assesses your understanding of fundamental periodic trends, specifically defining electronegativity and explaining its down-group variation. It also tests your ability to connect electronegativity differences to bonding types, interpreting physical properties (melting points and electrical conductivity) across Period 3 chlorides to demonstrate a bonding continuum.

Part (a) — Defining Electronegativity

Question 5(a): State what is meant by the term electronegativity. (1 mark)

✅ Correct Answer

The ability of an atom to attract the bonding pair of electrons in a covalent bond.

❌ Common Errors

Writing "attract electrons" instead of specifying a pair of electrons, or referring to an "electron" rather than a shared pair. Examiners are strict on this wording for AS level.

Mark scheme note: 1 mark awarded for mentioning both atomic attraction and the bonding/shared pair of electrons in a covalent bond.

Part (b) — Group 7 Electronegativity Trend

Question 5(b): Explain the trend in electronegativity for the Group 7 elements. (3 marks)

💡 Key Knowledge

Electronegativity decreases down Group 7 (from fluorine to iodine).
Atomic radius increases down the group (more electron shells).
Shielding increases down the group, reducing the nucleus's pull on shared electrons.

🧠 Exam Technique

To secure all 3 marks, you must follow a clear cause-and-effect chain: state the trend, mention the increased distance/atomic radius or shells, and link it to increased shielding or weaker attraction from the nucleus.

❌ Common Errors

Do not state that nuclear charge remains the same (nuclear charge actually increases down the group, but its effect is outweighed by shielding and distance). Avoid mentioning effective nuclear charge unless used with high precision.

Mark breakdown: 1 mark for decreasing down the group; 1 mark for bonding pair being further from the nucleus (larger atomic radius); 1 mark for more shielding electrons.

Part (c) — The Bonding Continuum

Question 5(c): Describe what you understand by the term 'continuum of bonding type' in relation to electronegativities. (2 marks)

✅ Correct Answer

Bonding has two extremes: ionic and covalent . Electronegativity differences between two atoms of intermediate value result in intermediate bonding types (or polar covalent bonds).

💡 Key Knowledge

Bonds are rarely 100% purely ionic or 100% purely covalent. As the electronegativity difference between bonded atoms changes, the bonding transitions gradually along a spectrum rather than switching abruptly.

Mark breakdown: 1 mark for identifying the two extreme bonding types (ionic and covalent); 1 mark for explaining that intermediate electronegativity differences produce intermediate bonding types.

Part (d) — Period 3 Chlorides Data Analysis

Question 5(d): Discuss the extent to which the data in the table demonstrate a continuum of bonding type. Include reference to the data of three of the substances with different types of bonding. (3 marks)

✅ Correct Answer

You must select three distinct substances covering different bonding types and link them directly to properties from the table:

Sodium chloride (or Magnesium chloride): Ionic compound — has a high melting point and conducts electricity when molten.
Aluminium chloride: Intermediate bonding (ionic with significant covalent character) — exhibits a low sublimation temperature (180 °C) and does not conduct electricity.
Silicon tetrachloride / Phosphorus(III) chloride / Chlorine: Simple covalent structures — have very low melting/boiling points and do not conduct electricity.

🧠 Exam Technique

Make sure you explicitly name the substance, state its bonding type, and quote or reference the corresponding data point (melting temperature / electrical conductivity) to back up your statement.

❌ Common Errors

Avoid using the phrase "giant molecular structure" for simple covalent molecules like SiCl₄ or PCl₃ —use simple molecular structure instead. Ensure every mark is anchored to a named substance from the table.

Mark breakdown: 1 mark for linking an ionic substance to its high melting point/molten conduction; 1 mark for linking covalent substances to low melting points/no conduction; 1 mark for identifying aluminium chloride as intermediate/having covalent character with a low sublimation point.

Topics

Physical Chemistry · Inorganic Chemistry · Topic 2: Bonding and Structure · Topic 4: Inorganic Chemistry and the Periodic Table

Question and mark scheme from the Edexcel A-Level Chemistry examination, AS Paper 1, June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.