Chemical Bonding
11 Grade 10 General Science questions on Chemical Bonding, with worked marking schemes. 11 questions are available on this topic in full.
Question 1
4 marksAtoms form chemical bonds using their valence (outer) electrons.
(a) Explain the role of valence electrons in the formation of an ionic bond. (2 marks)
(b) Explain the role of valence electrons in the formation of a covalent bond. (2 marks)
(4 marks)
Marking scheme
(a) (2 marks) - A metal atom loses (transfers) its valence electron(s) to a non-metal atom, so that each attains a stable noble gas arrangement (1 mark) - This forms positive and negative ions which are held together by strong electrostatic attraction (1 mark) (b) (2 marks) - Two non-metal atoms share pairs of valence electrons, each atom usually contributing one electron to a shared pair, so that each attains a stable octet or duplet (1 mark) - The shared pair is attracted by the nuclei of both atoms, holding the atoms together (1 mark) Total: 4 marks
Question 2
1 markGraphite and diamond are both made of carbon atoms only, yet graphite conducts electricity while diamond does not. Which statement best explains this difference?
A. covalent bonds in graphite are weaker than in diamond
B. each carbon atom in graphite has a free electron
C. carbon atoms in diamond are joined by double bonds
D. diamond is made of ions held in fixed positions
(1 mark)
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3 marksHydrogen has atomic number 1 and oxygen has atomic number 8.
(a) Using dots (•) and crosses (×) to represent electrons, draw a diagram to show the bonding in a molecule of water. Show outer electrons only. (2 marks)
(b) State the number of lone pairs of electrons on the oxygen atom in the molecule. (1 mark)
(3 marks)
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1 markWhen iodine crystals are warmed gently in a dry boiling tube inside a fume cupboard, they quickly change into a purple vapour. Which statement best explains why this happens at a low temperature?
A. the forces between iodine molecules are weak
B. the ions in iodine crystals are easily separated
C. iodine is a metal with loosely held electrons
D. the covalent bonds within iodine molecules are weak
(1 mark)
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Create a free account to see itQuestion 5
3 marksWater (H₂O) boils at 100 °C while hydrogen sulphide (H₂S), which has a larger relative molecular mass, boils at −60 °C. Explain this difference in boiling points.
(3 marks)
Marking scheme
Award 1 mark for each point (3 marks): - Water molecules are held together by hydrogen bonds (because oxygen is small and highly electronegative), in addition to van der Waals forces (1 mark) - Hydrogen sulphide molecules are held together mainly by weak van der Waals forces; hydrogen bonds are stronger than van der Waals forces (1 mark) - More heat energy is therefore needed to separate water molecules, so water boils at a higher temperature (1 mark) Total: 3 marks
Question 6
1 markA metallic bond is best described as the force of attraction between
A. oppositely charged ions held in a lattice
B. metal atoms and the electrons of non-metal atoms
C. positive ions and a sea of delocalised electrons
D. neighbouring atoms that share a pair of electrons
(1 mark)
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Create a free account to see itQuestion 7
4 marksSodium (atomic number 11) reacts with chlorine (atomic number 17) to form sodium chloride, the salt used in cooking.
(a) Write the electron arrangement of a sodium atom and of a chlorine atom. (2 marks)
(b) Using dots (•) and crosses (×), draw a diagram to show how sodium chloride is formed from the two atoms. Show outer electrons only. (2 marks)
(4 marks)
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Create a free account to see itQuestion 8
1 markElement X has atomic number 12 and element Y has atomic number 17. Which of the following correctly gives the formula of the compound formed when X reacts with Y and the type of bond in it?
A. XY₂, ionic bond
B. XY, covalent bond
C. XY₂, covalent bond
D. X₂Y, ionic bond
(1 mark)
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Create a free account to see itQuestion 9
1 markWhich of the following species contains a dative (coordinate) covalent bond?
A. ammonium ion, NH₄⁺
B. methane, CH₄
C. sodium chloride, NaCl
D. water, H₂O
(1 mark)
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4 marksAluminium sufurias and cooking pans made by jua kali artisans are common in Kenyan homes.
(a) State two properties of aluminium that make it suitable for making cooking pans. (2 marks)
(b) Aluminium is protected by a thin layer of aluminium oxide on its surface. Explain why aluminium pans should not be scrubbed with sand or steel wool. (2 marks)
(4 marks)
Marking scheme
(a) Any two of the following, 1 mark each (2 marks): - Good conductor of heat - Low density / light in weight - Resists corrosion - Malleable, so it can be beaten or pressed into shape - High melting point (660 °C), well above cooking temperatures - Strong / does not break easily (b) (2 marks) - Scrubbing wears away the protective oxide layer (1 mark) - The exposed metal then corrodes or reacts with food (especially acidic food), so the pan wears out faster and aluminium may get into the food (1 mark) Total: 4 marks
Question 11
6 marksThe table below gives some properties of four substances W, X, Y and Z. Substance | Melting point (°C) | Conducts when solid | Conducts when molten | Solubility in water W | 1083 | Yes | Yes | Insoluble X | −7 | No | No | Slightly soluble Y | 1710 | No | No | Insoluble Z | 714 | No | Yes | Soluble
(a) Identify the type of structure of each substance. (4 marks)
(b) Explain why substance Y has a very high melting point. (2 marks)
(6 marks)
Marking scheme for this question
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