QUESTIONSHEETS STRUCTURE AND BONDING SHAPES OF MOLECULES AND IONS I SHAPES OF MOLECULES AND IONS II IONIC BONDING TENDING TOWARDS COVALENCY

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1 CHEMISTRY QUESTIONSHEETS AS Level AS TOPIC 4 STRUCTURE AND BONDING Questionsheet 1 Questionsheet 2 Questionsheet 3 Questionsheet 4 Questionsheet 5 Questionsheet 6 Questionsheet 7 Questionsheet 8 Questionsheet 9 Questionsheet 10 Questionsheet 11 Questionsheet 12 Questionsheet 13 Questionsheet 14 Questionsheet 15 Questionsheet 16 Questionsheet 17 IONIC BONDING COVALENT BONDING σ AND π BONDING SHAPES OF MOLECULES AND IONS I SHAPES OF MOLECULES AND IONS II IONIC BONDING TENDING TOWARDS COVALENCY COVALENT BONDING TENDING TOWARDS IONIC BONDING METALLIC BONDING INTERMOLECULAR FORCES PROPERTIES AND BONDING CRYSTAL STRUCTURE CHANGES OF STATE BOILING POINTS OF HYDRIDES SOLUBILITY OF IONIC COMPOUNDS TEST QUESTION I TEST QUESTION II TEST QUESTION III 17 marks 14 marks 15 marks 15 marks 15 marks 17 marks 18 marks 16 marks 14 marks 18 marks 15 marks 15 marks 14 marks 19 marks 13 marks 12 marks 13 marks Authors Trevor Birt Donald E Caddy Andrew Jones Adrian Bond Editors John Brockington Stuart Barker John Brockington Kevin Frobisher Andy Shepherd Stuart Barker Curriculum P ress Curriculum Press Licence Agreement: Paper copies of the A-Level Chemistry Questionsheets may be copied free of charge by teaching staff or students for use within their school, provided the Photocopy Masters have been purchased by their school. No part of these Questionsheets may be reproduced or transmitted, in any other form or by any other means, without the prior permission of the publisher. All rights are reserved. This license agreement is covered by the laws of England and Wales Curriculum Press March Curriculum Press Bank House 105 King Street Wellington Shropshire TF1 1NU

2 TOPIC 4 Questionsheet 1 IONIC BONDING a) Define the term ionic bond. b) The formation of an ionic bond in sodium fluoride can be represented by: Na + F Na + F Complete each of the following equations in the same format. (i) Ba + F Ba + O (iii) K + F (iii) K + O c) Explain why ionic compounds: (i) are normally soluble in water, but insoluble in organic solvents. conduct an electric current when molten or in solution, but not in the solid. TOTAL / 17

3 TOPIC 4 Questionsheet 2 COVALENT BONDING a) What do you understand by the following terms? (i) Covalent bond Dative covalent bond b) Show, by means of dot and cross diagrams of outer electrons, the bonding present in: (i) silicon tetrafluoride, SiF 4 the ammonium ion, NH 4 + (iii) the cyanide ion, CN _ c) Give an example of a covalent compound which does not obey the octet rule of valency, and state in what respect the rule is not obeyed. d) Aluminium chloride is used as a catalyst in the chlorination of benzene, its role being to generate the electrophile Cl + : AlCl 3 + Cl 2 Cl + + AlCl 4 - What features of the AlCl 3 molecule make this reaction possible? TOTAL / 14

4 TOPIC 4 Questionsheet 3 σ AND π BONDING The carbon-carbon bond in ethane, CH 3 -CH 3, has a bond dissociation enthalpy of 348 kj mol -1, whilst that in ethene, CH 2 =CH 2, has a value of 612 kj mol -1. a) Why is the double-bond in ethene not twice as strong as the single bond in ethane?... [4] b) Show, by means of a labelled diagram, how σ and π bonds are formed in the ethene molecule. c) By reference to your answers to a) and b) above, briefly explain why ethene is more reactive than ethane, even though the carbon-carbon bond is stronger. d) In benzene, all the carbon-carbon bonds are the same length, and have a bond dissociation enthalpy of 518 kj mol -1. [3] (i) How would you expect the bond lengths in benzene to compare with those in ethane and ethene? Explain why the bond lengths in benzene are identical. TOTAL / 15

5 TOPIC 4 Questionsheet 4 SHAPES OF MOLECULES AND IONS I a) (i) Give the main features of the electron pair repulsion theory (Sidgwick-Powell theory) for predicting the shapes of molecular species. State the assumptions upon which this theory is based. b) Deduce the shapes of the following molecules, and draw clear diagrams to show the bond angles. (i) BH 3 PCl 3 (iii) SCl 2 c) (i) State the isoelectronic principle.... [1] Use this principle to deduce the shape of the sulfite ion, SO 3 2-, by comparison with the PF 3 molecule. TOTAL / 15

6 TOPIC 4 Questionsheet 5 SHAPES OF MOLECULES AND IONS II There is now a well-established chemistry of some of the noble gases. This question concerns some of these compounds. a) Give the electronic configuration of xenon (atomic number 54). b) Why is xenon able to form compounds, whereas the previous elements in this group cannot do so?... [4] c) Explain the shape of each of the folowing molecules. Write down a word (or words) to describe that shape, and draw a diagram to illustrate your answer. (i) XeF 2 Explanation and diagram Description of shape... [1] XeO 3 Explanation and diagram Description of shape... [1] (iii) XeF 6 Explanation and diagram Description of shape... [1] TOTAL / 15

7 TOPIC 4 Questionsheet 6 IONIC BONDING TENDING TOWARDS COVALENCY a) Explain the terms polarising power and polarisability as applied to cations and anions respectively, and state the factors which govern them. Polarising power of a cation... Polarisability of an anion... b) In terms of the polarising power of cations and the polarisability of anions, explain why: (i) aluminium fluoride is ionic but aluminium chloride is covalent. beryllium chloride is covalent but magnesium chloride is ionic. c) Predict, giving your reasons, the bonding you would expect in lithium iodide. d) In Group 2, barium forms a stable peroxide, BaO 2, but magnesium forms only the normal oxide. Explain this. TOTAL / 17

8 TOPIC 4 Questionsheet 7 COVALENT BONDING TENDING TOWARDS IONIC BONDING The following table gives the electronegativities of some of the elements of the Periodic Table: Li Be B C N O F Na Mg Al Si P S Cl a) What do you understand by the electronegativity of an element? b) The percentage of ionic character in a bond between two elements can be estimated from the expression % ionic character = 100 (difference in electronegativity)/3.3 Use this expression to estimate the percentage ionic character in: (i) NaCl... [1] SCl 2... [1] (iii) AlCl 3... [1] c) (i) What is meant by the term hydrolysis?... [1] The ability of a chloride to undergo hydrolysis may reflect the nature of the bonding. Illustrate this statement by referring to sodium chloride and aluminium chloride.... [4] d) What is meant by the following terms? (i) Bond dipole... Dipole moment... e) With reference to the table of electronegativities, explain why PCl 3 has a dipole moment, whereas monomeric AlCl 3 does not.... [4] TOTAL / 18

9 TOPIC 4 Questionsheet 8 METALLIC BONDING a) Describe the bonding found in metals.... [4] b) By reference to your answer to a) explain why metals: (i) generally have high melting points. conduct electricity in both solid and liquid states. (iii) are good conductors of heat. c) Sodium has a melting point of 98 o C, but magnesium melts at 650 o C. By referring to the bonding and structures in these metals, explain this difference.... [5] TOTAL / 16

10 TOPIC 4 Questionsheet 9 INTERMOLECULAR FORCES a) What forces exist between molecules of methane? How do these forces arise? b) (i) State what is meant by hydrogen bonding and explain what causes it. Draw a diagram to show hydrogen bonding in water. c) (i) When propanone, (CH 3 ) 2 CO, is mixed with trichloromethane, CHCl 3, the boiling point of the mixture is higher than might be expected. Explain this. [1] Draw a diagram to illustrate your answer. [1] d) List all the forces which exist between particles in an aqueous solution of sodium chloride. TOTAL / 14

11 TOPIC 4 Questionsheet 10 PROPERTIES AND BONDING For each of the following substances, suggest the bonding and structure that you would expect it to have. Give the key relevant reasons for your answer. a) Titanium(IV) Chloride. This is a liquid at room temperature (boiling point 137 C) which is an intermediate in the production of titanium. Bonding... [1] Structure... [1] Reasons... [1] b) Silicon Dioxide A transparent glass like substance, melting point about 1600 C, which is used in scientific equipment because it is also transparent in the infra-red and ultra-violet parts of the spectrum. It is a poor conductor of electricity as a solid or liquid. Bonding... [1] Structure... [1] Reasons... c) Titanium. This element, melting point 1675 C, is used in the manufacture of aircraft, space capsules, aeroengines and the electrodes of some electrolysis plants because of its good electrical conductivity and resistance to chemical attack. Bonding... [1] Structure... [1] Reasons... [1] d) Cryolite. This is a white crystalline solid which melts at about 1000 C. The molten solid conducts electricity, so it is used to dissolve aluminium oxide in the electrolytic process to manufacture aluminium. The solid does not conduct electricity. Bonding... [1] Structure... [1] Reasons... [1] e) Bitumen A black viscous material which is obtained as a residue from the crude oil distillation. It is used for waterproofing or, when mixed with aggregate, the construction of roads. It can be dissolved in aromatic hydrocarbon solvents such as toluene or softened by heating. Bonding... [1] Structure... [1] Reasons... [1] f) Ethane-1,2-diol This is a liquid which boils at 197 C, and is used in antifreeze in car radiators. Its aqueous solution in water is a poor conductor of electricity. Bonding... [1] Structure... [1] Reasons... [1] What does the fact that it is both soluble in water and has poor electrical conductivity tell you?... [1] Quality of language [1] TOTAL / 18

12 TOPIC 4 Questionsheet 11 CRYSTAL STRUCTURE Two of the allotropes of carbon are diamond and graphite. The former is hard, and does not conduct an electric current; the latter is softer and conducts electricity. a) Show, by means of diagrams, the lattice structures of these two allotropes. Diamond Graphite b) Explain why graphite: [4] (i) may be used as a lubricant. conducts an electric current. c) Crystals of silicon and water (ice) have similar structures to diamond. Explain why: (i) silicon is softer than diamond. ice has a much lower melting point than diamond. (iii) ice floats on water. TOTAL / 15

13 TOPIC 4 Questionsheet 12 CHANGES OF STATE a) (i) On the axes below, sketch the trend in boiling points of the noble gases. Temperature/ o C He Ne Ar Kr Xe [1] Explain the shape of this graph. b) Chlorine boils at 238 K, but the next element in the Periodic Table, argon, boils at only 87 K. Explain this. c) Strontium chloride, SrCl 2, (M r = 157) is a solid at room temperature and pressure, but carbon tetrachloride, CCl 4, (M r = 152) is a volatile liquid. Explain this. d) Complete the following table as to compare the motion and order (i.e. arrangement) of particles in the solid, liquid and gaseous states. Solid Liquid Gas Motion Order [6] TOTAL / 15

14 TOPIC 4 Questionsheet 13 BOILING POINTS OF HYDRIDES a) On the axes below, sketch the trends in boiling points of the hydrides in: (i) Group 4 (C-Pb) Group 6 (O-Po) Temperature/ o C Temperature/ o C C Si Ge Sn Pb O S Se Te Po [3] b) Explain the trends in these two groups, accounting for any differences between them.... [5] c) State and explain whether you would expect the corresponding graphs for Group 5 hydrides and Group 7 hydrides to resemble the one you have sketched for Group 4 or Group 6. d) Concerning the hydrides of Group 4; methane, CH 4, is stable as a gas well above its boiling point, but plumbane, PbH 4, cannot be obtained as a vapour at atmospheric pressure, since it decomposes before reaching its boiling point. Explain this, and suggest how plumbane might be obtained in the gaseous state. TOTAL / 14

15 TOPIC 4 Questionsheet 14 SOLUBILITY OF IONIC COMPOUNDS a) Ions in aqueous solution are said to be hydrated by ion-dipole attraction. Explain this term, and illustrate your answer by sketches for a cation and an anion. Cation Anion b) In the case of hydrated transition metal cations, H 2 O molecules are held more strongly than they would be by ion-dipole attraction alone. (i) Why is this? [5] Why is the Na + ion hydrated only by ion-dipole attraction? c) (i) Define the standard hydration enthalpy of an ion. State and explain the trend in hydration enthalpies of cations which is observed on descending Group 1. d) (i) Bearing in mind the trend in hydration enthalpies you have described in c), would you expect the solubilities of Group 1 compounds to increase or decrease on descending the group?... [1] In reality, the solubilities of some Group 1 compounds (e.g. carbonates) increase down the group, while the solubilities of others (e.g. manganates(vii)) decrease. Explain briefly the reason for this. TOTAL / 19

16 TOPIC 4 Questionsheet 15 TEST QUESTION I a) Give dot and cross diagrams to show the bonding in: (i) ammonia, NH 3 boron trifluoride, BF 3 b) Ammonia and boron trifluoride react when mixed to form a compound with the formula BF 3.NH 3. Give a diagram to show the bonding in this molecule, using the normal symbols for covalent and dative covalent bonds. c) Give and explain the molecular shape of: (i) ammonia. boron trifluoride. d) (i) What geometry would you expect around the nitrogen atom in BF 3.NH 3?... [1] Explain why the H _ N _ H bond angle in this compound differs from that in ammonia. e) How and why would you expect the F _ B _ F bond angle in BF 3.NH 3 to differ from that in boron trifluoride? TOTAL / 13

17 TOPIC 4 Questionsheet 16 TEST QUESTION II a) (i) What shape is molecular phosphorus pentachloride?... [1] How do you account for this shape? (iii) Draw a diagram to illustrate the shape of the molecule, showing the Cl _ P _ Cl bond angles. (iv) In the solid state, phosphorus pentachloride exists as [PCl 4 ] + [PCl 6 ] -. Draw these two species, including their bond angles, and describe their shapes. [PCl 4 ] + [PCl 6 ] - Shape... Shape... b) Nitrogen is unable to form a pentachloride, but does show an oxidation state of +5; for example, in the nitrate ion, NO 3-. Explain this. TOTAL / 12

18 TOPIC 4 Questionsheet 17 TEST QUESTION III Boron forms a chloride BCl 3. a) The formation of the covalent bonds with chlorine can be explained by the following sequence: A filled (A) and the sole occupied (B) combine to form three equivalent(c) which are arranged in space so as to give minimum (D) (i) Suggest terms for labels A, B, C and D: A... [1] B... [1] C... [1] D... [1] Draw a diagram to illustrate the molecule structure and name the geometry [3] (iii) Explain why the molecule is non-polar even though the B-Cl bonds are polar b) When BCl 3 reacts with ammonia this structure is formed : H 3 N:BCl 3 (i) Name the type of bond formed between the N and B atoms (1)... [1] Suggest a value for the new Cl-B-Cl bond angle (1)... [1] (iii) Explain why this structure is polar (2) TOTAL / 13