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HIGHER CHEMISTRY REVISION .

HIGHER CHEMISTRY REVISION . Unit 1:- Bonding, Structure and Properties. 1. Although propane and ethanol have similar molecular masses, the alkane is a gas at room temperature while the ethanol is a liquid. This difference in boiling point is due to the different strengths of the

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HIGHER CHEMISTRY REVISION .

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  1. HIGHER CHEMISTRY REVISION. Unit 1:- Bonding, Structure and Properties 1. Although propane and ethanol have similar molecular masses, the alkane is a gas at room temperature while the ethanol is a liquid. This difference in boiling point is due to the different strengths of the intermolecular forces in the two compounds. Explain why propane is a gas at room temperature while ethanol is a liquid. In your answer you should name the intermolecular forces involved in each compound and explain how they arise. 1. In propane there are only weak van der Waals attractions between the non-polar propane molecules. It takes very little energy to break these van der Waals attractions and so propane has a low boiling point. In ethanol there is a polar O-H group. The oxygen atom has a higher electronegativity (attraction for electrons) than the hydrogen . This results in the shared electrons in the O to H bond being attracted towards the oxygen giving it a slight negative charge. The hydrogen has a slight positive charge. There is an attraction between the opposite charges in neighbouring molecules which means more energy – this is known as hydrogen bonding.

  2. 2. The first twenty elements can be arranged according to bonding and structure. aluminium boron chlorine hydrogen phosphorus silicon (a) Identify the element which is a discrete molecular solid at room temperature and pressure. (b) Identify the two elements which combine to form the compound with the most covalent character. (You may wish to use page 10 of the data booklet.) 2. (a) Phosphorus. (b) Phosphorus and hydrogen. (they have the same electronegativity) 3. SiO2 3. Compounds can have different structures and properties. NH4NO3 BaSO4 Na2CO3 SiO2 K2O P2O5 Identify the compound with a covalent network structure.

  3. 4. Hydrogen sulphide, H2S, is an unpleasant gas produced when eggs rot. (a) The gas can be prepared by the reaction of iron(II) sulphide with dilute hydrochloric acid. Iron(II) chloride is the other product of the reaction. Write a balanced chemical equation for this reaction. (b) Iron metal is often an impurity in iron(II) sulphide. Name the other product which would be formed in the reaction with dilute hydrochloric acid if iron metal is present as an impurity. 5. The properties of substances depends on their structures and bonding. hydrogen phosphorus sodium lithium hydride hydrogen fluoride hydrogen iodide (a) Identify the substance with hydrogen bonding between the molecules. (b) Identify the two substances with pure covalent bonding in the molecules. 4. (a) FeS + 2HCl  FeCl2 + H2S (b) Hydrogen. 5. (a) Hydrogen fluoride. (b) Hydrogen and phosphorus.

  4. 6. • Van der Waals forces. • Hydrogen fluoride is a highly polar molecule. Fluorine atoms have a higher electronegativity (attraction for shared electrons) than hydrogen atoms. In the H-F bond the fluorine atoms have slight negative charge and the hydrogen atoms a slight positive charge. These charges result in neighbouring molecules be attracted to each other by hydrogen bonds to form double and triple molecules. • In F2 and H2 molecules the molecules a non-polar and so there is only the weak van der Waals attraction which is not strong enough to form double and triple molecules. A mass spectrometer is an instrument that can be used to gain information about the masses of molecules. When hydrogen fluoride is analysed in a mass spectrometer as well as molecules with a relative molecular mass of 20, some “double molecules” (relative molecular mass 40) and “triple molecules” (relative molecular mass 60) are found to exist. No such molecules are found when the elements hydrogen and fluorine, are separately analysed. (a) Name the weak force of attraction between molecules that is found in both liquid hydrogen and liquid fluorine. (b) Why are “double” and “triple” molecules found in hydrogen fluoride but not in hydrogen and fluorine? 6.

  5. Type B Type E Type C Type D Type A 7. Name the structure and type of bonding in silicon dioxide. Covalent network. 8. • Which type of element A to E shown above is • Monatomic gases? • Covalent network solids? • Diatomic covalent gases? • Discrete covalent molecular solids? • Metallic lattice solids? • Type E • Type B • Type D • Type C • (e) Type A

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