2 HIGHER CHEMISTRY REVISION. Unit 1:- Bonding, Structure and Properties1. Although propane and ethanol have similar molecular masses, the alkaneis a gas at room temperature while the ethanol is a liquid. Thisdifference in boiling point is due to the different strengths of theintermolecular forces in the two compounds.Explain why propane is a gas at room temperature while ethanol is aliquid.In your answer you should name the intermolecular forces involved ineach compound and explain how they arise.1. In propane there are only weak van der Waals attractions betweenthe non-polar propane molecules. It takes very little energy tobreak these van der Waals attractions and so propane has a lowboiling point.In ethanol there is a polar O-H group. The oxygen atom has ahigher electronegativity (attraction for electrons) than thehydrogen . This results in the shared electrons in the O to H bondbeing attracted towards the oxygen giving it a slight negativecharge. The hydrogen has a slight positive charge. There is anattraction between the opposite charges in neighbouring moleculeswhich means more energy
3 2. The first twenty elements can be arranged according to bonding and structure.aluminium boron chlorinehydrogen phosphorus silicon(a) Identify the element which is a discrete molecular solid at roomtemperature and pressure.(b) Identify the two elements which combine to form the compound withthe most covalent character.(You may wish to use page 10 of the data booklet.)2. (a) Phosphorus.(b) Phosphorus and hydrogen.3. SiO23. Compounds can have different structures and properties.NH4NO BaSO Na2CO3SiO2 K2O P2O5Identify the compound with a covalent network structure.
4 (a) The gas can be prepared by the reaction of iron(II) sulphide with 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 withdilute 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 withdilute hydrochloric acid if iron metal is present as an impurity.5. The properties of substances depends on their structures and bonding.hydrogen phosphorus sodiumlithium hydride hydrogen fluoride hydrogen iodide(a) Identify the substance with hydrogen bonding between themolecules.(b) Identify the two substances with pure covalent bonding in the4. (a) FeS + 2HCl FeCl2 + H2S(b) Hydrogen.5. (a) Hydrogen fluoride.(b) Hydrogen and phosphorus.
5 6.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 inboth liquid hydrogen and liquid fluorine.(b) Why are “double” and “triple” molecules found in hydrogen fluoride butnot in hydrogen and fluorine?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 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.6.
6 8. 7. Name the structure and type of bonding in silicon dioxide. Covalent network.8.Type AType CType DType EType BWhich type of element A to E shown above isMonatomic gases?Covalent network solids?Diatomic covalent gases?Discrete covalent molecular solids?Metallic lattice solids?Type EType BType DType C(e) Type A