NJC 5T Chemical Bonding Tutorial Student

National Junior College SH1 H1 Chemistry 1 CHEMICAL BONDING TUTORIAL Interatomic Bonding 1 Using the list below, give one example to each of the following solid lattices showing the given properties. Name the structure and type of bonding found in each lattice. graphite, diamond, copper, iodine, sodium chloride (a) A hard and brittle solid. (b) A solid that conducts electricity and melts at 1085 C. (c) A solid that cuts through metal and does not conduct electricity. (d) A substance that sublimates when heated. (e) A solid that can be used as a lubricant. 2 Which statement(s) are correct? I HCl (g) can conduct electricity. II Covalent bond is a weak bond compared to ionic bond as boiling point of H2O is lower than that of MgO. III Ionic bonds and covalent bonds can both occur in the same compound. IV Metals can be distinguished from ionic compounds by their electrical conductivity in the solid and liquid state. A Statements I and III are correct. B Statements II and IV are correct. C Statement III and IV are correct. D Statements I, III and IV are correct 3 Boron trifluoride and ammonia reacts in a 1:1 mole ratio to form a single compound. Describe the type of bond formed during this reaction. 4 Explain the following observations in terms of structure and bonding. i. MgO has a higher melting point than NaCl. ii. At room temperature and pressure, CO 2 is a gas, while SiO2 is a solid of high melting temperature.

National Junior College SH1 H1 Chemistry 2 Dot-and-Cross Diagram and VSEPR 5 Fill up the table below for the following compounds: compound ‘dot-and-cross’ diagram (i) Draw and name the shape of the covalent molecule or polyatomic ion (ii) Indicate the bond angle in the diagram Bonds or intermolecular forces broken during melting or boiling process (i) Al2O3 (m.p. 2072C) Ionic compound Ionic bond (ii) AlCl3 (m.p. 192C) Covalent molecule Weak intermolecular forces (iii) PCl3 (l) (iv) CH2Cl2(l) (v) PCl5(s) (vi) HCN

National Junior College SH1 H1 Chemistry 3 compound ‘dot-and-cross’ diagram (i) Draw and name the shape of the covalent molecule or polyatomic ion (ii) Indicate the bond angle in the diagram Bonds or intermolecular forces broken during melting or boiling process (vii) SO2 (viii) SO3 (ix) H2O2 (H-O-O-H arrangement) (x) (NH4)2SO4 Ionic bond

National Junior College SH1 H1 Chemistry 4 6 A stable molecule containing atoms of the elements, X, Y and Z has the following structure. Which option is a possible combination of the elements? X Y Z A N P Cl B O S Cl C B N H D P O F 7 MTBE is a constituent of petrol. What are the values of angle P and angle Q in a molecule of MTBE? angle P angle Q A 90o 105o B 90o 180o C 109o 105o D 109o 180o 8 Using VSEPR theory, predict which compound in each of the following pair of molecules has a larger bond angle. (a) BCl3 and NCl3 (b) H2S and PH3 9 [N10/III/4c] (a) Draw ‘dot-and-cross’ diagrams to show the bonding in the molecules of NO2, O3 and BF3. In the molecule NO 2, the central atom is nitrogen. In each case you should distinguish carefully between electrons originating from the central atom and those from the two outermost atoms. Include all lone pairs in your diagrams. (b) Suggest a value for the bond angles in each of the three molecules, giving reasons for your choice. Polarity and Intermolecular Forces 10 (a) Classify the following molecules as polar or non-polar. NH3, SF6, CH2=CH2, CH3OH, ClF3, CH3OCH3 (b) Hence, classify the molecules in (a) according to the main type of intermolecular forces present. X Y X Y X Y Z Z Z Z Z Z C CH3 H3C O CH3 CH3 angle Q MTBE angle P

National Junior College SH1 H1 Chemistry 5 Structure and Physical Properties 11 The boiling points of four compounds are given in the table below. Explain the differences in boiling point between Compound Boiling point/ °C H2O 100 CH3OH 65 SiH4 –107 CH4 −164 (a) CH4 and SiH4 (b) H2O and CH3OH 12 The boiling points of three organic compounds are given in the table below. Compound Molecular formula Mr Boiling point/oC A CH3CH2OCH2CH3 74 35 B CH3CH2CH2CH2OH 74 118 C (CH3)3COH 74 83 Explain the differences in boiling point between (a) A and B (b) B and C 13 Referring to table in question 5, explain the following observations. (i) Al2O3 conducts electricity in molten state while AlCl3 in molten state does not. (ii) Difference in physical state of PCl3 and PCl5. 14 (a) The boiling point of cis-dichloroethene is 333 K, whereas that of trans-dichloroethene is 321 K. cis-dichloroethene trans-dichloroethene (b) The boiling point of R is higher than Q. C C Cl H Cl H C C Cl H H Cl C C COOH H COOH H C C COOH H H COOH Q R

National Junior College SH1 H1 Chemistry 6 Solubility 15 Predict with explanations whether or not (a) CH3CH2OH is soluble in H2O (b) NH4NO3 is soluble in benzene, C6H6. 16 Ammonia and hydrogen chloride gases are soluble in water because they interact with the solvent. HCl(g) + aq → H+ (aq) + Cl− (aq) NH3(g) + aq → NH3 (aq) Use suitable diagrams to illustrate all the possible interactions between the dissolved gas and a water molecule. Application questions 17 Provide an explanation for the following observations. (a) Ice is less dense than water. (b) The relative molecular mass of ethanoic acid is 120 in benzene, C6H6. 18 Vaporization occurs when some molecules in a liquid possesses enough kinetic energy to escape from the surface of the liquid at a given temperature. Saturated vapour pressure is the pressure on the walls of the container exerted by the gas molecules vaporized from the surface of the liquid in a closed container when the rates of condensation and evaporation are equal. Boiling occurs when the vapour pressure is equal to the external pressure which is usually the atmospheric pressure (101 kPa). The graph below shows the vapour pressures of three liquids at varying temperatures. (a) The identities for liquids A and B could be ethanol (CH3CH2OH) and propanone (CH3COCH3). Based on the graph, identify liquids A and B and explain your reasoning. [4] (b) Suggest a possible identity for C.