JPJC 2026 Chemical Bonding Revision

© Jurong Pioneer Junior College 1 Topic 3: Chemical Bonding (Foundation Kit) JURONG PIONEER JUNIOR COLLEGE Topical Revision for Physical Chemistry (Topic 3: Chemical Bonding) FOUNDATION KIT 1 [PJC MYE 2010/P1/Q9] In which one of the following pairs do the molecules have similar shapes? A AlCl3 and SO3 B AlCl3 and PCl3 C BF3 and NH3 D CO2 and SO2 2 In this question, the methyl group, CH3, is represented by Me. Trimethylamine, Me3N, reacts with boron trifluoride, BF 3, to form a compound of formula Me3N.BF3. Assume that Me3N reacts in a similar manner to NH3. How may this reaction be written in terms of the shapes of the reactants and products? A B C D

© Jurong Pioneer Junior College 2 Topic 3: Chemical Bonding (Foundation Kit) 3 Propenonitrile (acrylonitrile), CH2CHCN is a chemical used to make polymers. The structure of the compound is shown below. What is the number of  and  bonds present in the molecule?   A 4 5 B 6 2 C 6 3 D 7 2 4 [PJC MYE 2010/P1/Q11] What is the correct descending order of bond angles α, β and γ in the molecule shown below? A α > β > γ B γ > β > α C β > α > γ D γ = α > β 5 [PJC MYE 2013/P1/Q9] The characteristic smell o f garlic is due to alliin. When garlic is cut an enzyme releases alliin because alliin has the right shape to fit the enzyme molecules. C C CH2 H H H S O CH2 C NH2 H CO2H y z x Alliin What would you expect the bond angles x, y and z to be, to the nearest 10 degrees, in the molecule of alliin? x y z A 120  110  110  B 120  120  110  C 180  90  90  D 180  110  110  H H H O H C O C H α β γ N

© Jurong Pioneer Junior College 3 Topic 3: Chemical Bonding (Foundation Kit) 6 [PJC MYE 2012/P1/Q11] Predict the most likely bond angle at each nitrogen atom in di−imine, HN=NH. A 107 o B 118 o C 120 o D 180 o 7 [PJC MYE 2010/P1/Q18] In the gas phase, aluminium chloride is the dimer, Al2Cl6. By using this information, which of the following are structural features of the Al2Cl6 molecule? 1 Each aluminium atom is surrounded by four chlorine atoms. 2 There are twelve non-bonded electron pairs in the molecule. 3 Each aluminium atom contributes electrons to four covalent bonds. A 1, 2 and 3 are correct B 1 and 2 are correct C 2 and 3 are correct D 1 only is correct 8 [AJC Promo 2016/P1/Q8-modified] Molecular dimerisation can be described as the process in which two identical molecules combine to give a single product. Examples of dimers are: Al2Cl6, N2O4 and (CH3CO2H)2. Which of the following descriptions about the above dimers is incorrect? A Al2Cl6 is a planar molecule. B N2O4 is formed through the dimerisation of two NO2 molecules via the formation of a N−N covalent bond. C Each aluminium atom is surrounded by four chlorine atoms in Al2Cl6. D Hydrogen bonds hold the CH3CO2H molecules together in the dimer. 9 [PJC MYE 2013/P1/Q18] Which statements concerning the lattice structures of graphite and diamond are correct? 1 The C−C−C bond angle between nearest neighbours is smaller in diamond than in graphite. 2 The shortest carbon−carbon bond occurs in diamond. 3 All covalent bonds in diamond are of the same strength but those in graphite are not. A 1, 2 and 3 are correct B 1 and 2 are correct C 2 and 3 are correct D 1 only is correct

© Jurong Pioneer Junior College 4 Topic 3: Chemical Bonding (Foundation Kit) 10 [PJC MYE 2010/P1/Q8] Silicon carbide (carborundum) is a shiny, hard, chemically inert material with a very high melting point. It can be used to sharpen knives and make crucibles. What type of structure explains these properties? A a giant structure with covalent bonds between silicon and carbon atoms. B a giant structure containing metallic bonding. C a giant layer structure with covalent bonds between atoms and instantaneous dipole -induced dipole forces between the layers. D a simple molecular structure with covalent bonds between atoms of silicon and carbon. 11 [PJC MYE 2012/P1/Q10] The gecko, a small lizard, can climb up a smooth glass window. The gecko has millions of microscopic hairs on its toes and each hair has thousands of pads at its tip. The result is that the molecules in the pads are extremely close to the glass surface on which the gecko is climbing. What is the attraction between the gecko’s toe pads and the glass surface? A co−ordinate bonds B ionic bonds C covalent bonds D instantaneous dipole−induced dipole force 12 [PJC MYE 2012/P1/Q12] Consider the following four compounds. 1 (CH3)3CH 2 CH3CH2CH2CH3 3 CH3CH2CO2H 4 CH3CH2CH2Cl What is the order of decreasing boiling point of the compounds? A 4 → 3 → 2 → 1 B 4 → 3 → 1 → 2 C 3 → 4 → 2 → 1 D 3 → 4 → 1 → 2 13 Which of the following explains why carbon dioxide is a gas at room temperature while silicon dioxide is a solid? A carbon-oxygen bonds are less polar than silicon-oxygen bonds. B carbon dioxide contains double covalent bonds while silicon dioxide contains single covalent bonds. C the relative molecular mass of carbon dioxide is less than that of silicon dioxide. D instantaneous dipole -induced dipole attractions are much weaker than covalent bonds.

© Jurong Pioneer Junior College 5 Topic 3: Chemical Bonding (Foundation Kit) 14 The boiling point of water (100 oC) is greater than that of HF (20 oC). Which statement is a correct explanation of this? A Each hydrogen bond formed between water molecules is stronger than that formed between HF molecules. B There are more atoms in a water molecule than there are in an HF molecule, so instantaneous dipole induced dipole attractions are stronger in water. C There are, on average, more hydrogen bonds between water molecules than there are between HF molecules. D The water molecules have a greater permanent dipole than the HF molecule. 15 The physical properties of three substances D, E and F are shown below. Compound D E F Melting point/ C 1380 700 −120 Boiling point/ C 2300 1310 −85.1 Conductivity (solid state) poor poor poor Conductivity (molten/ liquid state) good good poor Solubility in water good good soluble What might be the identities of D, E and F? D E F 1 MgF2 KBr NH3 2 MgF2 NaF CH4 3 KBr MgF2 HF A 1, 2 and 3 B 1 and 2 only C 1 only D 2 only

© Jurong Pioneer Junior College 6 Topic 3: Chemical Bonding (Foundation Kit) 16 [PJC Promos 2010/P2/Q3(a)] The table below gives some data on selected straight-chain alkanes. number of carbon atoms molecular formula boiling point / oC 1 CH4 −161 3 C3H8 −42 8 C8H18 126 15 C15H32 271 20 C20H42 344 Explain, in terms of structure and bonding, the increasing trend in boiling points as shown by the data. 17 (a) [PJC Promos 2010/P2/Q7(b)] Explain the following observations. (i) The nitronium ion, NO2+, is linear while the nitrite ion, NO2–, is bent. Using dot–and–cross diagrams, explain the observation. (ii) Aluminium fluoride, A lF3, and aluminium chloride, A lCl3, differ markedly in their physical properties. Explain why this is so. Compound AlF3 AlCl3 Melting point / oC 1291 192 18 [PJC MYE 2010/P2/Q4(a)] (a) Halogens are highly reactive and can be harmful or lethal to biological organisms in sufficient quantities. The table below gives the boiling points of three different halogens. Elements Boiling points / °C Cl2 Br2 I2 – 35 + 59 + 184 (i) Describe and explain the variation in the volatility of the halogens. (ii) Despite having similar relative molecular masses, the boiling point of propane−1,3−diol, CH2(OH)CH2CH2OH, is much higher (210 oC) than that of chlorine. Using structure and bonding, explain the above observation. (b) In the food industry, acetic acid is used as a food additive, an acidity regulator and a condiment. In the