PYQ TOPIC 4: 2011/2012

(a) Draw the electron dot symbols for Cl and O atoms.

[2 marks]
(b) Draw the Lewis structures for ClO3- and ClO4- ions. State the molecular geometry and predict
the bond angles in each ion.
[8 marks]
(c) Element X and Y have proton number of 12 and 7, respectively.
(i) Write the chemical formula of the compound formed between X and Y.
(ii) Show the formation of the compound using Lewis symbol.
[3 marks]
(d) Draw all the resonance structures of nitrite ion, NO2-.
[2 marks]
(e) Based on valence shell electron pair repulsion (VSEPR) theory, describe the geometry of
methane, CH4, ammonia, NH3 and water, H2O molecules.
[20 marks]
PYQ TOPIC 4: 2012/2013
(a) For each of the molecules given; PCl3, PCl5 and POCl3,
(i) draw a Lewis structure and name the shape based on molecular geometry.
(ii) predict the bond angle and deduce the polarity.
[12 marks]
(b) Show the formation of a dative bond in the reaction of;
AlCl3 + Cl- → AlCl4-
[3 marks]
(c) By using Lewis dot symbol,
(i) show the formation of the compounds, BCl3 and LiCl, from their respective atoms.
(ii) identify the types of bond in each compound.
(iii) explain the hybridization state of the central atom in BCl3 molecule.
(iv) state the molecular geometry of BCl3 molecule.
[10 marks]
(d) Formic acid is widely used in the preservation of biological specimens. Its chemical structure
is shown below:

(i) Draw and describe the formation of bonds by involving the overlapping of orbitals.
(ii) What are the possible intermolecular forces that exist between these acid molecules?
[10 marks]
PYQ TOPIC 4: 2013/2014
(a) Ammonia, NH3, is a colourless gas with a characteristic pungent smell.
(i) Using Lewis dot symbols show the formation of ammonia from the respective
elements.
(ii) Predict the hybridisation of the central atom of ammonia and draw a diagram of the
molecule showing the overlapping of the orbitals.
(iii) Describe the polarity of the ammonia molecule.
[9 marks]
(b) Use the valence shell electron pair repulsion (VSEPR) theory to explain the difference in the
bond angles between the following pairs of compound/ion.
(i) CO2 and CO32-
(ii) PCl3 and H2O
[6 marks]
(c) CO2 and BeH2 are triatomic covalent molecules.
(i) Describe in detail the formation of the covalent bonds in these molecules.
(ii) Explain why CO2 obeys the octet rule while BeH2 does not.
[10 marks]
(d) Formal charge is a useful guide in determining the best or preferred structure. Explain this
statement using [OCN]- ion as example.
[10 marks]
PYQ TOPIC 4: 2014/2015
(a) The formula of formic acid is HCO2H. One of the carbon-oxygen bond lengths in this molecule
is 1.36 Ǻ while the other is 1.23 Ǻ. Draw the Lewis structure of this molecule and label these
bonds.
[5 marks]
(b) Xenon can be covalently bonded to fluorine and oxygen to form xenon compounds, XeF4 and
XeO2F2. For both compounds,
(i) determine the number of bonding electron pair(s) and lone electron pair(s) around the
central atom xenon.
[4 marks]
(ii) state the molecular geometry.
[2 marks]
(iii) determine the hybridisation of xenon atom.
[2 marks]
(iv) predict the polarity.
[2 marks]
(c) Draw and explain the structures of BH3, NH3 and PH3 using valence shell electron pair
repulsion theory. Also, show the overlapping of orbitals in the PH3 molecule.
The boiling points of BH3, NH3 and PH3 are 173 K, 240 K, 185 K, respectively. Explain why
the boiling point of PH3 is greater than BH3 but lower than NH3.
 [20 marks]
PYQ TOPIC 4: 2015/2016
(a) An atom X has 5 valence electrons. X reacts with fluorine gas to form XF3 and XF5
compounds. For each compound,
(i) draw the Lewis structure,
(ii) predict the electron pair geometry and the molecular geometry and
(iii) draw the molecular geometry and state the bond angle(s).
[13 marks]
(b) Predict the change in hybridization (if any) of the X atom in the following reaction:
XF3 + F2 → XF5
[2 marks]
(c) Name the bonding theory that explains orbital hybridisation.
Using orbital diagram, describe the hybridisation of the central atom in sulphur hexafluoride,
SF6 and formaldehyde, H2CO, molecules.
Draw the orbital’s overlaps of each molecule and state the expected bond angles.
[20 marks]
PYQ TOPIC 4: 2016/2017
(a) An atom X combines with oxygen atoms to form two covalent molecules, XO2 and XO3. XO2 is
identified as a polar molecule while XO3 is a nonpolar molecule.
(i) Draw a possible molecular geometry for each of the molecule.
(ii) Comment on the polarity of X-O bond. Give a possible reason.
(iii) Explain why XO2 is polar while XO3 is nonpolar.
[7 marks]
(b) Phosphoryl chloride, POCl3, can be prepared by the reaction of phosphorus trichloride, PCl 3
with oxygen at 20-50˚C.
(i) Draw the most stable Lewis structure of PCl3 and POCl3, with P as the central atom.
(ii) What is the hybrid orbital of P atom in both compounds?
(iii) Show the overlapping of orbitals in PCl3.
(iv) Compare the Cl-P-Cl bond angles in PCl3 and POCl3. Explain your answer.
[8 marks]
(c) CH3F and CF4 are tetrahedral molecules. Using the Lewis structure and dipole moment of
these molecules, deduce their polarity.
[10 marks]
(d) Iodine pentafluoride, IF5, is a colourless liquid with a pungent odour. By using VSEPR theory,
predict the geometry and bond angles of this compound.
Show how the orbitals of the central atom undergo hybridisation.
Draw a labelled diagram showing the overlapping of orbitals in the molecule.
[10 marks]
PYQ TOPIC 4: 2017/2018
(a) The azide ion, N3-, exists in several resonance forms.
(i) Draw possible resonance structures for the azide ion.
(ii) Use formal charges to select the most stable structure.
(iii) Using Lewis structure, explain why N3- ion exists, whereas trifluoride ion, F3-, does not
exist.
[9 marks]
(b) Chloroform, CHCl3, is a common organic solvent. If H in CHCl3 is replaced by Cl, it becomes
CCl4, a toxic solvent. For each of CHCl3 and CCl4 compound,
(i) Draw the molecular shape.
(ii) Show the bond polarity.
(iii) Predict the polarity.
[6 marks]
(c) Sodium bicarbonate, NaHCO3, is used in baking as a raising agent. When dissolved in water,
the salt dissociates into ions. Write the Lewis structure for the bicarbonate ion, HOCO 2-, and
draw its resonance structures.
Determine the shape of the HOCO2- ion and the hybridization of central atoms. Draw and
label the overlapping of the orbitals to show the formation of the covalent bonds.
[12 marks]
(d) Metallic compounds have some physical properties which are different from covalent
compounds. State four (4) properties and relate these properties to the metallic bonding.
[8 marks]
PYQ TOPIC 4: 2018/2019
(a) Ammonia, NH3 and boron trifluoride, BF3 are covalent compounds. NH3 and BF3 react to form
H3NBF3 molecule.
(i) Explain why NH3 obeys octet rule but BF3 does not.
(ii) Show the formation of H3NBF3 molecule using Lewis dot symbol and label the bond
formed.
[5 marks]
(b) Oxygen difluoride, OF2 is a strongly oxidising colourless gas.
(i) Determine the molecular geometry of this molecule.
(ii) Explain whether OF2 is a polar and non-polar molecule.
[8 marks]
(c) Aluminium and sodium are metals.
(i) Explain the formation of metallic bond in sodium using the electron sea model.
(ii) Why aluminium has higher boiling point than sodium?
[4 marks]
PYQ TOPIC 4: 2019/2020
(a) Explain each of the following statements
(i) Upon reaction with fluorine, oxygen forms only OF2 whereas sulphur forms SF2, SF4 and
SF6 molecules.
(ii) The shape of a PF5 molecule differs from that of an IF5 molecule.
(iii) Of the three possible resonance, structures for OCN- BELOW, III is the best structure.
[O=C=N]- [O≡C−N]- [O−C≡N]-
I II III

[10 marks]

(b) Illustrate the hybridisation of the central atom in SF 4 using orbital diagrams. Show and label
the overlapping of orbitals in the molecule.
[7 marks]
(c) Explain the difference in melting point between elements in group 1 and group 17

[5 marks]
PYQ TOPIC 4: 2020/2021
Phosgene, COCl2, is a chemical used in the production of plastics and pesticides. Given that chlorine
cannot be the central atom,
(a) draw three (3) possible structures of phosgene
[3 marks]
(b) determine the most plausible structure and give your reason
[5 marks]
(c) determine the hybrid orbital for the central atom of the most plausible structure
[4 marks]
(d) name the molecular shape and draw the overlapping orbitals of COCl2.
[5 marks]
PYQ TOPIC 4: 2021/2022
(a) Boiling points of Br2 and I2 are at 58.8˚C and 184.3˚C respectively. Explain.
[2 marks]
(b) Determine the polarity of the following molecules:
(i) CS2
(ii) SO2
(iii) NO
(iv) H2O
[12 marks]
(c) Draw all the possible structure of CNO- and determine the most plausible Lewis structure.
 [8 marks]
PYQ TOPIC 4: 2021/2022
(d) Predict the molecular geometry and bond angles of the following molecules:
(i) O3
(ii) H2S
(iii) SCl2
(iv) XeF2
[12 marks]
(e) Arrange the following compounds in the order of increasing boiling point. Explain your
answer.
HF, HCl, Cl2
[3 marks]
(f) State the hybridisation of the central atom in the following molecules:
(i) NH3
(ii) H2O
(iii) ClF3
(iv) CH3Cl
[8 marks]
(g) Deduce the molecular shape of the following species:
(i) SiCl4
(ii) SF4
(iii) XeF4
(iv) CH4
[12 marks]
PYQ TOPIC 4: 2022/2023
(a) Selenium dioxide, SeO2, is a colourless solid and one of the most available forms of
selenium.
(i) Draw the Lewis structure of SeO2.
(ii) Based on VSEPR theory, predict the molecular geometry of SeO2.
(iii) Determine hybridisation on the central atom.
(iv) Explain whether SeO2 is polar or non-polar.
[7 marks]
(b) Calcium is a silvery-white soft metal that tarnishes easily in the air.
By using the electron sea model, illustrate the formation of metallic bonds in calcium.
Explain the electrical conductivity exhibited by calcium.
[5 marks]
(c) Aluminium conducts electricity but aluminium chloride does not. Explain.
[5 marks]