Edexcel International A Level Chemistry
Edexcel International A Level Chemistry Covalent Bonding Exam Questions
Free Edexcel International A Level Chemistry exam questions for Covalent Bonding, with a mark scheme for every pack. Covers shared electron pairs, dot-and-cross diagrams, dative covalent bonds, sigma and pi bonds, bond length and strength, electronegativity and bond polarity.
Covalent Bonding exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About Edexcel International A Level Chemistry Covalent Bonding
Covalent bonding is a core Unit 1 topic in Edexcel International A Level Chemistry. It defines a covalent bond as the strong electrostatic attraction between two nuclei and the shared pair of electrons between them, then extends this to dative covalent bonds, multiple bonds and the sigma and pi model. You also link electronegativity to bond polarity, which explains whether a molecule is polar and prepares you for Intermolecular forces in Unit 2. Examiners frequently ask for definitions, dot-and-cross diagrams including dative bonds, comparisons of bond length and bond enthalpy, and explanations of why a molecule with polar bonds can still be non-polar overall.
What you need to know
- Definition A covalent bond is the strong electrostatic attraction between two nuclei and the shared pair of electrons between them. Evidence comes from electron density maps showing high density between bonded nuclei.
- Dot-and-cross diagrams Show all outer shell electrons, including lone pairs. Learn examples such as H2O, NH3, CO2, N2 and molecules that do not obey the octet rule, such as BF3 and SF6.
- Dative covalent bonds Both shared electrons come from the same atom, for example in NH4+ (lone pair from N to H+) and in Al2Cl6. A dative bond is shown with an arrow from the donor atom.
- Sigma and pi bonds A sigma bond forms from direct overlap of orbitals along the line between nuclei. A pi bond forms from sideways overlap of p orbitals above and below that line, so a double bond is one sigma and one pi bond.
- Bond length and strength Greater electron density between the nuclei gives a shorter and stronger bond, so C=C is shorter and stronger than C to C, though less than twice as strong.
- Electronegativity and polarity Electronegativity is the ability of an atom to attract the bonding pair of electrons in a covalent bond. A difference in electronegativity gives a polar bond with partial charges. Large differences lead towards ionic bonding.
- Polar molecules A molecule is polar if it has polar bonds and its shape means the dipoles do not cancel. CO2 and CCl4 are non-polar because they are symmetrical, while H2O and NH3 are polar.
Common mistakes in Covalent Bonding
- Defining a covalent bond as just a shared pair of electrons. The definition needs the electrostatic attraction between the nuclei and the shared pair.
- Missing lone pairs in dot-and-cross diagrams, especially on oxygen, nitrogen and the halogens.
- Saying a double bond is twice as strong as a single bond. The pi bond is weaker than the sigma bond, so a double bond is less than twice as strong.
- Concluding a molecule is polar just because it contains polar bonds. You must consider the shape and whether the dipoles cancel.
- Defining electronegativity as the ability to attract electrons in general. It is specifically the attraction for the bonding pair of electrons in a covalent bond.
Try three Covalent Bonding exam-style questions
1. Define the term covalent bond. (2 marks)
Show the mark scheme answer
Strong electrostatic attraction; between two nuclei and a shared pair of electrons.
2. Draw a dot-and-cross diagram for the ammonium ion, NH4+, and explain how the dative bond forms. (3 marks)
Show the mark scheme answer
Diagram shows N with four bonding pairs, one pair from N only, overall charge shown with square brackets and +; the nitrogen lone pair in NH3 is donated to an H+ ion; both electrons in that bond come from nitrogen.
3. Explain why tetrachloromethane, CCl4, has polar bonds but is a non-polar molecule. (2 marks)
Show the mark scheme answer
Chlorine is more electronegative than carbon so each C to Cl bond is polar; the molecule is tetrahedral and symmetrical so the bond dipoles cancel.
Covalent Bonding FAQs
What does Edexcel International A Level Chemistry Covalent bonding cover?
It covers the nature of covalent and dative covalent bonds, dot-and-cross diagrams, sigma and pi bonds, bond length and strength, electronegativity and polarity of bonds and molecules.
Which unit is Covalent bonding examined in?
Covalent bonding is part of Unit 1, and the ideas are needed again for intermolecular forces in Unit 2 and for complex ions in Unit 5.
Which dot-and-cross diagrams should I learn?
Learn simple molecules such as H2O, NH3, CH4, CO2 and N2, ions such as NH4+ and H3O+, electron deficient BF3, expanded octet SF6 and the dimer Al2Cl6.
