Bonding (A-Level) — A-Level Chemistry Revision

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What is Bonding (A-Level)?

A-Level Chemistry expands on GCSE bonding to include a more nuanced understanding of covalent bonds in terms of orbital overlap, leading to sigma (σ) and pi (π) bonds. It introduces the concept of electronegativity and how it leads to bond polarity and intermolecular forces (van der Waals forces, permanent dipole-dipole interactions, and hydrogen bonding), which are crucial for explaining the physical properties of substances like boiling points and solubility. The shapes of simple molecules and ions are also explained using the electron pair repulsion theory (VSEPR).

Board notes: All boards require a thorough understanding of VSEPR theory to predict molecular shapes. AQA often asks students to draw and name a wide variety of molecular shapes. Edexcel places emphasis on the link between bonding, structure, and physical properties. OCR may ask more comparative questions, requiring students to explain differences in properties between substances based on their bonding and intermolecular forces.

Worked example

Common mistakes

• 1Confusing intermolecular forces with intramolecular bonds. Covalent bonds within a molecule are much stronger than the intermolecular forces between molecules.
• 2Incorrectly identifying the type of intermolecular force. For example, stating that methane has hydrogen bonds (it only has weak van der Waals forces) or that all molecules with polar bonds are polar molecules (symmetrical molecules like CCl4 are non-polar overall).
• 3Drawing dot-and-cross diagrams that don't account for the correct number of outer shell electrons or the overall charge on an ion.

Bonding (A-Level) exam questions

Exam-style questions for Bonding (A-Level) with mark-scheme style solutions and timing practice. Aligned to AQA, Edexcel and OCR specifications.

Frequently asked questions

• What is a dative covalent bond?

  A dative (or coordinate) bond is a covalent bond in which both electrons in the shared pair come from the same atom. This occurs when one atom has a lone pair of electrons and another has an empty orbital, such as in the formation of the ammonium ion (NH4+).

• Why is the boiling point of water much higher than that of hydrogen sulfide (H2S)?

  Water has strong hydrogen bonds between its molecules due to the high electronegativity difference between oxygen and hydrogen. H2S has a smaller electronegativity difference and only has weaker permanent dipole-dipole forces and van der Waals forces, which require less energy to overcome.