Checklist

Here is a comprehensive, highly detailed revision checklist for Cambridge 9701 A Level Chemistry: Chapter 3 - Chemical Bonding.

I have meticulously extracted the syllabus requirements and expanded upon them by cross-referencing every single past paper question, mark scheme, and examiner report from the documents provided (spanning 2009 to 2025).

This is formatted as a Markdown file, perfectly structured for Obsidian. You can paste this directly into a new note. Use the checkboxes to track your mastery.

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📝 9701 AS Chemistry Checklist: 3. Chemical Bonding

How to use this checklist

As an expert examiner, I can tell you that the difference between a B and an A* in this chapter lies in precision of language. Knowing a concept isn’t enough; you must write the exact keywords the mark scheme demands. Pay special attention to the Examiner Tips—these are direct observations of where thousands of candidates have lost marks in past papers.

3.1 & 3.6 Electronegativity & Bond Polarity

• Define Electronegativity: I can define it exactly as “the power of an atom to attract electrons to itself (in a covalent bond).”
• Explain Trends: I can explain why electronegativity increases across a period (increasing nuclear charge, similar shielding) and decreases down a group (increasing atomic radius/shielding).
• Define Bond Polarity: I can describe it as the asymmetric distribution of electron density between two bonded atoms due to a difference in electronegativity.
• Predict Bond Types: I can use Pauling electronegativity values to predict whether a bond will be non-polar covalent, polar covalent, or ionic.
• Dipole Moments: I can determine if a whole molecule has an overall dipole moment based on its shape (e.g., has no overall dipole because individual dipoles cancel out, but does).

3.2 Ionic Bonding

• Definition: I can define ionic bonding as the “electrostatic attraction between oppositely charged ions.”
• Dot-and-Cross Diagrams: I can draw accurate dot-and-cross diagrams for ionic compounds (e.g., ).
  • Examiner Tip: Always include square brackets around the ions and place the charge outside the bracket. Remember that the metal ion usually has an empty outer shell in the diagram.
• Physical Properties: I can explain why ionic compounds have high melting points (strong electrostatic attraction requires a lot of energy to overcome).
• Conductivity: I can explain that ionic compounds conduct electricity only when molten or aqueous because the ions are mobile/free to move.
  • Examiner Tip: NEVER use the phrase “delocalised electrons” or “free electrons” when discussing ionic conductivity. You will lose the mark instantly.

3.3 Metallic Bonding

• Definition: I can define metallic bonding as the “electrostatic attraction between positive metal ions and delocalised electrons.”
• Diagrammatic Representation: I can draw a labelled diagram of a metallic lattice.
  • Examiner Tip: You must draw at least two rows of positive ions. Label the circles as “positive metal ions/cations” (NOT nuclei or protons) and the spaces between as “delocalised electrons.”
• Melting Point Trends: I can explain why melting points increase from to (greater nuclear charge, smaller ionic radius, and more delocalised electrons per atom lead to stronger electrostatic attraction).
• Conductivity: I can explain that metals conduct electricity because delocalised electrons are mobile.

3.4 Covalent and Coordinate (Dative) Bonding

• Definition: I can define a covalent bond as the “electrostatic attraction between the nuclei of two atoms and a shared pair of electrons.”
• Sigma () vs Pi () Bonds:
  • I can describe a bond as the direct/head-on overlap of orbitals.
  • I can describe a bond as the sideways overlap of adjacent p-orbitals (above and below the plane).
  • I can draw diagrams showing the formation of both and bonds.
  • Examiner Tip: In addition reactions, the bond breaks because the electrons are further from the nuclei and experience weaker electrostatic attraction, making them more susceptible to electrophilic attack.
• Coordinate (Dative) Bonding:
  • I can define a coordinate bond as a covalent bond where both electrons in the shared pair come from the same atom.
  • I can draw structures showing dative bonds with an arrow pointing from the donor to the acceptor (e.g., ).
• Bond Energy and Reactivity: I can relate bond energy to reactivity (e.g., is highly unreactive because of its very high bond energy/strong triple bond; is more reactive than because bonds are weaker).
• Octet Expansion: I can explain that Period 3 elements (like P, S, Cl) can expand their octet because they have accessible 3d-orbitals.

3.5 Shapes of Molecules & VSEPR Theory

• VSEPR Principle: I can state that electron pairs repel each other to be as far apart as possible, and the order of repulsion is: Lone Pair-Lone Pair > Lone Pair-Bonding Pair > Bonding Pair-Bonding Pair.
• I have memorised the exact bond angles and names of the following standard shapes:
  • Linear () e.g.,
  • Trigonal Planar () e.g.,
  • Tetrahedral () e.g.,
  • Trigonal Bipyramidal ( and ) e.g.,
  • Octahedral () e.g.,
• I can deduce the shape and angle of derivatives with lone pairs:
  • Pyramidal () e.g., (1 lone pair, 3 bonding pairs)
  • Non-linear / V-shaped / Bent () e.g., (2 lone pairs, 2 bonding pairs)
• Hybridisation: I can correctly identify the hybridisation of atoms in organic and inorganic molecules:
  • : 4 sigma bonds (e.g., alkanes)
  • : 3 sigma bonds, 1 pi bond (e.g., alkenes, carbonyls)
  • : 2 sigma bonds, 2 pi bonds (e.g., alkynes, nitriles, )

3.6 Intermolecular Forces (IMFs) & Physical Properties

Examiner Tip: Melting and Boiling Points

The most common error in Paper 2 is confusing what breaks when a substance melts.

• Melting Giant Covalent structures (): Breaks strong covalent bonds.
• Melting Simple Molecular structures (): Breaks WEAK intermolecular forces (London forces, pd-pd, or H-bonds), NOT covalent bonds.

• Instantaneous Dipole - Induced Dipole (London/Dispersion) Forces:
  • I can explain that id-id forces increase in strength as the number of electrons in the molecule increases.
  • I can use this to explain trends (e.g., boiling point of halogens: ; or Group 16 hydrides ; or because has more electrons).
• Permanent Dipole - Permanent Dipole (pd-pd) Forces:
  • I can identify molecules that possess pd-pd forces (asymmetrical polar molecules).
• Hydrogen Bonding:
  • I know the strict criteria: a Hydrogen atom covalently bonded to a highly electronegative atom (N, O, or F) interacting with a lone pair on another N, O, or F.
  • Drawing H-bonds: I can draw a perfect H-bond between two molecules (e.g., , Lactic Acid).
  • Examiner Tip for Drawings: You MUST include (1) Relevant lone pairs, (2) all relevant partial charges ( and ), and (3) a dashed line showing the H-bond originating directly from the lone pair to the .
• Anomalous Properties of Water:
  • I can explain why ice is less dense than water (H-bonds hold molecules in an open lattice structure with more empty space).
  • I can explain its relatively high melting/boiling point and surface tension compared to other Group 16 hydrides (due to strong hydrogen bonds requiring significant energy to overcome).
• I can compare the thermal stability of Hydrogen Halides ( to ) and explain that stability decreases down the group because the atomic radius of the halogen increases, making the bond longer and weaker (less orbital overlap). Note: Thermal stability relies on covalent bond strength, NOT intermolecular forces!

3.7 Master List of Highly-Tested Dot-and-Cross Diagrams

I have practiced drawing dot-and-cross diagrams (showing outer electrons only) for the following exact molecules that have appeared in past papers:

• (Triple bond, one lone pair on each N)
• (Triple bond consisting of 2 normal covalent and 1 dative bond from O to C. Lone pair on C and O).
• (Linear, double bonds, similar to )
• (V-shaped, 2 bonding pairs, 2 lone pairs on S, full octets on Cl)
• (Expanded octet on P: double bond to O, single bonds to 3 Cls. 10 electrons around P)
• (Dimer: Two molecules joined by two dative bonds from the Cl lone pairs of one molecule to the empty orbital of the Al on the other)
• (Must show the covalent/dative bonds in inside a bracket with a charge, and in a separate bracket with 8 crosses/dots and a charge).
• (Double bond between N=N, single bonds to F. One lone pair on each N).
• (Can be drawn with one double bond and one dative bond, OR two double bonds with an expanded octet. Both are accepted, but ensure S has a lone pair).

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Final Self-Reflection for Chapter 3:

• Have I stopped using the phrase “free electrons” and replaced it with “delocalised electrons” or “mobile ions” depending on the context?
• Do I always check if a question is asking about breaking a bond (intramolecular) vs an intermolecular force?