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S1.1 - Introduction to the particulate nature of matter S1.2 - The nuclear atom S1.3 - Electron configurations S1.4 - Counting particles by mass - The mole S1.5 - Ideal gases S2.1 - The ionic model S2.2 - The covalent model S2.3 - The metallic model S2.4 - From models to materials S3.1 - The periodic table - Classification of elements S3.2 - Functional groups - Classification of organic compounds R1.1 - Measuring enthalpy changes R1.2 - Energy cycles in reactions R1.3 - Energy from fuels R1.4 - Entropy and spontaneity AHL R2.1 - How much? The amount of chemical change R2.2 - How fast? The rate of chemical change R2.3 - How far? The extent of chemical change R3.1 - Proton transfer reactions R3.2 - Electron transfer reactions R3.3 - Electron sharing reactions R3.4 - Electron-pair sharing reactions

S2.2 - The covalent model

2.2.1 Covalent Bonds and Lewis Formulas 2.2.2 Bond Types 2.2.3 Co-coordination (Dative) Bonds 2.2.4 VSEPR Shapes of Molecules 2.2.5 Electronegativity and Bond Polarity 2.2.6 Polarity and Dipole Moments 2.2.7 Covalent Network Structures and Allotropes 2.2.8 Intermolecular Forces 2.2.9 Physical Properties of Covalent Substances 2.2.10 Chromatography and Intermolecular Forces 2.2.11 Resonance Structures (AHL) 2.2.12 Benzene and Resonance (AHL) 2.2.13 Expanded Octet and VSEPR (AHL) 2.2.14 Formal Charge (AHL) 2.2.15 Sigma and Pi Bonds (AHL) 2.2.16 Hybridization (AHL)

Chromatography and Intermolecular Forces

Specification Reference S2.2.10

Quick Notes

  • Chromatography separates mixtures based on the relative attraction of substances to:
    • The mobile phase (moves through the system)
    • The stationary phase (does not move)
  • Separation depends on intermolecular forces (e.g. polarity, hydrogen bonding, dispersion forces).
  • The more strongly a substance interacts with the mobile phase, the further it moves.
  • The retardation factor (Rf) is calculated as:
    Rf = distance moved by substance ÷ distance moved by solvent front
    • Rf values are between 0 and 1.
    • Can be used to identify substances and compare results across experiments.

Full Notes

Chromatography and background theory has been outlined in more detail here.
This page is just what you need to know for SL and AHL IB Chemistry :)

What Is Chromatography?

Chromatography is a separation technique used to identify the components of a mixture.

It relies on the distribution of substances between:

Different substances interact differently with these phases based on intermolecular forces, leading to separation.

Example: Paper Chromatography

In paper chromatography a sample dissolves in a solvent (the mobile phase) and travels up the paper (stationary phase). IB Chemistry diagram of paper chromatography showing solvent front, stationary phase, and separated components.

How Separation Occurs

A component with stronger attraction to the mobile phase (e.g. dissolves well in the solvent) will travel further during chromatography.

Whereas a component with stronger attraction to the stationary phase (e.g. sticks more to the paper) will travel a shorter distance.

This separation is caused by differences in intermolecular forces, such as:

The polarity of both the sample and the solvent plays a major role: a polar solvent will carry polar components more easily, while non-polar components tend to stay near the baseline.

Retardation Factor (Rf)

The retardation factor (Rf) quantifies how far a component travels during chromatography:

IB Chemistry diagram showing Rf value calculation from baseline to solvent front.

Rf = (distance moved by compound) ÷ (distance moved by solvent front)

Example: Polar substances in a polar solvent will usually have higher Rf values than non-polar substances in the same solvent.

Interpreting Rf Values

Summary