Bonding, structure and intermolecular forces: every key term you need (+ practice quiz)

Ionic bonding

Electrostatic attraction between oppositely charged ions in a giant lattice. Gives high melting points and conductivity only when molten or aqueous.

Dative covalent bond

A covalent bond where both electrons come from the same atom. Shown by an arrow, as in the ammonium ion.

Metallic bonding

Attraction between a lattice of positive ions and delocalised electrons. Explains conductivity, malleability and high melting points.

Electronegativity

An atom's ability to attract the electron pair in a covalent bond. Increases across a period and decreases down a group.

Permanent dipole

Arises when bonded atoms differ in electronegativity, producing partial charges and a polar molecule if the dipoles do not cancel.

Van der Waals forces

Induced dipole-dipole attractions from instantaneous fluctuations in electron density. Strength rises with molecular size and surface contact.

Hydrogen bonding

Strong dipole attraction where hydrogen is bonded to nitrogen, oxygen or fluorine. Explains water's anomalously high boiling point.

Ice density anomaly

Hydrogen bonds hold water molecules in an open lattice on freezing, so ice is less dense than liquid water and floats.

Electron pair repulsion theory

Electron pairs around a central atom repel to the maximum separation. Lone pairs repel more strongly, closing bond angles by about 2.5 degrees each.

Tetrahedral shape

Four bonding pairs and no lone pairs, giving bond angles of 109.5 degrees — as in methane.

Octahedral shape

Six bonding pairs at 90 degrees to each other, typical of many transition metal complexes.

Giant covalent structure

A lattice of atoms joined by strong covalent bonds throughout, as in diamond and silicon dioxide. Very high melting points, generally insoluble.

Graphite conductivity

Each carbon bonds to three others, leaving one delocalised electron per atom free to move along the layers.

Simple molecular lattice

Discrete molecules held by weak intermolecular forces. Low melting points, because only those forces break on melting — not covalent bonds.

Bond polarity vs molecular polarity

A molecule with polar bonds can still be non-polar overall if the dipoles are symmetrical and cancel, as in carbon dioxide.

Solubility and polarity

Polar solutes dissolve in polar solvents and non-polar in non-polar, because only then can solute-solvent interactions replace those broken.

More A-Level Chemistry guides

• Atomic structure and the periodic table
• Amount of substance and quantitative chemistry
• Energetics and thermodynamics
• Kinetics, equilibria and acids
• Redox, electrochemistry and transition metals