Structure 2.1—The ionic model

Structure 2.1.1—When metal atoms lose electrons, they form positive ions called cations. When non-metal atoms gain electrons, they form negative ions called anions.

Structure 2.1.2—The ionic bond is formed by electrostatic attractions between oppositely charged ions

Structure 2.1.3—Ionic compounds exist as three-dimensional lattice structures, represented by empirical formulas.

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Structure 2.2—The covalent model

Structure 2.2.1—A covalent bond is formed by the electrostatic attraction between a shared pair of electrons and the positively charged nuclei. The octet rule refers to the tendency of atoms to gain a valence shell with a total of 8 electrons.

Structure 2.2.2—Single, double and triple bonds involve one, two and three shared pairs of electrons respectively.

Structure 2.2.3—A coordination bond is a covalent bond in which both the electrons of the shared pair originate from the same atom.

Structure 2.2.4—The valence shell electron pair repulsion (VSEPR) model enables the shapes of molecules to be predicted from the repulsion of electron domains around a central atom.

Structure 2.2.5—Bond polarity results from the difference in electronegativities of the bonded atoms.

Structure 2.2.6—Molecular polarity depends on both bond polarity and molecular geometry.

Structure 2.2.7—Carbon and silicon form covalent network structures.

Structure 2.2.8—The nature of the force that exists between molecules is determined by the size and polarity of the molecules. Intermolecular forces include London (dispersion), dipole-induced dipole, dipole–dipole and hydrogen bonding.

Structure 2.2.9—Given comparable molar mass, the relative strengths of intermolecular forces are generally: London (dispersion) forces < dipole–dipole forces < hydrogen bonding.

Structure 2.2.10—Chromatography is a technique used to separate the components of a mixture based on their relative attractions involving intermolecular forces to mobile and stationary phases.

AHL ONLY

Structure 2.2.11—Resonance structures occur when there is more than one possible position for a double bond in a molecule.

Structure 2.2.12—Benzene, C₆H₆, is an important example of a molecule that has resonance.

Structure 2.2.13—Some atoms can form molecules in which they have an expanded octet of electrons.

Structure 2.2.14—Formal charge values can be calculated for each atom in a species and used to determine which of several possible Lewis formulas is preferred.

Structure 2.2.14—Formal charge values can be calculated for each atom in a species and used to determine which of several possible Lewis formulas is preferred.

Structure 2.2.16—Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals for bonding

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Structure 2.3—The metallic model

Structure 2.3.1—A metallic bond is the electrostatic attraction between a lattice of cations and delocalized electrons.

Structure 2.3.2—The strength of a metallic bond depends on the charge of the ions and the radius of the metal ion.

Structure 2.3.3—Transition elements have delocalized d-electrons.

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Structure 2.4—From models to materials

Structure 2.4.1—Bonding is best described as a continuum between the ionic, covalent and metallic models, and can be represented by a bonding triangle.

Structure 2.4.2—The position of a compound in the bonding triangle is determined by the relative contributions of the three bonding types to the overall bond.

Structure 2.4.3—Alloys are mixtures of a metal and other metals or non-metals. They have enhanced properties.

Structure 2.4.4—Polymers are large molecules, or macromolecules, made from repeating subunits called monomers.

Structure 2.4.5—Addition polymers form by the breaking of a double bond in each monomer.

Structure 2.4.6—Condensation polymers form by the reaction between functional groups in each monomer with the release of a small molecule.

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