14.1.1

Predict the shape and bond angles for species with five and six negative charge centres using the VSEPR theory.

3

Examples should include PCl5, SF6, XeF4 and PF6–.

Aim 7: Interactive simulations are available to illustrate this.

14.2.1

Describe σ and π bonds.

2

Treatment should include:

• σ bonds resulting from the axial overlap of orbitals

• π bonds resulting from the sideways overlap of parallel p orbitals

• double bonds formed by one σ and one π bond

• triple bonds formed by one σ and two π bonds.

14.2.2

Explain hybridization in terms of the mixing of atomic orbitals to form new orbitals for bonding.

3

Students should consider sp, sp2 and sp3 hybridization, and the shapes and orientation of these orbitals.

TOK: Is hybridization a real process or a mathematical device?

14.2.3

Identify and explain the relationships between Lewis structures, molecular shapes and types of hybridization (sp, sp2 and sp3).

3

Students should consider examples from inorganic as well as organic chemistry.

14.3.1

Describe the delocalization of π electrons and explain how this can account for the structures of some species.

3

Examples should include NO3–, NO2–, , O3, RCOO– and benzene.

TOK: Kekulé claimed that the inspiration for the cyclic structure of benzene came from a dream. What role do the less rational ways of knowing play in the acquisition of scientific knowledge? What distinguishes a scientific from a non-scientific hypothesis: its origins or how it is tested?