Physical Chemistry #9: Sigma and Pi Bonds, Hybridisation and Molecular Geometries (Slides & Tasks)

In this lesson we discuss the formation of sigma and pi bonds, the hybridisation of orbitals and the molecular geometries that form due to electron repulsion. This is lesson nine in our physical chemistry series for Unit 3: Chemical Bonding (from the Cambridge International AS Chemistry Curriculum (9701) 2019-2021 curriculum).

LESSON OBJECTIVE: Understand how sigma and pi bonds form and investigate the concept of atomic orbital hybridisation. Identify molecular geometries and understand bond angles observed due to electron pair repulsion.

Learning Outcomes: (from the Cambridge AS Chemistry Curriculum 2019-2021):
3.2 Covalent bonding and co-ordinate (dative covalent) bonding including
shapes of simple molecules
b) describe covalent bonding in terms of orbital overlap, giving σ and π bonds, including the concept of hybridisation to form sp, sp2 and sp3 orbitals (see also Section 14.3)

c) explain the shapes of, and bond angles in, molecules by using the qualitative model of electron-pair repulsion (including lone pairs), using as simple examples BF3 (trigonal planar), CO2 (linear), CH4 (tetrahedral), NH3 (pyramidal), H2O (non-linear), SF6 (octahedral), PF5 (trigonal bipyramidal)

d) predict the shapes of, and bond angles in, molecules and ions analogous to those specified in 3.2© (see also Section 14.3)