Chemistry

Topic

6

Microscopic World II

Unit 23 Shapes of molecules Unit 24 Bond polarity and intermolecular forces

Key

C o ncepts

Microscopic World II

Shapes of molecules • Covalent molecules with non-octet structures • Shapes of molecules • The VSEPR theory • Molecular crystals of buckminsterfullerene (C60) • Carbon nanotubes

Bond polarity and intermolecular forces • Electronegativity and bond polarity • Van der Waals’ forces • Factors affecting the strength of van der Waals’ forces • Hydrogen bonding • Surface tension and viscosity of liquids



Topic 6

Microscopic World II

Unit 23 Shapes of molecules



Unit 23
23.1 23.2 23.3 23.4 23.5 23.6 23.7

Shapes of molecules
Covalent molecules with non-octet structures Shapes of molecules of methane, ammonia and water Shapes of some other molecules Influence of the nature of electron pairs on bond angles in molecules of methane, ammonia and water Shapes of some polyatomic ions Shapes of molecules with multiple bonds Molecular crystals of buckminsterfullerene (C60)

23.1 – 23.7 Summary
1 Examples of covalent molecules with non-octet structures are as follows:
Molecule Electron diagram F BF3 B F F SF4 F Molecule Electron diagram F S F F

Cl PCl5 Cl

Cl P Cl Cl SF6

F F

F S F

F F

2 The following table summarizes the relationship between the arrangement of electron pairs around the central atom of a molecule or polyatomic ion and the shape of the species.
Total number of electron pairs* in the outermost shell of the central atom of a molecule or polyatomic ion 2 linear

Arrangement of electron pairs*

Shape of the molecule or polyatomic ion

Example(s)

B

A linear B

B

BeCl2 CO2 CS2

3 trigonal planar

A B B trigonal planar B B A B B

BF3

CH4 SiF4 NH4
+

tetrahedral

PCl4+

NH3 4 tetrahedral B A B B PH3 NCl3 H3O+

trigonal