ChemistryCode 9701
Intermolecular forces, electronegativity and bond properties
What this topic asks you to be able to do
- describe hydrogen bonding, limited to molecules with N–H and O–H groups, including the simple cases of ammonia and water (b) use the idea of hydrogen bonding to explain why H₂O (ice and water) behaves unusually: • its melting and boiling points are relatively high • its surface tension is also relatively high • how the density of solid ice compares with that of liquid water
- use ideas about electronegativity to explain how polar a bond is and what dipole moment a molecule has
- describe van der Waals’ forces as any intermolecular forces acting between molecular entities apart from those that arise from forming bonds, and use van der Waals’ forces as an umbrella name covering every kind of intermolecular force (b) describe the kinds of van der Waals’ forces: • id-id forces (instantaneous dipole–induced dipole), also known as London dispersion forces • pd-pd forces (permanent dipole–permanent dipole), including hydrogen bonding (c) describe hydrogen bonding, and understand it as a particular type of pd-pd force that acts between molecules in which hydrogen is joined to a highly electronegative atom
- state that, generally speaking, the bonding in ionic, covalent and metallic substances is stronger than intermolecular forces