“Chemical Bonding: Olympiad Practice” is available to Standard subscribers.
The hard questions of the chapter: dipole moments and molecular shape, tricky Lewis structures and formal charges, back bonding and bridges, and comparing bond lengths and energies, with a full paper.
3Lessons11Problems2Python Labs1Question Set1Mock Test
Dipole moments and shape: A dipole moment has a size and a direction, so the dipole of a molecule is the vector sum of its bond dipoles and lone pairs. Symmetric shapes cancel to zero. A measured dipole tells the shape of a molecule, how ionic a bond is, and a cis isomer from a trans one.
Tricky structures and formal charges: Formal charges pick the best of several Lewis structures: the smallest charges, with any negative charge on the most electronegative atom. Atoms from period 3 down can hold more than eight electrons, and molecules with an odd number of electrons keep one unpaired. Boron makes up for its empty orbital by back bonding, and diborane by bridges.
Comparing bonds: Bonds get shorter and stronger as the bond order rises, and longer as the atoms get bigger. Resonance gives ions bond orders between whole numbers. Bond angles shrink down a group and when the outer atoms pull harder. Fajans' rules tell when an ionic bond turns partly covalent.