The octet rule and Lewis structures, formal charge and its limits, the ionic bond and lattice enthalpy, and the bond length, angle, enthalpy and order that describe any bond.
3 lessons, about 1 h 20 min3 simulations11 problems4 practice questionsPython in every lesson
Kossel and Lewis explained bonding by the octet rule: atoms lose, gain or share electrons to reach eight in the outer shell. A Lewis structure counts every valence electron and shows shared pairs and lone pairs. Formal charge picks the best structure. Some molecules break the rule: incomplete octets, odd electrons and expanded octets.
An ionic bond forms when a metal with a low ionisation enthalpy gives electrons to a non-metal with a negative electron gain enthalpy. Making the gaseous ions alone costs energy. The lattice enthalpy, released when the ions pack into a crystal, pays for it. A Born-Haber cycle adds up the steps to give the enthalpy of formation.
Four parameters describe a covalent bond: its length, the angle it makes with other bonds, its enthalpy and its order. More shared pairs make a bond shorter and stronger. When one Lewis structure is not enough, the real molecule is a resonance hybrid. Unequal sharing makes a bond polar, and its dipole moment is charge times distance.
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