Introduction
"The underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are thus completely known, and the difficulty is only that the application of these laws leads to equations much too complicated to be soluble."
(P.A.M. Dirac, Proceedings of the Royal Society A123, 714, 1929)
The aim of chemistry is to understand matter- how its properties arise, and how it is transformed from one form to another. At temperatures and pressures readily accessible to us on the surface of the Earth, these properties and transformations arise from 'what the electrons are doing'. What are these things called electrons? We will consider first what we know about the electron as an independent entity, then discuss its behaviour in bound systems of increasing complexity- atoms, then molecules.
Before we get stuck into things seriously, this first chapter surveys a number of key ideas which together form a framework for understanding chemical structure and reactivity. Most of them should be familiar to you from first year.
Coulomb's Law
The interactions between electrons and nuclei in atoms and molecules are really no different than the interactions between negatively and positively charged objects on a macroscopic scale- for example, balloons.
- Like charges repel; unlike charges attract.
- The strength of the repulsion or attraction is directly proportional to the charge on each object.
- The strength of the repulsion or attraction falls away with the square of the distance between the objects.
Microscopically and macroscopically, then, the strength of the force between two charged objects of charge q1 and q2 separated by a distance r is:
| F = | q1q2 |
| r2 |
