TABLE OF CONTENTS This chapter provides a brief insight into selected fundamental principles of matter as a background to the appreciation of the hazards of chemicals.
Chemistry is the science of chemicals which studies the laws governing their formation, combination and behaviour under various conditions. Some of the key physical laws as they influence chemical safety are discussed in Chapter 4.
Chemicals are composed of atoms, discrete particles of matter incapable of further subdivision in the course of a chemical reaction. They are the smallest units of an element. Atoms of the same element are identical and equal in weight. All specimens of gold have the same melting point, the same density, and the same resistance to attack by mineral acids. Similarly, all samples of iron of the same history will have the same magnetism. Atoms of different elements have different properties and differ in weight.
Atoms are comprised of negatively charged electrons orbiting a nucleus containing positively-charged protons and electrically-neutral neutrons as described in Chapter 11. The orbits of electrons are arranged in energy shells. The first shell nearest to the nucleus can accommodate two electrons, the second shell up to eight electrons, the third 18 electrons, and the fourth 32 electrons. This scheme is the 'electronic configuration' and largely dictates the properties of chemicals. Examples are given in Table 3.1.
| Element | Symbol | Atomic (proton) number | No. electrons in 1 st shell | No. electrons in 2nd shell | No. electrons in 3rd... |
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