Atomic structure

Matter is composed of tiny particles called atoms. The atom is a complex unit of various particles, the most important of which are electrons, protons, and neutrons. The difference between atoms of different elements is due to differences in the number of protons and neutrons in the nucleus and to differences in the arrangement of the electrons surrounding the nucleus. The mass of the atom is concentrated almost entirely in the nucleus.

The chemical properties of different elements can be explained by the structure of the atom. Chemical changes involve a shifting of outer (valence) electrons so that a shell is achieved. The activity of metals and non-metals is related to the size of the atom and to the number of electrons in the external orbit. The valence or combining capacity of an atom is determined by the number of electrons it gains, loses or shares in chemical combinations with atoms of other elements. Atoms also may be joined to other atoms by sharing pairs of electrons. This process produces covalent compounds. These are generally gases or liquids with low boiling points. Oxidation involves the loss of electrons by the element. The process is accompanied by an algebraic increase in valence. Reduction, on the other hand, involves a gain of electrons by the substance reduced. This process is accompanied by an algebraic decrease in valence.