TABLE OF CONTENTS Elements. There are a very large number of different substances in existence, each substance containing one or more of a number of basic materials called elements. An "element" is a substance which cannot be separated into anything simpler by chemical means. There are 92 naturally ocurring elements and 13 others, which have been artificially produced.
Some examples of common elements with their symbols are: Hydrogen (H), Helium (He), Carbon (C), Nitrogen (N), Oxygen (O), Sodium (Na), Magnesium (Mg), Aluminium (A1), Silicon (Si), Phosphorus (P), Sulphur (S), Potassium (K), Calcium (Ca), Iron (Fe), Nickel (Ni), Copper (Cu), Zinc (Zn), Silver (Ag), Tin (Sn), Gold (Au), Mercury (Hg), Lead (Pb) and Uranium (U).
Elements are made up of very small parts called atoms. An "atom" is the smallest part of an element that can take part in a chemical change and retain the properties of the element. Each of the elements has a unique type of atom.
Atoms. In atomic theory, a model of an atom can be regarded as a miniature solar system. Atoms contain a dense nucleus of positively charged protons and uncharged neutrons, surrounded by negatively charged orbital electrons that occupy discrete energy levels and orbital configurations (see Fig. 4.1). In a stable atom, the positively charged protons and the negatively charged electrons are equal. Each type of atom, or element, is assigned a mass number based on the number of protons and neutrons contained in its nucleus. Mathematically these...
