There are many substances in this world, such as iron, air and soil. They are all different from one another in composition, properties and uses. They are made up of different kinds of matter, and can be pure or impure. These substances are divided into three main categories on the basis of their similarities and dissimilarities; elements, compounds and mixtures.
Pure and Impure substances:
Pure substances: Pure substances have a definite composition and properties such as the boiling point, melting point and density, etc. Their composition is uniform throughout the bulk. Both elements and compounds are pure substances. Impure substances: Impure substances are made up of two or more pure substances mixed together in any proportion. They do not have any definite set of properties and retain the properties of the substances that make them. They may have uniform composition throughout or non uniform composition throughout. They are all mixtures.
Elements:
An element is a pure substance that cannot be converted further into anything simpler than itself by any physical or chemical process. So, each elements has its own unique set of properties. Some examples are oxygen, silver, carbon, sulphur, etc. These elements are made of extremely small particles called atoms which cannot be seen through human eyes. Now, 118 elements are known, out of which 92 are natural and 26 have been artificially made. Most elements are found in their combined state in the earth's crust. Some elements are solids, others can be either liquids or gases. In fact, elements are the basic pure substances from
which millions of substances are made. Classification of Elements:
Based on their properties, elements have been classified into metals, non-metals, metalloids and noble or inert gases. Metals: Most elements known to us are metals, such as gold, silver and aluminum. Non-metals: Excluding inert gases, there are only eleven non-metals known to us. Their examples are hydrogen, oxygen, carbon, nitrogen, etc. Metalloids: These elements show some properties of metals and some of non-metals. They are hard solids. Examples are boron, silicon, antimony, etc. Noble or Inert gases: These elements do not react chemically with other elements of compounds. They are only six inert gases which we know, they are, helium, neon, argon, krypton, xenon and radon.
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