"An element is a pure substance which is made up of only one kind of atoms having the same atomic number."
"The smallest particle of an element is the atom which, has all the properties of that element."
"An element cannot be broken down into simpler substances by any physical or chemical process."
Remember:-
However, in nuclear reactions, elements having high atomic mass can be split into lighter elements.
Elements can be divided into two groups, namely, naturally occurring and artificially prepared. There are ninety naturally occurring elements. Three hundred years ago the scientists all over the world knew only twelve elements but today they know many more. About 14 elements have been artificially prepared in the laboratories. These artificially prepared elements, however, have a very short life, as they break up into more stable lighter elements.
Elements can be broadly divided into 4 categories: Metals, Non-metals, Metalloids and Noble Gases.
Metalloids are the elements, which have properties that lie between those of metals and non-metals, e.g., arsenic, antimony, etc.
Molecules of elements may consist of single atom, two atoms, or even more.
All the hundreds of thousands of compounds existing, and produced by man, are formed as a result of combination of two or more of these elements in fixed proportion.
Remember:-
Noble gases, some metals, carbon, silicon etc. have only one atom in their molecules. These are called monatomic molecules. Some elements have two atoms in their molecules. These are called diatomic molecules e.g. hydrogen (H2), oxygen (O2), nitrogen (N2), chlorine (Cl2), etc. Those elements that have more than two atoms in their molecules are said to be polyatomic. For e.g., a molecule of phosphorus consists of four atoms (P4), and that of sulphur contains eight atoms (S8).
Most of the elements are solids, while eleven of them are gases and only two are liquids. Of the two liquids, mercury, is a metal and bromine is a non-metal. However, two other metals can also exist in the liquid state at around 30oC. These two metals are gallium and caesium (gallium melting point = 29.9oC and caesium melting point = 28.6oC).
