Robert Boyle was the first scientist to use the term element in 1661. Antoine Laurent Lavoisier (1743-94), a French chemist, was the first to establish an experimentally useful definition of an element. He defined an element as a basic form of matter that cannot be broken down into simpler substances by chemical reactions.
Elements can be normally divided into metals, non-metals and metalloids.
Metals usually show some or all of the following properties:
• They have a lustre (shine).
• They have silvery-grey or golden-yellow colour.
• They conduct heat and electricity.
• They are ductile (can be drawn into wires).
• They are malleable (can be hammered into thin sheets).
• They are sonorous (make a ringing sound when hit).
Examples of metals are gold, silver, copper, iron, sodium, potassium etc. Mercury is the only metal that is liquid at room temperature.
Non-metals usually show some or all of the following properties:
• They display a variety of colours.
• They are poor conductors of heat and electricity.
• They are not lustrous, sonorous or malleable.
Examples of non-metals are hydrogen, oxygen, iodine, carbon (coal, coke), bromine, chlorine etc.
Some elements have intermediate properties between those of metals and non-metals, they are called metalloids; examples are boron, silicon, germanium etc.
• The number of elements known at present are more than 100. Ninety-two elements are naturally occurring and the rest are manmade.
• Majority of the elements are solid.
• Eleven elements are in gaseous state at room temperature.
• Two elements are liquid at room temperature–mercury and bromine.
• Elements, gallium and cesium become liquid at a temperature slightly above room temperature (303 K).