Review on Elements learnt in IX Class
In Class IX you have learnt about various elements. You have seen that elements can be classified as metals or non-metals on the basis of their properties. Once we shall recap of what you have learnt in Class IX
On the basis of their chemical composition, substances can be classified either as elements or compounds.
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:
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:
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.
More to know
The number of elements known at present is more than 100. Ninety-two elements are naturally occurring and the rest are man-made.
Majority of the elements are solid.
Eleven elements are in a gaseous state at room temperature.
Two elements are liquid at room temperature–mercury and bromine.
Elements, gallium and caesium become liquid at a temperature slightly above room temperature (303 K).
Think of some uses of metals and non-metals in your daily life.
What properties did you think of while categorising elements as metals or non-metals?
How are these properties related to the uses of these elements? Let us look at some of these properties in detail.