Points to Remember
* A symbol is an abbreviation of the name of an element.
• A symbol represents an element and an atom of the element.
* The formula of an element or a compound represents a molecule of the element or compound. It gives the
number(s) of atoms of the same or different elements present in the molecule.
* Noble gases (helium, neon, argon, krypton and xenon) are monoatomic, whereas hydroken, en
oxygen, fluorine, chlorine, bromine and lodine are diatomie. Ozone (O, ) is a triatomic gas.
A 2.. The capacity of an element to combine with other elements is known as its valency.
• The formula of a compound containing two elements is obtained by transposing their valencies.
• Some elements like Iron (Fe), copper (Cu), lead (Pb). phosphorus (P) and sulphur(S) have variable valency,
• A group of atoms of two or more elements, which behaves like a single atom and has a valeney, is known
as a compound radical.
• Chemical changes are represented by chemical equations.
• The number of atoms of each element on the reactant side must be the same as that on the product side
An equation that satisfies this rule is called a balanced chemical equation
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