DEFINITIONS
 
 
MOLECULAR FORMULA
 
The molecular formula of a compound is defined as:
"The formula of a compound which not only expresses the relative number of atoms of each kind but also expresses the actual number of atoms of each element present in one molecule".
Molecular formula and empirical formula of a compound are related as:
MOLECULAR FORMULA = (EMPIRICAL FORMULA)n
   Where "n" is an integer and is given by:
   n = molecular mass of compound / Empirical formula mass of compound
   Molecular formula of propane = C3H8.
   Molecular formula of sugar = C12H22O11.
SYMBOL
 
   A symbol is an abbreviation or short form for the chemical name of an element
   A symbol represents only one atom of an element.
   EXAMPLE:
   Carbon = C, Hydrogen= H, Chlorine = Cl, Gold = Au, Silver = Ag, Sodium = Na, bismuth = Bi etc.
FORMULA
 
The representation of a molecule of a substance or compound in
the form of symbols is called "formula".
   With the help of formula we can find.
   (1) Name of elements present in the molecule.
   (2) Number of atoms of each element.
   (3) Composition of compound.
   EXAMPLE:
   NH3, CO2, CaCO3, H2O, H2SO4 etc.
COMPOUND
 
"Compounds are pure substances, which consist of two or
more elements combined chemically in a fixed ratio."
   Compounds always have a definite composition.
   EXAMPLE:
   H2SO4, CaCl2, H2O, CO2 etc.
MIXTURE
 
"A mixture is a substance, which consists of two or more pure substances
not chemically combined with each other in a definite composition ."
   Mixtures do not have definite composition.
   EXAMPLE:
   Air, soil, brass ( cu + zinc) etc.
DIFFERENCE BETWEEN COMPOUND AND MIXTURE
S.No
COMPOUND
MIXTURE
1.
It is a pure substance. It is an impure substance.
2.
It can not be separated by physical method. It can be separate by physical method.
3.
Element loose their properties in a compound. Substances forming mixture retain their properties.
4.
Its composition is fixed through out its mass. It has no fixed composition.
5.
It has fixed melting point. It has no sharp melting point.
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