2. Chemical formula
• A chemical formula is a notation used by scientists to show the number and
type of atoms present in a molecule, using the atomic symbols and numerical
subscripts. In a chemical formula, the letters represent the atomic symbol of
each atom. The subscript (lower) represents the number of each atom, while
the superscript (higher) represents the charge on a given atom.
3. Types of chemical formula
There are four basic types of chemical formula
1. Empirical formula
2. Molecular formula
3. Structural formula
4. Condensed formula
Empirical formula
• The empirical chemical formula represents the relative number of atoms of each
element in the compound.
• Benzene is represented by the empirical formula CH, which indicates that a typical
sample of the compound contains one atom of carbon (C) to one atom
of hydrogen (H).
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2. Molecular formula
• The molecular formula comes in to show the actual number of atoms within
each molecule.
• Example, molecular formula of benzene is C6H6
• For hydrogen peroxide the molecular formula is thus H2O2
• There are many number of compounds having the same molecular and
empirical formula. If the molecular formula cannot be simplified into a
smaller whole-number ratio, then the empirical formula is also the molecular
formula as in H2O.
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3. Structural formula
• Structural formulas identify the location of chemical bonds between the atoms
of a molecule. A structural formula consists of symbols for the atoms
connected by short lines that represent chemical bonds-one, two, or three lines
standing for single, double, or triple bonds, respectively. For example, the
structural formula of ethane is
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4. Condensed formula
• A condensed (or semi-structural) formula may represent the types and spatial
arrangement of bonds in a simple chemical substance.
• For example, ethane consists of two carbon atoms single-bonded to each
other, with each carbon atom having three hydrogen atoms bonded to it. Its
chemical formula can be rendered as CH3CH3.
• In ethylene there is a double bond between the carbon atoms (and thus each
carbon only has two hydrogens), therefore the chemical formula may be
written: CH2CH2. However, a more explicit method is to write H2C=CH2 or
less commonly H2C::CH2. A triple bond may be expressed with three lines
(HC≡CH) .
