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1.Fundamentals of Chemistry eLearn.Punjab

Table 1.9 Difference between Ions and Free Radicals

Ions Free Radicals

(i). These are the atoms which bear some charge. These are the atoms that have odd number of

electrons.

(ii). They exist in solution or in crystal lattice. They can exist in solutions as well in air.

(iii). Their formation is not affected by the presence They may form in the presence of light.
of light.

1.3.2 Types of Molecules

A molecule is formed by the chemical combination of atoms. It is the smallest unit of a substance. It
shows all the properties of the substance and can exist independently. There are different types of
molecules depending upon the number and types of atoms combining. A few types are discussed
here.

A molecule consisting of only one atom is called monoatomic molecule. For example, the inert gases
helium, neon and argon all exist independently in atomic form and they are called monoatomic
molecules.

If a molecule consists of two atoms, it is called diatomic molecule. For example: hydrogen (H2), oxygen
(O2), chlorine (Cl2) and hydrogen chloride (HCl).

If it consists of three atoms, it is called triatomic molecule. For example: H2O and CO2. If a molecule
consists of many atoms, it is called polyatomic. For example: methane (CH4), sulphuric acid (H2SO4)
and glucose (C6H12O6).

A Molecule containing same type of atoms, is called homoatomic molecule. For example: hydrogen
(H2), ozone (O3), sulphur (S8) and phosphorus (P4) are the examples of molecules formed by the
same type of atoms. When a molecule consists of different kinds of atoms, it is called heteroatomic
molecule. For example: CO2, H2O and NH3.

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