Covalent compounds also called molecules have properties distinct from those of ionic compounds including differences in melting and boiling points, hardness, solubility, and electrical conductivity. Covalent bond is classified into three types as follows,
- Single covalent bond – share one pair (2) of electrons in valance shell
- Double covalent bond – share two pair (4) of electrons in valance shell
- Triple covalent bon – share three pair (6) of electrons in valance shell
Covalent compounds are generally softer and more flexible than ionic compounds. By being able to slide and move past each because they have less attractive forces than ionic compounds, the covalent molecules are not found in the rigid conformations characteristic of ionic compounds.
Covalent bonds between atoms inside a molecule are very strong and a large amount of energy has to be put in to break them such as burning or strong heat. However the attraction between one covalent molecule and its neighbour is usually quite weak.
Formation of hydrogen chloride molecule
The hydrogen chloride is composed of molecules in which the atoms are held by a bonding that is largely covalent. When hydrogen chloride is dissolved in water an acid is formed which is almost completely ionized. This indicates that there is an interaction between the hydrogen molecules and the water molecules to produce hydrated chloride and hydronium ions. This type of bond is called single covalent bond.
Diagrammatic representation of formation of hydrogen chloride molecule. Formation of oxygen molecule
As atom of oxygen has 6 electrons in its outermost shell it requires 2 more electrons to complete the octet and attain configuration f neon. The oxygen atom gets these electrons by mutually sharing its two electrons with the two electrons of another oxygen atom. So two oxygen atoms share two electrons each and form a double covalent bond. This type of bond is called double covalent bond.
Diagrammatic representation of formation of oxygen molecule. Formation of nitrogen molecule
The atomic number of nitrogen is 7 and its electronic configuration is , 5. This means nitrogen has 5 electrons in its outermost shell. So nitrogen needs three more electrons to complete the octet and attain configuration of the nearest noble gas and become stable. Thus two nitrogen atoms combine together by sharing three pairs of electrons to form a triple bond between two nitrogen atoms.
Since nitrogen atoms share three pairs of electrons among themselves the bond between them is called a triple covalent bond or just a triple bond.