Explanation
This generally occurs between atoms of non metals. A covalent bond is formed by the mutual sharing of electrons between two atoms.
There are three types of covalent bonds based on the number of electrons shared:
single covalent bond: formed when one pair of electrons (that is two electrons) are shared between two atoms. This is represented by “-” symbol e.g H-H.
double covalent bond: formed when two pair of electrons (that is four electrons) are shared between two atoms. This is represented by “=” symbol e.g O=O.
triple covalent bond: formed when three pair of electrons (that is six electrons) are shared between two atoms. This is represented by “≡” symbol e.g N≡N.
Properties of Covalent compounds:
They can exist as crystals but are generally in liquid or gaseous state.
They usually have low melting and boiling points.
They are poor electrical conductors.
They are insoluble in polar solvents like water but dissolve well in non polar solvents like oil.
Bond polarity → Polar and Non polar covalent bonds
Non polar covalent bond: This covalent bond forms between two identical atoms as they have same electronegativity. Hence, both attract the shared pair of electrons equally. For example the single bond in between two atoms of hydrogen is non polar as both hydrogen atoms have the same electronegativity value.
Polar covalent bond: This covalent bond forms between two atoms having different electronegativity values. This causes the atom with more electronegativity to attract the shared electron pair more towards itself. This results in partial negative charge on the more electronegative atom and partial positive charge on the less electronegative atom. For example in HCl as chlorine is more electronegative so has a partial negative charge and hydrogen being less electronegative has a partial positive charge. This results in the covalent bond being polar in nature.
Electronegativity difference and nature of bonding in compounds
Electronegativity difference between two bonded atoms
More than 1.7 results in ionic bond
From 0.4 to 1.7 results in polar covalent bond
From 0.0 to 0.3 results in non polar covalent bond
Properties of polar and non polar covalent compounds
Polar covalent compounds:
Polar covalent compounds are soluble in water
They usually conduct electricity in aqueous solution
They are insoluble in non polar solvent like petrol
Examples: HF, H₂O
Non polar covalent compounds:
Non polar covalent compounds are insoluble in water.
They do not conduct electricity in solid, molten or aqueous state.
They are soluble in non polar solvents like petrol.
Examples: CH₄, C₂H₆
