Two oxygen atoms can both achieve stable structures by sharing two pairs of electrons.
Atom, by itself, is rarely capable of free existence. Chemical bonds link together atoms to form molecules.The food we eat, the water we drink and the air we inhale everything is made of atoms and the molecules. so, every where around us chemical bonding exists. Out of all the types of chemical bonds covalent bond is the most common type of bond.
Covalent bond:
Covalent bond is formed by sharing of electrons between two adjacent atoms in a molecule, especially sharing a pair of electrons
between adjacent atoms. Covalent bond can be related to like two friends sharing their snacks with each other and both are
benefited. When atoms share one, two or three pairs of electrons, they are considered to have a single, double and triple bond
respectively. The maximum number of covalent bonds an atom can form is its covalency.
Covalency:
The number of electron pairs an atom can share with other atoms. Number of valence electrons of an atom decides the covalency of
that particular atom.
Polar covalent bond in HBr
Unequal sharing of bonded pair due to difference in electronegativity between hydrogen and bromine.
Bond polarity:
The difference in electronegativity of the two elements can be used to predict the nature of the chemical bond.
When difference in electronegativity are 1.7 or greater, the bond is usually ionic. Less than 1.7, the bond is usually covalent
and unless the difference is less than 0.5 the bond has some degree of polarity. Differences of less than 0.5 are considered to be
non–polar.
Polar covalent bond:
The type of a covalent bond between two atoms in which electrons are shared unequally. Unequal sharing of electrons is due to the
electronegativity difference between atoms in a molecule. The more electronegative atom pulls the shared pair of electrons towards
itself within the bond. As a result the electron pair is drawn closer towards the atom with more electronegativity which leads to
the formation of electric dipole. Partial positive charge and partial negative charges can be denoted by delta plus
(δ+) and delta minus (δ−).
An analogy is the tug of war between two teams, one team is stronger and other team is weaker team. So, the stronger team pull with
the rope with more force. Here atoms are compared with teams and rope to the electrons.
Non polar covalent bond – Hydrogen molecule
In Hydrogen molecule there is no difference in electronegativity so there is equal sharing of bonded pair.
Non–polar covalent bond:
The type of bond formed when two atoms of same element forms a covalent bond. When there is no difference in electronegativity
then the electrons are shared equally between the two atoms in a molecule.
An analogy for this is tug–of–war between two strong teams and the rope is being pulled equally and rope does not move.
So, here the two teams are atoms in a molecule and rope is the bond formed. So, the electron pair is shared equally.
Structure of Carbon dioxide showing dipole moments
Dipole moment can be defined as the product of magnitude of charge and the distance of separation between the charges. A dipole exists when electrons are unequally shared between the atoms of a molecule, leading to positive and negative ends. The larger the difference in electronegativity between bonded atoms the larger the dipole moment.
Example:
As we know that CO2 molecule is a linear molecule, the central atom is carbon surrounded by two oxygen atoms. Oxygen is
more electronegative than carbon, therefore there is a dipole between carbon atom and oxygen atoms. Since the
dipoles are in opposite directions, the net effect is that they cancel. Thus the molecule does not have a dipole. So, carbon
dioxide molecule is a non–polar molecule. Dipole moment is equal to zero.