Dipole moment :
The polarity of a covalent bond can be measured in terms of dipole moment which is defined as \(\mu=q \times 2d\)
Where \(\mu\) is the dipole moment, q is the charge and 2d is the distance between the two charges.
Where p is the dipole moment, q is the charge and 2d is the distance between the two charges. The dipole moment is a vector and the direction of the dipole moment vector points from the negative charge to positive charge.

The unit for dipole moment is columb meter (C m). It is usually expressed in Debye unit (D). The conversion factor is 1 Debye = 3.336 x 10^-30 C m.

Linear combination of atomic orbitals:
1. The wave functions for the molecular orbitals can be obtained by solving Schrodinger wave equation for the molecule. Since solving the Schrodinger equation is too complex, approximation methods are used to obtain the wave function for molecular orbitals. The most common method is the linear combination of atomic orbitals (LCAO).
2. The atomic orbitals are represented by the wave function \(\Psi \). Let us consider two atomic orbitals represented by the wave function \(\Psi _A\) and \(\Psi _B\) with comparable energy, combines to form two molecular orbitals. One is bonding molecular orbital (\(\Psi \)_bonding) and the other is antibonding molecular orbital (\(\Psi \)_antibondin ). The wave functions for these" two" molecular orgitals can be obtained by the linear combination of the atomic orbitals \(\Psi _A\) and \(\Psi _B\) as beIow.
\(\Psi _{bonding}=\Psi _A+\Psi _B\\ \Psi _{antibonding}=\Psi _A-\Psi _B\)
3.The formation of bonding molecular orbital can be considered as the result of constructive interference of the atomic orbitals and the formation of antibonding molecular orbital can be the result of the destructive interference of the atomic orbitals. The formation of the two molecular orbitals from two 1s orbitals is shown below.
4.Constructive interaction : The two 1s orbitals are in phase and have the same sign.

Molecular orbital diagram of oxyge molecule (O₂) :
Electronic configuration of O atom 1s²2s²2p⁴
Electronic configuration of O₂ molecule
\(\sigma^{2}_{1s},\sigma^{*2}_{1s},\sigma^{2}_{2s},\sigma^{*2}_{2s},\sigma^{2}_{2px},\)\(\pi^{2}_{2py},\pi^{2}_{2pz},\pi^{*1}_{2py},\pi^{*1}_{2pz}\)
Bond order=\({N_b-N_a\over2}={10-6\over2}=2\)
Molecule has two unpaired electrons hence it is paramagnetic.

In CH₄, NH₃ and H₂O the central atoms are sp³ hybridised. So, the expected structure for all these compounds are tetra hedron and the bond angles 109^o 28'. But due to the presence of one ione pair of electrons on Nitrogen atom on ammonia and the two lone pairs of electrons on oxygen atom of water the structure deviates and the bond angles vary. The lone pairs of electrons occupy more space and they repel the electrons in the covalent bonds.