How to find polar or non-polar Molecules ?

Polar and non-polar Molecule 

Polar Molecules are the Molecules whose net dipole moment is non-zero and non-polar Molecules are the Molecules whose net dipole moment is zero.

What is dipole moment ?

It is the product of charge on ions and distance between oppositely charged ions. Higher the charge on atoms or ions more will be the dipole moment . 

Covalent bond is further classified as polar Covalent bond and non-polar Covalent bond .

●Polar Covalent bond 

This type of bond is formed when there is electronegative difference between Covalently bonded atoms in a molecules . 

More electronegative atom tries to attract shared electron toward itself . This leads to partial negative charge on more electronegative atom and partial positive charge on more electropositive atom .

●Non-polar Covalent bond 

This type of bond is formed when the electronegative difference of atoms in a molecule is same or almost same . 

Bonding electrons are equally shared between Covalently bonded atoms . No partial charge formation takes place .

Points to remember 

●If the bond between two atom is polar in nature , it is not necessary that Molecule is polar Molecule . Polar nature depends on the geometry and symmetry of a molecule also . Symmetrical Molecules are always non-polar in nature (their dipole moment cancel each other and net dipole moment becomes zero )

● Molecules with linear , trigonal planar and tetrahedral geometry usually have zero dipole moment if the Molecules are symmetrical in nature.

Some examples to find polar and non-polar Molecules :

◆Carbon Dioxide (CO2)

◆Methane (CH4)

◆Ammonia (NH3)

◆Water (H20)

◆Carbon tetrachloride (CCl4)

◆Benzene (C6H6)

Carbon dioxide (CO2)

Central atom carbon is sp hybridized and has a linear structure . This structure is symmetrical due to presence of same atom in both side of carbon atom . Net dipole moment becomes zero and therefore carbon dioxide is non-polar in nature .

Methane (CH4)

Central carbon atom in Methane is sp3 hybridized and has a tetrahedral geometry.

This Molecules is symmetrical in nature .  Net dipole moment of this Molecule is zero and therefore Methane is non-polar Molecule

Ammonia(NH3)

Central Nitrogen atom in ammonia is sp3 hybridized and has pyramidal shape( 3 bond pair and 1 lone pair electrons) . Shape of ammonia is non-symmetrical in nature . Net dipole moment of this Molecule is non-zero and therefore ammonia  is polar Molecule

Water(H2O)

Central Oxygen atom in water is also sp3 hybridized and has a bent shape(V-shape).

This Molecule is non-symmetrical in nature . Net dipole moment of this Molecule is non-zero . Therefore water is a polar Molecule .

Carbon tetrachloride(CCl4)

Central carbon atom in carbon tetrachloride is sp3 hybridized and has a tetrahedral geometry. This Molecule is symmetrical in nature as like Methane . Net dipole moment of this Molecule is zero . Therefore carbon tetrachloride is a non-polar Molecule .

Benzene(C6H6)

Each carbon atom in benzene is sp2 hybridized and has a trigonal planar structure . Benzene is symmetrical in nature and all atoms are present in same plane . Net dipole moment of Benzene is zero . Therefore benzene is also a non-polar Molecule

Diatomic Molecule (same atoms)

Diatomic Molecules having same atoms like Hydrogen(H2) , Chlorine (Cl2) , Oxygen(O2) , etc  are non-polar in nature because the electronegative difference between this Molecules is zero . No charge formation takes place . 

Diatomic Molecules(Different atoms)

Diatomic Molecules with different atoms are always polar in nature . There is always some electronegative difference between different atoms .

For example ,

Hydrochloric Chlorine (HCl) is polar in nature . In this Molecule Chlorine is more electronegative than hydrogen . Chlorine carries partial negative charge whereas Hydrogen carries partial positive charge. Net dipole moment of HCl is non-zero . Therefore HCl is polar Molecule .

 Ionic Compounds can be polar or non-polar . 

For example , 

Sodium Chlorine(NaCl) is polar in nature because of large electronegative difference between Sodium and Chlorine atom. Net dipole moment is non-zero .

Aluminium Chlorine (AlCl3) is seem to be polar in nature due to large electronegative difference between Aluminium amd Chlorine atom but the overall Molecule is non polar due to symmetrical geometry of Aluminium Chloride . Net dipole moment of this Molecule is zero.