Name: Hybridisation in SF₆ Molecule
Uploaded: 2019-07-19
Duration: 2 min 31 s
Description: Understand the bonding present in the case of sulphur hexafluoride. This video illustrates that the hybridisation present in the case of sulphur hexafluoride...

Question

Why are some covalent bonds polar? What is a dipole? How can a molecule that has polar bonds be a non-polar molecule? How do dipole moments of molecules of

{CO}_{2}, {CH}_{4}, H_{2} O

and

{NH}_{3}

help in ascertaining their structure?

Accepted Answer

Some covalent bonds are polar: It is due to electronegativity difference between bonded atoms. The atoms which has higher value of electro negativity will gain partially negative charge and the atom which has lower value of electro negativity will gain partially positive charge.
As for example in $HCl$ , the electro negativities of $Cl and H are 3.0 and 2.1$ respectively, $H$ gains partially positive charge due to lower electro negativity and $Cl$ gains partially negative due to higher electro negativity. There for $HCl$ is polar.

In a polar bond, one of the contributing elements becomes more positively charged than other due to its high electro positivity. Now the element attracts the bonded electron pair towards it using coulomb force and the lone pair comes in between the elements. Now as the electron cloud finds it place just in between the elements, hence no net charge is formed in any side of molecule, thus making it non-polar.

Dipole is a pair of equal and oppositely charged or magnetized poles separated by a distance.

Dipole moment of molecule of ${CO}_{2}, {CH}_{4}, H_{2} O and {NH}_{3}$ help in ascertaining their structure:
For ${CO}_{2}$ :
Carbon di-oxide is a linear molecule in which two $C = O$ bonds are oriented in the opposite directions at an angle of $180 °$ .
The dipole moment of each $C = O$ bond is $2.3 D$ , but due to linear geometry of ${CO}_{2}$ the dipole moment of one $C = O$ bond cancels that of another.
∴ Resulting dipole moment of molecule is zero, Hence ${CO}_{2}$ is non-polar molecule

For ${CH}_{4}$ :
Methane has a symmetrical tetrahedral shape and has dipole moment zero.

For ${NH}_{3}$ :
${NH}_{3}$ has a pyramidal shape with on lone pair on nitrogen atom, and it has $3$ bond pairs.
in case of nitrogen, $N$ is more electro negative than $H$ , (electro negativity of $H = 2.1 N = 3.0)$ therefore, the dipole of $N - H$ bond is from $H$ to $N$ . The orbital dipole due to lone pair is in the same direction as the resultant dipole moment of $3 N - H$ bonds. Therefore it adds on the resultant dipole moment of the $N - H$ bonds.

For $H_{2} O$ :

As a polyatomic molecule has more than one polar bond, the dipole moment is equal to the resultant dipole moment of all the individual bonds (called bond moments). The magnitude of this resultant dipole moment not only depends upon the values of the individual dipole moments of the bonds but also on their arrangement in space. For example, dipole moment of water is $1 \cdot 84 D$ which is equal to the resultant dipole moment of two $O - H$ bonds.

Why are some covalent bonds polar? What is a dipole? How can a molecule that has polar bonds be a non-polar molecule? How do dipole moments of molecules of ${CO}_{2}, {CH}_{4}, H_{2} O$ and ${NH}_{3}$ help in ascertaining their structure?

Important Questions on Chemical Bonding and Molecular Structure

Learn and Prepare for any exam you want !

Why are some covalent bonds polar? What is a dipole? How can a molecule that has polar bonds be a non-polar molecule? How do dipole moments of molecules of CO2 , CH4 , H2O and NH3 help in ascertaining their structure?

Important Questions on Chemical Bonding and Molecular Structure

Learn and Prepare for any exam you want !

Why are some covalent bonds polar? What is a dipole? How can a molecule that has polar bonds be a non-polar molecule? How do dipole moments of molecules of ${CO}_{2}, {CH}_{4}, H_{2} O$ and ${NH}_{3}$ help in ascertaining their structure?