Question

Dipole moment of ${H_2}S$ is $0.95D$ . Calculate the bond moment if the bond angle is $97^\circ$ . $(\cos 48.5^\circ = 0.662)$

Answer 1

The bond dipole $\mu$ is given by, $\mu = \delta d$ . So, the dipole moment is the product of the magnitude of the charge and the distance between the two atoms in the covalent bonds.

Complete answer:

Dipole moment occurs between two ions in an ionic bond or between atoms in a covalent bond only when there is a separation of charge. Dipole moments arise from differences in electronegativity and the larger the difference in electronegativity, the larger is the dipole moment. But the bond moment is the degree of polarity of a chemical bond that is calculated from the value of the force of the response of the bond when the bond is subjected to an electric field.

So, the bond dipole $\mu$ is given by, $\mu = \delta d$ . (where, $\mu$ is the dipole moment, $\delta$ is the value of charge, and $d$ is the distance between two atoms in the covalent bond)

Putting all the values in the equation, we get,

$\mu = 2$ (H-S bond moment) $\times \cos (\dfrac{\phi }{2})$

$\mu = 2$ (H-S bond moment) $\times \cos (\dfrac{{97^\circ }}{2})$

$0.95 = 2$ (H-S bond moment) $\times \cos 48.5^\circ$

$0.95 = 2$ (H-S bond moment) $\times 0.662$

H-S bond moment $= \dfrac{{0.95}}{{0.662 \times 2}}$

H-S bond moment $= \dfrac{{0.95}}{{1.324}} = 0.717 \approx 0.72$

So, the bond moment is $0.72$ .

Additional Information:

Both the terms “bond moment” and “dipole moment” are based on the same principle, but their corresponding applications are different from each other. The bond moment is the polarity of a chemical bond, which is located within a certain molecule, whereas, dipole moment occurs only when there is any kind of separation between the charges. Also, a bond moment occurs in a chemical covalent bond, whereas, occurs between two ions in an ionic bond or between atoms in a covalent bond.

Note:

The dipole moment is the product of the magnitude of the charge and the distance between the two atoms in the covalent bonds. Always remember, at the time of the creation of a bond dipole moment, the electrical charges are separated as partial charges $\delta +$ and $\delta -$ , and $d$ is this distance between the centers of the positive and negative charges.