Electric Dipole Moment: Definitions, Formula, Significance, How to Calculate, and Unit

Dipole Moment Formula Overview 

A dipole moment describes the existence of electric or magnetic charges in the vicinity of a system. The dipole moment is the mathematical product of the separation of these electric or magnetic charges. Since molecules with more than two polar connections are not symmetrical, they include dipole moments. 

What is an Electric Dipole Moment?

An electric dipole is defined as a pair of objects with equal and opposing charges that are separated by a limited distance. 

For Example- Two charges of identical magnitude 'Q' separated by a distance "D." In this case, we suppose that the first charge is negative while the second charge remains positive. This specific combination is known as an electric dipole. As a result, we may say that an electric dipole is generated when equal and opposing charges are separated by an ensured distance.

Electric Dipole Moment Formula

The electric dipole moment formula for a pair of equal and opposing charges is

What is a Dipole Moment?

Dipole moments develop as a result of an electronegativity mismatch between two chemically linked atoms. A bond dipole moment quantifies the polarity of a chemical connection formed by two atoms in a molecule. It is based on the notion of the electric dipole moment, which is a measurement of the separation of negative and positive charges in a system. Because it has both magnitude and direction, the bond dipole moment is a vector quantity.

It is worth noting that the symbols + and - denote the two electric charges that occur in a molecule that are equal in magnitude but have opposing signs. They are separated by a fixed distance, often represented by a "d”.

Dipole Moment Formula in Electric Field  

The two forces acting on the dipole ends cancel each other out as free vectors, but they act as separate points. As a result, it produces a torque on the dipole. Also, the dipole has a rotational action as a result of the torque. The magnitude of the torque (t) when considering the dipole centre is the total of the two forces times their respective distance arms, which is-

|t| = 2q |E|a sin q

    = |p||E| sin q

t = p × E     (expressed in newton-meter)

As a result, in the presence of a homogeneous electric field, a dipole tends to align itself parallel to the field in question. Other requirements must also be met for this to occur, such as orientation remaining at some non-zero angle designated as "q." Moreover, potential energy must be stored in the dipole at a preferred orientation ranging from q = 0 to q > 0.

What is Dipole Moment Formula?

A dipole moment is the product of the charge magnitude and the distance between the positive and negative charge centers. 

Dipole Moment (µ) = Charge (Q) * distance of separation ®

Mathematically,

It is measured in Debye units, which are indicated by the letter "D”. 

1 D = 3.33564 10⁻³⁰ C.m., where C stands for Coulomb and m stands for meter

In a chemical bond between two atoms with differing electronegativities, the bond dipole moment may be represented as follows-

μ= δ.d

Where the bond dipole moment is,

The magnitude of the δ⁺ and δ⁻ partial charges,

where d represents the distance between δ⁺and δ⁻.

The bond dipole moment (μ) is a vector variable that runs parallel to the bond axis. The arrows used to indicate dipole moments in chemistry start at the positive charge and stop at the negative charge. When two atoms with different electronegativities interact, the electrons tend to migrate from their original locations towards the more electronegative atom. The bond dipole moment can depict this electron movement.

Significance of Dipole Moment Formula

1. The study of the phenomena and behavior of the opposing charges existing around us, as well as how they behave when held at a distance, is the focus of electric dipole theory.
2. Positive and negative charge centers are usually found in the same location in most molecules. As a result, their dipole moment is zero. 
3. This class of molecule includes CO₂and CH₄. 
4. When an electric field is applied, they form a dipole moment.
5. There are times when the centers of negative and positive charges do not coincide in polar molecules. 
6. As a result, even in the absence of an electric field, they have a persistent electric dipole moment. This kind of molecule includes water molecules (H₂O).
7. In the presence or absence of electric fields, certain materials exhibit fascinating features and have crucial uses.

How to Calculate the Electric Dipole Moment Formula?

The following are some of the steps to calculate the electric dipole moment-

1. Step 1: Determine the size of one of the charges.
2. Step 2: Determine the separation between two charges.
3. Step 3: Calculate the dipole moment by multiplying the magnitude of one of the charges by the distance calculated in steps 1 and 2.

Unit of Dipole Moment Formula

The charge in the CGS system is given in esu, and the bond length is in cm. As a result, the dipole moment is measured in esu cm. The charge is in the order of 1010 esu, while the separation is in the order of 108 cm. As a result, the order is 1018 esu cm. This magnitude is known as 1. As a result, 

1 Debye = 1018 esu cm

The charge in the SI system is represented in coulombs and thelength in meters. As a result, the coulomb meter is the SI unit of dipole moment.

What is Dipole Moment Formula in Chemistry?

In chemistry, the dipole moment indicated the polar nature or polarity of the molecules. The dipole moment of molecules is defined as the product of charge and the distance between atoms in a chemical bond. If the bond distance l separates +q amount of positive charge from q amount of negative charge, then dipole moment of polar molecule = q l.

Dipole Moment Formula Chemistry

The following are some of the dipole moments of chemistry-

Dipole moment of HCl

The dipole moment of the HCl molecule is the same as the dipole moment of the HCl bond, which is 1.03D in the diatomic molecule of HCl.

Dipole moment of BeF₂

The dipole moment of a beryllium fluoride molecule is zero. BeF₂has a straight shape. Each bond's dipole moments cancel each other out, resulting in a net dipole moment of zero. This is because the bond dipole moments in the BeF2 molecule are equal in magnitude and opposite in direction.

Dipole moment of CO₂

The dipole moment of thetriatomic CO₂(carbon dioxide) molecule is zero. Because of the molecule's linear form, the dipole moment of the C=O bond (2.3D) on one side cancels out the dipole moment on the opposite side, resulting in a net zero dipole.

Dipole moment of H₂O

The dipole moment of a triatomic H₂O water molecule is 1.84D. The dipole moment is not zero due to the bent shape of the water molecule. This is due to the consequent dipole moments of two O-H bonds tilted at 104.5 degrees with two oxygen atom lone pairs.

Dipole moment of NH₃and BH₃

The dipole moment of tetra-atomic boron trihydride (BH₃) is zero, whereas that of ammonia (NH₃) is 1.49D. This is because BH₃has a symmetrical structure and the three B-H bonds are at a 120-degree angle to each other. Because the three bonds are on a single plane, their dipole moments cancel each other out, resulting in a net dipole moment of zero. NH₃, on the other hand, has a pyramidal structure with three N-H bonds and a single pair on the nitrogen atom. This results in a dipole moment of 1.49 D.

Dipole moment of NF₃and NH₃

Moreover, while both NH₃and NF₃molecules have three N-H bonds and a lone pair on nitrogen atoms, the resultant dipole moment of NF₃is smaller than that of NH₃. This is due to the fact that the dipole produced between the lone pair and the nitrogen atom varies in NH₃and NF₃molecules. Since fluorine is more electronegative than nitrogen, it will draw all of the shared electrons from nitrogen in the opposite direction from the net dipole moment. As a result, the dipole moment of NF₃diminishes. While nitrogen is more electronegative than hydrogen, it will draw all of the shared electrons from hydrogen in the same direction due to N-H bonding. As a result, the NH₃dipole moment rises.

Dipole moment of CH₄and CCl₄ 

The dipole moments of the CH₄(methane) and CCl₄(carbon tetrachloride) molecules are zero. These two molecules, CH₄and CCl₄, have a symmetrical tetrahedral configuration. As a consequence, dipole moments of C-H bonds in CH₄cancel out and result in zero dipole moments, and dipole moments of C-Cl bonds in CCl₄molecules cancel out and result in zero dipole moments.

Dipole moment of CH₃Cl

Even though the CH₃Cl (methyl chloride) molecule has a tetrahedral shape, its dipole moment is not zero. This is due to the fact that methyl chloride's structure is not symmetrical and the dipole moments of the bonds C-Cl and C-H are not equal. As a result, the corresponding dipole moment is 1.86 D.

Points to Remember

1. The dipole moment of a single bond in a polyatomic molecule is known as the bond dipole moment, and it differs from the molecule's overall dipole moment.
2. The dipole moment is symbolized in chemistry by a modest variant of the arrow sign. It has a cross in the positive center and an arrowhead in the negative center.
3. This arrow represents the molecule's change in electron density.
4. In the case of a polyatomic molecule, the dipole moment is the vector sum of all bond dipoles present in the molecule.
5. It is a vector quantity, which means it has both magnitude and defined directions.
6. Because it is a vector quantity, it can also be 0 because the two opposing bond dipoles can cancel each other out.
7. It is typically represented by a tiny arrow with its tail in the negative center and its head in the positive center.