The force of attraction exists between each and every single minute particle in the universe. The attraction is the cause of bonding in the chemicals, the attraction is the key for the magnetic field in physics and the simple gravity concept too works on attraction forces. Hence we can say that attractional forces exist between those particles which have charges or charged particles. In a substance, where the difference in the charges or separation of charges is seen there exist dipole moment.
Dipole moment arises in ionic bond as well as a covalent bond due to the difference in electronegativity among 2 chemically bonded atoms.
A dipole moment in a chemical bond is a measure of the polarity between 2 atoms in a molecule. This concept also involves the concept of electric dipole moment, which is a measure of the separation of positive and negative charges in a system. Electronegativity gives the measure of the tendency to pull a bonding pair of electrons towards the atom.
It is defined as the product of the magnitude of the charge and the distance between the center of positive/negative charge. It is represented by a symbol . The dipole moment is a vector quantity since it possesses both magnitude and direction.
An example describing the dipole moment in hydrochloric acid (HCl) molecule is as shown below.
represent the 2 electric charges that are witnessed in a molecule which are equal in magnitude but are of opposite signs. It is assumed that the charges are separated by the distance ‘d’. The dipole moment is mathematically represented as.
It is measured in Debye units denoted by ‘D’.
Where 1 D = 3.33564 × 10-30 C.m
C = Coulomb
m = distance in meter
Bond dipole moment in a chemical bond between two atoms of different electronegativities can be expressed as:
μ = bond dipole moment
𝛿 = magnitude of the partial charges 𝛿+ and 𝛿–
d = distance between 𝛿+ and 𝛿–
For the diatomic atoms, there shall exist only single or multiple bonds. For polyatomic molecules, there exist more than one bond. The total molecular dipole moment of the polyatomic molecule is calculated as the vector sum of individual bond dipole moments.
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