What is the effect of dipole moment on Melting and Boiling Points?
Dipole moment quantifies the term 'polarity'. Higher dipole moment means that the polarity of the molecule is higher (permanent positive and negative poles are present in the molecule) and hence attractive interatomic forces between the atoms is higher making the bonds stronger. A liquid boils when the kinetic energy of the molecules overcome the inter atomic forces between them. If the polarity is more(bonds are stronger), higher energy is required to overcome the cohesive forces and hence the boiling point is higher.
Hence higher the dipole moment, the higher is the boiling point.
For example, Propane(CH3CH2CH3) having molecular mass 44 amu and dipole moment of 0.1 has boiling point of 231 K whereas, acetaldehyde(CH3CHO) having molecular weight 44 amu and dipole moment of 2.7 has boiling point of 294 K.
Melting point is the temperature at which a solid phase changes to liquid phase. It is a solid state property and hence is effected by properties of solid phase such as amorphous or crystalline structure, symmetry, polymorphism, allotropy, etc more than the intermolecular forces that are acting upon it.
Hence higher the dipole moment, the higher is the boiling point.
For example, Propane(CH3CH2CH3) having molecular mass 44 amu and dipole moment of 0.1 has boiling point of 231 K whereas, acetaldehyde(CH3CHO) having molecular weight 44 amu and dipole moment of 2.7 has boiling point of 294 K.
Melting point is the temperature at which a solid phase changes to liquid phase. It is a solid state property and hence is effected by properties of solid phase such as amorphous or crystalline structure, symmetry, polymorphism, allotropy, etc more than the intermolecular forces that are acting upon it.