Can anyone please define what are Polar and Non polar solvents?

1 Answer
Oct 18, 2016

#"Polarity"# means charge separation...........


And thus a polar solvent is a solvent which possesses charge separation, and, maybe, the ability to #"solvate"#, i.e. dissolve, ions and other polar materials.

Water is the classic polar solvent, because the oxygen atom tends to polarize electron density towards itself, and denudes the bound hydrogens of electron density: #""^(delta+)H-^(delta-)O-H^(delta+)# is the classic representation of this polarization, and this leads to the phenomenon of hydrogen bonding. Other polar solvents include #NH_3#, and #HF#.

I am trying to think of some metric, something measurable, with which we can measure the polarity. Large molecular dipole moments and high dielectric constants are usually possessed by polar solvents (certainly by those solvents above). The hydroxyl group on the lower alcohols, methanol, and ethanol, confers some degree of polarity.

On the other hand, solvents composed of atoms that have small differences in electronegativity, e.g. #C-H# and #C-C# are generally non-polar. Hexanes is a prime example of a non-polar solvent. Longer chain alcohols, while they possess an hydroxyl group, become increasingly non-polar as their chain length increases, and the influence of the hydroxyl group is overshadowed by the hydrophobic chain.