Question

what kinds of intermolecular forces are there? order them in increasing strength.(methanol, ethanol, n-propanol, isopropanol, and acetone.)

Answer 1

Methanol, ethanol, n-propanol and isopropanol are alcohols.all 4 show similar forces. 1)H-bond is formed between hydrogen atom of one molecule and oxygen atom of another molecule. 2)dipole-dipole forces- due to the presence of polar OH group, a dipole exists i. e. There is a positive and negative end.

3))vander Wall's forces- These forces are the weakest forces and their magnitude increase with increase in surface area. These forces are also called london forces or dispersion forces.

The strength of intermolecular forces follows the order:

VanderWall's forces < dipole-dipole forces<H-bond

Acetone is a ketone.

The intermolecular forces present in this molecule is dipole-dipole forces because of highly polar carbonyl group.

vander Wall's forces are also present.

Increasing order of strength

vanderWall's forces< dipole-dipole forces

If we compare the strength of intermolecular forces in alcohols :methanol<ethanol<isopropanol<n-propanol

As R group gets larger, the magnitude of vanderWall's forces increases and so is the boiling point. Thus, the value of boiling point of alcohol indicates the strength of intermolecular forces. The combined effect of vanderWall's forces and H-bond increases the boiling point. n-propanol and isopropanol are isomeric alcohols. n-propanol is a primary alcohol having larger surface area while isopropanol being secondary alcohol has a compact structure. Thus, vanderWall's forces are stronger in propanol as compared to isopropanol.