Question

What’s More

Activity 1. Strength of IMFA and Physical Properties of

Covalent Compounds

For each pair of molecules, identify the one with the higher boiling point (BP), melting
point (MP), viscosity (V), surface tension (ST) and vapor pressure (VP). Briefly explain
your choice.

Answer 1

Covalent compounds means bond between non metals

Answer 2

The given pairs have the following properties:

• Pair 1: Methane (
  `CH_(4)`) vs. Carbon Tetrachloride (
  `CCl_(4)`)

BP, MP, V, ST - Higher in
`CCl_(4)`

VP - Higher in
`CH_(4)`

• Pair 2: Dihydrogen sulfide (
  `H_(2)S`) vs. Water (
  `H_(2)O`)

BP, MP, V, ST - Higher in
`H_(2)O`

VP - Higher in
`H_(2)S`

• Pair 3: Methanol (
  `CH_(3)OH`) vs. Ethanol (
  `CH_(3)CH_(2)OH`)

BP, MP, V, ST - Higher in
`CH_(3)CH_(2)OH`

VP - Higher in
`CH_(3)OH`

• Pair 4: Acetic acid (
  `CH_(3)COOH`) vs. Acetone (
  `CH_(3)COCH_(3)`)

BP, MP, V, ST - Higher in
`CH_(3)COOH`

VP - Higher in
`CH_(3)COCH_(3)`

Reasons for the above observations:

• 
  `CCl_(4)` has a higher molecular weight and stronger London dispersion forces due to its larger chlorine atoms compared to methane's hydrogen atoms. This leads to higher boiling point, melting point, viscosity and surface tension. Stronger intermolecular forces make it harder for
  `CCl_(4)` molecules to escape the liquid phase into the vapor phase, thus making the vapor pressure lower.

• Water molecules can form hydrogen bonds, which are much stronger than London dispersion forces present in
  `H_(2)S`. Hydrogen bonding also creates a stronger attraction between molecules at the surface. This results in higher boiling point, melting point, viscosity and surface tension in
  `H_(2)O`. Stronger intermolecular forces make it harder for
  `H_(2)O` molecules to escape the liquid phase into the vapor phase, contributing to lower vapor pressure.

• Ethanol has a higher molecular weight and stronger London dispersion forces due to its longer carbon chain compared to methanol. This leads to higher boiling and melting points and lower vapor pressure. Stronger London dispersion forces lead to greater intermolecular attractions and resistance to flow, resulting in higher viscosity and surface tension.

• Acetic acid can form hydrogen bonds, which are much stronger than the London dispersion forces present in acetone. This leads to higher boiling and melting points and lower vapor pressure. Hydrogen bonding leads to stronger intermolecular attractions and resistance to flow. This results in higher viscosity and surface tension.

The intermolecular forces and bonds are the factors deciding the physical properties of covalent compounds.