Intermolecular-Forces-Worksheet-Key-covalen bonds-and ... - Free Printable

Let’s go step by step to solve this worksheet. We’ll look at each question and figure out the strongest intermolecular force for each substance, then explain boiling point order based on those forces.

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Question 1: Identify the strongest intermolecular force in pure samples

We need to know what kind of molecule each is — polar? nonpolar? can it hydrogen bond?

- SO₂: Bent shape → polar → dipole-dipole forces (strongest here)
- H₂O: Has H bonded to O → can form hydrogen bonds → strongest = hydrogen bonding
- CH₂Cl₂: Polar molecule (C-H and C-Cl bonds don’t cancel) → dipole-dipole
- SCO: Linear but not symmetric → polar → dipole-dipole
- PCl₃: Trigonal pyramidal → polar → dipole-dipole
- SO₃: Trigonal planar, symmetrical → nonpolar → only London dispersion forces

✔ All match the red answers given.

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Question 2: Strongest IMF in condensed phases + explanation

a. Cl₂ – Two same atoms → nonpolar → only London dispersion
b. CO – C-O bond is polar → molecule is polar → dipole-dipole (stronger than London)
c. SO₂ – Bent → polar → dipole-dipole
d. CH₂Cl₂ – Polar, no H-bonding → dipole-dipole
e. HF – H bonded to F → hydrogen bonding (strongest possible here)
f. CH₃-O-CH₃ (dimethyl ether) – Oxygen in middle, H not attached to O → no H-bonding → polar → dipole-dipole

All explanations are correct as written in red.

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Question 3: Boiling point order – propane, dimethyl ether, ethanol

Boiling point depends on strength of intermolecular forces:

Strongest forces → harder to pull molecules apart → higher boiling point

Order of IMF strength:
London dispersion < dipole-dipole < hydrogen bonding

Now analyze each:

- Propane (CH₃CH₂CH₃): Only C and H → nonpolar → only London dispersion → weakest → lowest bp
- Dimethyl ether (CH₃OCH₃): Has oxygen → polar → dipole-dipole → stronger than London → medium bp
- Ethanol (CH₃CH₂OH): Has OH group → H bonded to O → can form hydrogen bonds → strongest → highest bp

So order from lowest to highest boiling point:

propane < dimethyl ether < ethanol

Reason: As IMF strength increases, more energy (heat) is needed to separate molecules → higher boiling point.

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Final Answer:

1.
- SO₂: dipole-dipole forces
- H₂O: hydrogen bonds
- CH₂Cl₂: dipole-dipole forces
- SCO: dipole-dipole forces
- PCl₃: dipole-dipole forces
- SO₃: London dispersion forces

2.
a. Cl₂: London dispersion — nonpolar molecule
b. CO: dipole-dipole — polar molecule
c. SO₂: dipole-dipole — bent, polar
d. CH₂Cl₂: dipole-dipole — polar, no H-bonding
e. HF: hydrogen bonding — H bonded to F
f. CH₃OCH₃: dipole-dipole — polar, no H-bonding

3.
Boiling point order (lowest to highest):
propane < dimethyl ether < ethanol
Reason: Propane has only London forces, dimethyl ether has dipole-dipole, ethanol has hydrogen bonding — stronger forces mean higher boiling point.