1.13 Relate the strength of London Dispersion Forces to relative melting and boiling points for the noble gases or simple diatomic molecules (H2, N2, O2, F2, Cl2, Br2, and I2).

How do London Dispersion Forces (LDF’s) affect melting and boiling points?

Stronger LDF = Higher melting and boiling points because more energy is needed to separate molecules.

Rank the noble gases (Ne, Kr, He, Rn, Xe, Ar) from lowest to highest boiling point.

• He (Weakest LDF, lowest boiling point)

• Ne

• Ar

• Kr

• Xe

• Rn (Strongest LDF, highest boiling point)

Trend: Larger noble gases have stronger LDF and higher boiling points.

Rank the diatomic molecules (N2, F2, I2, H2, Cl2, O2, Br2) from lowest to highest boiling point

• H2 (Weakest LDF, lowest boiling point)

• N2

• O2

• F2

• Cl2

• Br2

• I2 (Strongest LDF, highest boiling point)

Trend: Larger molecules have stronger LDF and higher melting/boiling points.

Why does I2 have a much higher boiling point than F2?

I2 has higher boiling point than F2 because its larger electron cloud creates stronger London Dispersion Forces, requiring more energy to overcome the intermolecular attractions.

Why do noble gases have lower boiling points compared to diatomic molecules?

Nobile gases exist as single atoms, so they have weaker LDF’s than diatomic molecules, which have larger surface areas for interaction.