Look up and compare the normal boiling points and normal melting points of \(\mathrm{H}_{2} \mathrm{O}\) and \(\mathrm{H}_{2} \mathrm{~S}\). Based on these physical properties, which substance has stronger intermolecular forces? What kinds of intermolecular forces exist for each molecule?

We can find the normal boiling points and normal melting points of water (H₂O) and hydrogen sulfide (H₂S) in a chemistry reference book or online. For water (H₂O): - Normal boiling point: 100°C (212°F) - Normal melting point: 0°C (32°F) For hydrogen sulfide (H₂S): - Normal boiling point: -60.7°C (-77.3°F) - Normal melting point: -82°C (-115.6°F)

Comparing the normal boiling and melting points, we see that H₂O has much higher boiling and melting points than H₂S. This indicates that H₂O has stronger intermolecular forces, as more energy is required to break these forces and cause a phase transition (from solid to liquid or from liquid to gas).

There are several types of intermolecular forces, including London dispersion forces, dipole-dipole interactions, and hydrogen bonding. Water contains highly polar O-H bonds due to the difference in electronegativity between oxygen and hydrogen. The oxygen atom carries a partial negative charge, while the hydrogen atoms carry partial positive charges. This results in strong dipole-dipole interactions. In addition, water molecules can form hydrogen bonds (a particularly strong kind of dipole-dipole interaction) due to the presence of highly polar O-H bonds.

Hydrogen sulfide, like water, has polar S-H bonds due to the difference in electronegativity between sulfur and hydrogen. However, the S-H bond is less polar than the O-H bond in water, leading to weaker dipole-dipole interactions. Although hydrogen sulfide also contains polar S-H bonds, it does not exhibit hydrogen bonding because the sulfur atom is not as electronegative as the oxygen atom (hydrogen bonding typically occurs with more electronegative elements like oxygen, nitrogen, and fluorine). In summary, water (H₂O) has stronger intermolecular forces, mainly due to its ability to form hydrogen bonds, while hydrogen sulfide (H₂S) has weaker intermolecular forces due to its less polar bonds and the absence of hydrogen bonding.