We are asked to determine which substance has a stronger intermolecular force knowing the normal boiling points and melting points of H2O and H2S.
Recall that there are several types of intermolecular forces (IMF):
1. Ion-dipole interaction – occurs between an ion and a polar covalent compound; strongest IMF
2. Hydrogen bonding – occurs in compounds where hydrogen is directly connected to an electronegative element such as N, O, or F; 2nd strongest IMF
3. Dipole-dipole interaction – occurs between two polar covalent compounds; 3rd strongest IMF
4. Dispersion forces – occurs in all compounds and is the primary IMF exhibited by nonpolar compounds; weakest IMF
Compounds with strong intermolecular forces have high boiling points. This is because they require more energy to be able to break the bonds during the phase transition.
So, we need to identify which among the given compounds have the highest boiling and melting points.
Look up and compare the normal boiling points and normal melting points of H2O and H2S.
Based on these physical properties, which substance has stronger intermolecular forces?