Explain why water wets glass while mercury does not
Water wets glass while mercury does not because of their respective molecular structures and intermolecular forces.
Water (H2O) is a polar molecule, meaning it has a partial positive charge on the hydrogen atoms and a partial negative charge on the oxygen atom. Glass surfaces are also polar due to the presence of oxygen atoms. This polarity allows for strong attractive forces, called hydrogen bonding, between water molecules and the glass surface. As a result, water molecules are able to adhere to the surface of the glass and spread out, or wet the surface.
On the other hand, mercury (Hg) is a nonpolar molecule, as it consists of two mercury atoms bonded together. Nonpolar molecules do not have charges or partial charges, and therefore do not form strong attractive forces like hydrogen bonding. Glass surfaces do not have a strong affinity for nonpolar molecules, so the weak intermolecular forces between mercury molecules and the glass surface are not sufficient for the mercury to wet the glass. Instead, mercury tends to form cohesive droplets due to its low surface tension.
In summary, the polar nature of water and the nonpolar nature of mercury, along with the respective intermolecular forces, determine why water wets glass while mercury does not.