Why is H2O a liquid but CO2 a gas ?
Strong intermolecular forces exist between the δ- oxygen atom in one water molecule and δ+ hydrogen atom in a neighbouring water molecule. This is called hydrogen bonding and is the strongest type of intermolecular force. Hydrogen bonding only occurs between a δ+ hydrogen atom and a δ- fluorine, oxygen and nitrogen atom hence HF, NH3 and H20 all exhibit hydrogen bonding and their bp’s/mp’s are far higher than expected in comparison to the other hydrides of their groups (restricted to Van der Waals, which increases with the number of electrons in a molecule). The greater the intermolecular forces, the more energy is required to overcome the bonds for the molecules to become liquids or gases. There is no hydrogen bonding in CO2. This has nothing to do with molecular mass.
You’d think so, wouldn’t you. But it’s not just the molecular weight that contributes to whether something is a liquiid or a gas at room temperature. In this case, a major factor is a kind of bonding between molecules, called hydrogen bonding. Oxygen is very electronegative, meaning that it doesn’t share well in forming a bond. (Bad oxygen!) Instead, it tries to grab most of the electrons in the two electron oxygen-hydrogen bond for itself most of the time. The result is that it develops a partial negative charge. This leaves the hydrogens in water with a partial positive charge. The resulting bond is “polarized” and the water molecule is polar. The answer to your question comes from how this affects the neighboring water molecules. Electrostatic (i.e. charge-based) interactions between the partially negative oxygen of one water molecule and the partially positive hydrogen of another water molecule form what’s called a hydrogen bond between the two molecules. Those bonds are weaker tha
