Why is HF has lower boiling point than CsI, even though HF has hydrogen bond.
Does HF have higher boiling point than O2
CsI is an ionic compound, One must break the lattice energy of the crystal just to melt it, then overcome the forces of attraction between ions (much larger than H bonding forces).
According to Wikipedia, HF boils just below room temperature.
http://en.wikipedia.org/wiki/Hydrogen_fluoride
The boiling points of compounds are largely determined by the strength and type of intermolecular forces present. In the case of HF and CsI, the difference in boiling points can be attributed to the types of intermolecular forces they exhibit.
HF has a lower boiling point than CsI because although HF molecules can form hydrogen bonds, the strength of hydrogen bonding is weaker than the attractive forces between CsI ions. Hydrogen bonding occurs when a hydrogen atom is bonded to a highly electronegative atom (in this case, fluoride) and is attracted to another electronegative atom (also fluoride) in a neighboring molecule. While hydrogen bonding is stronger than other types of intermolecular forces (such as dipole-dipole interactions), it is weaker than the ionic bonds present in CsI.
CsI, on the other hand, is an ionic compound composed of cesium (Cs) cations and iodide (I) anions. Ionic compounds have high melting and boiling points due to the strong electrostatic forces between the positively and negatively charged ions. These forces require a significant amount of energy to overcome, resulting in higher boiling points compared to compounds without ionic interactions.
Regarding your second question, HF does indeed have a higher boiling point than O2. O2 is a diatomic molecule composed of two oxygen atoms. Oxygen molecules are held together by relatively weak double covalent bonds. The intermolecular forces present in O2 are primarily London dispersion forces, which are temporary and weak interactions between nonpolar molecules. As a result, O2 has a lower boiling point compared to HF, which exhibits stronger intermolecular forces due to hydrogen bonding.