H2O has a much higher boiling point than H2Se because of the difference in their intermolecular forces. H2O molecules are held together by hydrogen bonding, which is a strong intermolecular force. Hydrogen bonding occurs when a hydrogen atom in a molecule is bonded to a highly electronegative atom, such as oxygen or nitrogen. The electronegative atom pulls the electron cloud of the hydrogen atom towards itself, creating a partial positive charge on the hydrogen atom. This partial positive charge then attracts the partial negative charge on another electronegative atom, forming a hydrogen bond.
H2Se molecules, on the other hand, are held together by van der Waals forces, which are much weaker intermolecular forces. Van der Waals forces occur when the electron clouds of two molecules momentarily overlap, creating a temporary dipole. These dipoles then attract each other, forming a van der Waals force.
Because hydrogen bonding is a much stronger intermolecular force than van der Waals forces, H2O molecules are held together much more tightly than H2Se molecules. This means that it takes more energy to break the intermolecular forces between H2O molecules and cause them to boil. Therefore, the boiling point of H2O is much higher than the boiling point of H2Se.
In addition to hydrogen bonding, the difference in the boiling points of H2O and H2Se can also be attributed to the difference in their molecular masses. H2O has a molecular mass of 18 g/mol, while H2Se has a molecular mass of 80 g/mol. The heavier the molecule, the more energy it takes to break the intermolecular forces between its molecules and cause it to boil. Therefore, the heavier H2Se molecule has a higher boiling point than the lighter H2O molecule.
