Hydrogen fluoride (HF) has a lower viscosity than water (H2O) because the intermolecular forces between HF molecules are weaker than the intermolecular forces between H2O molecules. This is because HF is a hydrogen-bonded liquid, while H2O is a covalent-bonded liquid.
In a hydrogen-bonded liquid, the molecules are held together by hydrogen bonds. Hydrogen bonds are strong intermolecular forces that form when a hydrogen atom in one molecule is bonded to a highly electronegative atom in another molecule. In HF, the hydrogen atom is bonded to a fluorine atom, which is a highly electronegative atom.
In a covalent-bonded liquid, the molecules are held together by covalent bonds. Covalent bonds are strong intermolecular forces that form when two atoms share electrons. In H2O, the two hydrogen atoms are covalently bonded to the oxygen atom.
The hydrogen bonds in HF are not as strong as the covalent bonds in H2O. This is because the fluorine atom is more electronegative than the oxygen atom. This means that the fluorine atom pulls the electrons in the hydrogen bond more strongly than the oxygen atom does. This makes the hydrogen bonds in HF weaker than the hydrogen bonds in H2O.
The weaker hydrogen bonds in HF result in a lower viscosity than the stronger hydrogen bonds in H2O. This means that HF flows more easily than H2O.
