text: There are certain principles that apply to calculate the strength of intermolecular attraction particularly at surface of a liquid.\n\nAs much the electronegativity within a molecule, it forms stronger polar molecule.\n\nAs much the number of polar bonds in a molecule, it makes stronger polar molecule.\n\nAs much the polarity of a molecule, it forms stronger inter-molecular bonds (often H-bond).\n\nIn case of of water Oxygen forms two bonds with Hydrogen so its polarity is higher than ethanol where only one H-O bond is formed.\nThis makes water more polar than ethanol and so stronger inter-molecular bond exist in water.\n\nAt surface of a liquid the forces of inter-molecular forces are disbalanced because of absence of molecules on the upper side. \nThis equally applies in all liquids however it affects surface attraction (surface tension) as compaired to other molecules within the liquid that is why surface tension is separately referred.\n\nNote: If you do not follow in first reading please do it again and you will understand easily.