Evaporating water (image 3 of 3). Molecular graph- ic of evaporating water molcules. Water molecules have one oxygen atom (light blue) & 2 hydrogen atoms (white). Each molecule is neutral, but the oxygen has a small negative charge & the hydrogens are slightly positive. The hydrogens are attracted to oxygens in nearby molecules, forming weak hydro- gen bonds (dark blue). Above 0 degrees celsius some molecules have enough thermal energy to break the hydrogen bonds, & so evaporate to form a vap-our. More bonds break with rising temperature, causing water to boil at 100 degrees celsius. (See also A504/062 for ice & A504/063 for liquid water).