In the molecule H2O, the electron configuration for H is 1s1, and for oxygen the electron configuration is 1s22s22p4 . The ratio of hydrogen to oxygen is 2 to 1, so each hydrogen contributes one electron to the oxygen atom, which needs two electrons to complete its outer most shell. The video shows two H atoms approaching the O atom to form two covalent bonds. The covalent bond is formed when the 1s orbital on H overlaps with a 2p orbital on O. However, using atomic orbitals on the oxygen atom would result in a H-O-H bond angle of 90 degrees. This differs from the 105 degree H-O-H bond angle that is experimentally determined for H2O.