At diverging plate boundaries, earthquakes occurs as the plates pull away from each other. Volcanoes form between the plates, as magma rises upward from the underlying mantle. Second, two plates may come together, at a converging plate boundary. Two situations are possible at converging plate boundaries.
This is because oxygen (2.8.6) requires two electrons on its valence shell to attain stable configuration (2.8.8). Hydrogen (1) on the other hand requires one electron on its valence shell to attain stable configuration (2). Therefore in a covalent bond, it requires two hydrogen and one oxygen to share electrons and achieve stable configuration.