The most abundant elements in ocean water are hydrogen and oxygen, the two elements that constitute the water molecule. Excluding the water molecule, the most abundant elements in ocean water are sodium and chlorine.
Ocean water is primarily made of water, which has the chemical formula H2O. It contains 109 moles per liter of hydrogen and 55.2 moles per liter of oxygen. Water acts as an excellent solvent, which explains the many ions present in ocean water. The most abundant of these ions are sodium, which is present at a concentration of 0.470 moles per liter, and chlorine, which is present at a concentration of 0.547 moles per liter.