the oxygen atom is very electronegative The high electronegativity of the oxygen atom is the reason that oxygen gas (O2) is such a good oxidizing agent (why it can oxidize so many compounds). The two atoms of the oxygen molecule (O2) share their electrons equally but, for example, when oxygen reacts with the hydrogen from methane, forming water, the electrons of the covalent bonds spend more time near the oxygen than the hydrogen. In effect, each oxygen atom has partially "gained" electrons, so the oxygen molecule has been reduced. Because oxygen is so electronegative, it is one of the most potent of all oxidizing agents. Energy must be added to pull an electron away from an atom, just as energy is required to push a ball uphill. The more electronegative the atom (the stronger its pull on electrons), the more energy is required to take an electron away from it. An electron loses potential energy when it shifts from a less electronegative atom toward a more electronegative one, just as a ball loses potential energy when it rolls downhill. A redox reaction that moves electrons closer to oxygen, such as the burning (oxidation) of methane, therefore releases chemical energy that can be put to work. Fats are better electron donors to oxygen than are sugars. Fats contain more hydrogen and less oxygen than sugars and it is the transfer of electrons from good donors, such as
hydrogen atoms, to good acceptors, such as oxygen, that provides the energy in respiration. |