Why do atoms form molecules? The quantum physics of chemical bonds explained

Why do atoms combine to form molecules? The quantum mechanics of chemical bonds and chemistry. How is it that we can have so many chemical substances with only about 100 relatively simple building blocks, called atoms? This is because atoms are rarely found alone. They are mostly found in combinations with other atoms, through the process of chemical bonding. Why does this happen? Why is the universe not full of just atoms floating around? The answer to this important question lies in understanding the role that energy plays in the formation of molecules, and its roots in quantum mechanics. All natural systems tend to adopt a state of lowest energy. A marble at the top of a hill has high potential energy due to gravity. If given the opportunity, it will roll naturally to the bottom of the hill where it will have a lower potential energy. The hydrogen atom by itself will be in its lowest energy state, called the ground state. But when a second hydrogen atom is introduced, some things