Most atoms are found in combination with others. When atoms were formed, it was too hot for the electrons to be localized around a nucleus. Only when the surrounding temperature cooled down enough could the electrons stay. This tells us that the energies of keeping electrons around a nucleus are much smaller than the energies associated with the nucleus or the formation of electrons to begin with. It is the lower energies that permit electrons to be bound to a nucleus that define the conditions that we may exist in, because groups of atoms stay together, as molecules or solids for instance, only by the bonding of their electrons.
Electrons are the glue that holds groups of atoms together .
Electron shells and chemical bonding Let's review the nature of the atom from the point of view of the electrons. The atom is mainly low-density space with a very dense, small nucleus that defines its center. Electrons are located around the nucleus. These electrons can be classified in terms of shells that correspond to the rows in the periodic table. Each shell can fit a certain number of electrons, depending upon how far away from the nucleus it is.