Why Is Milk White?: & 200 Other Curious Chemistry Questions (2013)
8. Chemistry in the World
What do electrons do?
Electrons jump away from one another. That one fact explains most of electricity. If you push more electrons into a wire, they all push against one another and will move toward the place where there is the least pressure. We call that pressure voltage. A current is simply how many electrons are moving past a particular point in a second. Electrical power is how much pressure there is, multiplied by the amount of current.
In chemistry, electrons are what hold molecules together. Electrons are attracted to the positive charges at the center of atoms, but only specific numbers of electrons can fit in each energy-level shell around the nucleus.
If an atom has an empty spot in an energy level, and another atom has an electron in an otherwise empty energy level, that lone electron can fall into the empty space in the other atom’s shell, and the two atoms will stick together, because both nuclei will be pulling on that one electron.
This also works if there is more than one empty slot or more than one extra electron. The electrons will fall into the energy level as close to a nucleus as possible, no matter which atom it is in. So an oxygen atom, which has two empty slots in its shell, can take the lone electron from two hydrogen atoms and make a molecule of water. By sharing electrons in this way, the electrons can fall into the lowest energy level, closest to the nucleus.
In metals, the outer energy shells of the atoms merge into one big, empty slot, and the outer electrons can move around freely. In atoms like chlorine, the empty slot is so close to the nucleus that the electron spends most of its time near the chlorine atom and little time around the atom it came from (for example, the sodium atom in a molecule of salt). This allows the molecule to dissolve easily in water, leaving a positive sodium ion and a negative chloride ion.