What do an orgasm, a multiplication problem and a photo of a dead body have in common? Each induces a slight, irrepressible expansion of the pupils in our eyes, giving careful observers a subtle but meaningful signal that thoughts and feelings are afoot. For more than a century, scientists have known that our pupils respond to more than changes in light.
Review. 1  Atoms have their electrons arranged in layers called shells. 2  In order to maintain electrical balance the number of electrons is equal to the number of protons in most elements.
Actually the proton and electron count of an atom are equal only when the atom is neutral in charge. The three atomic particles of an atom are the protons, which carry a positive charge, the electrons which carry a negative charge and the neutrons which have no charge.