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.
Now, in a neutral atom, the number of protons must be equal to the number of electrons, otherwise it would not be neutral. Basically, the definition is saying that in a neutral atom, the atomic number is equal to both the number of protons, and the number of electrons, because, well, they both are the same..