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.
1 The number of electrons in an atom is the same as the number of protons in the atom. 2  That is because atoms are charge neutral, and protons have a charge of +1 while electrons have a charge of -1 so there must be the same number of each in order for the whole atom to be charge neutral.