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.
Protons and electrons are oppositely charged. Neutrons have no charge. This means the nucleus of an atom is always positively charged. An atom has a neutral overall charge because it has the same number of electrons as protons.Protons and neutrons have the same mass. Electrons have such a small mass that this can usually be taken as zero.eutrons have no charge. This means the nucleus of an atom is always positively charged. An atom has a neutral overall charge because it has the same number of electrons as protons. Protons and neutrons have the same mass. Electrons have such a small mass that this can usually be taken as zero.