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.
The number of protons and electrons in an atom or molecule determines its charge and whether it is a neutral species or an ion. This worked chemistry problem demonstrates how to determine the number of protons and electrons in an ion. For atomic ions, the key points to keep in mind are: A neutral atom has the same number of protons and electrons. This number is the atomic number of the element. A positively-charged ion or cation has more protons than electrons. The proton number is the atomic number of the element, while the electron number is the atomic number minus the charge.