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 atomic number of an element is equal to the number of protons in the nucleus of its atom. The atomic number is also known as proton number of the element. Further, in an atom, number of protons is equal to the number of electrons. Hence, atomic number is also equal to the number of electrons in an atom of the element. Thus,