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.
If you take chemistry, you will learn about electrons. Electrons are the smallest of the particles that make up an atom, and they carry a negative charge. The number of protons and electrons is equal in each atom. The hydrogen atom, for example, has just one electron and one proton. The uranium atom, on the other hand, has 92 protons, and therefore, 92 electrons. The atom's atomic number is the number of protons in the atom, which by default is also the number of electrons. An electron is so small that it cannot be seen with the naked eye, but neither can the atom itself.