The “lead” of a pencil is actually made of a substance called graphite which is made of carbon atoms. The picture shows a close-up of one carbon atom. A hydrogen atom has one proton as the nucleus and ...

As you move from left to right across the periodic table ... of the filled inner electron levels. These electrons screen or shield the outer electrons from the nuclear charge.

To the left of gold in the periodic table are two elements ... terms of the fundamental physical constants, such as the electron charge and Planck's constant. One proposal for replacing ...