Subatomic Parts of the Atom

From Faraday s and Arrhenius s work with ions, Irish physicist G. J. Stoney (1826-1911) realized there must be some fundamental unit of electricity associated with atoms. He named this unit the electron in 1891. Unfortunate, he had no means of supporting his idea with experimental proof. Evidence remained elusive until 1897, when English physicist J. J. Thomson (1856-1940) was able to show experimentally the existence of the electron. 

The concept of the atom—a particle so small that until recently it could not be seen even with the most powerful microscope—and the subsequent determination of its structure stand among the greatest creative intellectual human achievements. 

What is this tiny particle we call the atom The diameter of a single atom ranges from 0.1 to 0.5 nanometer (1 nm = 1 X 10 m). Hydrogen, the smallest atom, has a diameter of about 0.1 nm. To arrive at some idea of how small an atom is, consider this dot ( ), which has a diameter of about 1 mm, or 1 X 10 nm. It would take 10 million hydrogen atoms to form a line of atoms across this dot. As inconceivably small as atoms are, they contain even smaller particles, the subatomic particles, including electrons, protons, and neutrons. 

A scanning tunneling microscope shows an array of copper atoms. 

Cathode ray tube. A stream of electrons passes between electrodes. The fast-moving particles excite the gas inside the tube, creating a greenish glow between the electrodes. 

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