This image is a model of an atom
Windows to the Universe original animation by Randy Russell.


Atoms are the smallest size pieces that elements come in. Each atom has a central nucleus surrounded by a cloud of electrons. The nucleus contains one or more protons and usually about as many neutrons as protons. A neutral (electrically) atom has just as many (negatively charged) electrons as (positively charged) protons.

The animation shown here is NOT to scale. The distance between the nucleus and the electrons in an actual atom are much larger in comparison with the sizes of the protons, neutrons, and electrons. Most of an atom is empty space. Atoms are incredibly small, ranging in size from about 60 to 500 picometers (a picometer is 10-12 meters, or one trillionth of a meter). The nucleus of an atom is typically about 100,000 times smaller than the atom as a whole. Atoms have masses on the order of 10-27 to 10-25 kilograms. Almost all of an atom's mass (>99%) is in the nucleus; protons and neutrons are much more massive than electrons.

Sometimes two or more atoms "stick together" to form a molecule. Some molecules have atoms of just one type; for example, an oxygen molecule (O2) has two oxygen atoms. Other molecules combine different types of atoms. Methane (CH4) has one carbon atom and four hydrogen atoms.

Last modified September 15, 2010 by Randy Russell.

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