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 small but heavy nucleus at its center. A cloud of tiny, fast-moving electrons orbit around the nucleus. The nucleus contains protons and neutrons. Most atoms have about as many neutrons as protons. A "normal" atom has the same number of electrons and protons.

The animation of an atom on this page is NOT to scale. In a real atom, the protons, neutrons, and electrons are very tiny compared to the distance between the nucleus and the electrons. Most of an atom is empty space. Atoms are incredibly small. They have sizes between 60 and 500 picometers (a picometer is 10-12 meters, or one trillionth of a meter!). The nucleus of an atom is about 100,000 times smaller than the whole atom. Almost all (more than 99%) of the mass of an atom is in the nucleus.

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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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA