What is an Atom?

Atoms are the extremely small particles of which we, and everything around us, are made. There are 92 naturally occurring elements and scientists have made another 17, bringing the total to 109. Atoms are the smallest unit of an element that chemically behaves the same way the element does.

When two chemicals react with each other, the reaction takes place between individual atoms at the atomic level. The processes that cause materials to be radioactive to emit particles and energy also occur at the atomic level.

Atomic Structure

In the early 20th century, a New Zealand scientist working in England, Ernest Rutherford, and a Danish scientist, Niels Bohr, developed a way of thinking about the structure of an atom that described an atom as looking very much like our solar system. At the center of every atom was a nucleus, which is comparable to the sun in our solar system. Electrons moved around the nucleus in "orbits" similar to the way planets move around the sun. (While scientists now know that atomic structure is more complex, the Rutherford-Bohr model is still a useful approximation to begin understanding about atomic structure.)

Nucleus
contains protons and neutrons; together these are called "nucleons"

Neutrons
have no electrical charge, and like protons, are about 1800 times as heavy as an electron.

Protons
are positively charged particles. All atoms of an element (radioactive and non-radioactive) have the same number of protons. Protons and neutrons in the nucleus, and the forces among them, affect an atom's radioactive properties.

Electrons

The particles that orbit the nucleus as a cloud are called electrons. They are negatively charged and balance the positive electrical charge of the protons in the nucleus.
Interactions with electrons in the outer orbits affect an atom's chemical properties

 

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