What Are Some Examples of Atoms?

Atoms are fundamental units of matter that cannot be broken down by any chemical means.

What Makes Something an Atom?

The building blocks of atoms are positively charged protons, neutral neutrons, and negatively charged electrons. Protons and neutrons are similar in mass, while electrons are much smaller and lighter. Many atoms consist of a positively charged nucleus composed of protons and neutrons surrounded by a negatively charged cloud of electrons. At its most basic level, an atom is any particle of matter that contains at least one proton. Electrons and neutrons may be present, but aren't required.

Atoms may be neutral or electrically charged. An atom that carries a positive or negative charge is called an atomic ion.

Atoms of a single element that have different numbers of neutrons from one another are called isotopes.

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What Is an Atom?

By Anne Marie Helmenstine, Ph.D.

A single particle of any element listed in the periodic table is an atom. The number of protons present determines an atom's order in the periodic table, along with its name, symbol, and chemical identity.

Here are some examples of atoms:

• Neon (Ne)
• Hydrogen (H)
• Argon (Ar)
• Iron (Fe)
• Calcium (Ca)
• Deuterium, an isotope of hydrogen that has one proton and one neutron
• Plutonium (Pu)
• F^-, a fluorine anion
• Protium, an isotope of hydrogen

Atoms Versus Molecules

When atoms bond together, they become molecules. When the chemical symbol of a molecule is written out, you can distinguish it from an atom by the subscript following the element symbol, which indicates how many atoms are present.

For example, O is the symbol for a single atom of oxygen. On the other hand, O₂ is the symbol for a molecule of oxygen gas consisting of two oxygen atoms, while O₃ is the symbol for a molecule of ozone consisting of three oxygen atoms.

The symbol for water is H₂O. A water molecule contains two kinds of atoms. You can recognize this from the element symbols in the chemical formula. The two types of atoms are hydrogen atoms and oxygen atoms. In the case of water, each molecule contains two hydrogen atoms and one oxygen atom.

So, all molecules contain atoms, but they are not individual atoms. When you see an element name or an element symbol, you're know you're dealing with atoms.

What Is Not an Atom?

Another way to look at what is an example of an atom is to see examples of things that are not atoms.

• Atoms are units of matter, so by definition, anything that does not consist of matter is not an atom. Light, heat, dreams, and sound are not atoms.
• Parts of atoms not associated with a proton are not atoms. For example, an electron is not an atom. A neutron, even bonded to other neutrons, is not an atom.

Technically, ions, molecules, and compounds are all atoms. Usually, however, when someone talks about an atom they mean a single particle of an element. Most often, this means a neutral atom, which has an equal number of protons and electrons and lacks a net electrical charge.

Sources

• Einstein, Albert (1905). "Über die von der molekularkinetischen Theorie der Wärme geforderte Bewegung von in ruhenden Flüssigkeiten suspendierten Teilchen". Annalen der Physik (in German). 322 (8): 549–560.
• Heilbron, John L. (2003). Ernest Rutherford and the Explosion of Atoms. Oxford University Press. ISBN 0-19-512378-6.
• Holbrow, Charles H.; Lloyd, James N.; Amato, Joseph C.; Galvez, Enrique; Parks, M. Elizabeth (2010). Modern Introductory Physics. Springer Science & Business Media. ISBN 9780387790794.
• Pullman, Bernard (1998). The Atom in the History of Human Thought. Oxford, England: Oxford University Press. pp. 31–33. ISBN 978-0-19-515040-7.
• van Melsen, Andrew G. (2004) [1952]. From Atomos to Atom: The History of the Concept Atom. Translated by Henry J. Koren. Dover Publications. ISBN 0-486-49584-1.