Scientists Say: Molecule

This is two or more atoms bonded together

This is an artist’s drawing of water molecules. Each molecule has one oxygen atom in the center, with a hydrogen atom bound to it on either side.

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Molecule (noun, “MOLL-eh-kewl”)

A molecule is usually two or more atoms held together with chemical bonds.

Molecules can be homonuclear. That means they contain atoms of only one element. The oxygen we breathe, for example, is a molecule of two oxygen atoms — O2. Other molecules are heteronuclear — made of more than one element. A molecule of water — H2O — is made of two hydrogen atoms bonded to one oxygen atom.

Molecules make up your own body, the air we breathe, everything living around us. A molecule is the smallest particle of a substance that still has all the chemical properties of that substance. For example, a single molecule of water — H2O — has all the properties of water. But split it apart into its atoms, and it will not be water anymore.

Smaller molecules can join together to make up large ones. A single strand of DNA, for instance, is one large molecule. That one molecule of DNA is made from many smaller molecules, including sugars and phosphates. Take apart a DNA molecule and it will not be able to do what DNA does — provide the instructions cells need to survive.

Put together, the atoms in most molecules have a neutral electrical charge — neither positive nor negative. But some atoms — such as helium — don’t have any electrical charge, even by themselves. Some people count these single atoms as molecules too. And some molecules do have an electrical charge. These charged molecules are called ions.

In a sentence

In your armpits, bacteria turn an odorless molecule in our sweat into one that truly stinks.

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Bethany Brookshire is the staff writer at Science News for Students. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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