Scientists Say: Isotope

This is a variety of an element that differs in its number of neutrons

This image shows three isotopes of hydrogen. Each has one proton (purple) but a different number of neutrons (grey).

roxanabalint/istockphoto

Isotope (noun, “EYE-so-tope”)

An isotope is a form of an element. An element is defined by its number of protons. But each atom of an element can differ in its number of neutrons — neutrally-charged particles in the nucleus.

Some isotopes are more stable than others. Less stable isotopes may decay, or break apart, over time. For many of these unstable isotopes, scientists know how fast they decay. That is useful information. If scientists measure the amount of an isotope in something like ancient bone, they can calculate out how old that item is. 

In a sentence

Scientists study isotopes from the moon to study where our planet’s tagalong came from.

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Correction (May 2, 2017, 4:30PM EST): The image on this post has been changed to reflect the neutral charge of neutrons. 

Bethany is the staff writer at Science News for Students. She has a Ph.D. in physiology and pharmacology from Wake Forest University School of Medicine.

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