valence electron


noun Chemistry.

an electron of an atom, located in the outermost shell (valence shell) of the atom, that can be transferred to or shared with another atom.

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Origin of valence electron

First recorded in 1925–30
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

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What are valence electrons?

A valence electron is a negatively charged particle, located in the outermost shell of an atom, that can be transferred to or shared with another atom.

Valence (or valency) is an atom or group of atoms’ ability to chemically unite with other atoms or groups. Electrons are negatively charged subatomic particles surrounding the nucleus of an atom in shells. Valence electrons, then, are electrons in the outermost shell of the atom that determine an atom’s or group’s ability to bond with others.

In chemistry, a group refers to two or more atoms that are specifically arranged. Groups are also called radicals. Free radicals are unstable, highly reactive atoms or molecules that have unpaired valence electrons.

Valence electrons, bonding, and chemistry

Atoms may be teeny-tiny, but they have a lot going on beneath the surface. During the early 1900s, Gilbert N. Lewis (an American chemist and professor at University of California, Berkeley) significantly contributed to our understanding of valence electrons.

Some fundamentals: atoms are made up of neutrons, protons, and electrons. The nucleus (or the center of an atom) consists of neutrons and protons. Electrons surround the nucleus in shells. The shell closest to the nucleus can hold two electrons. The second shell can hold up to eight electrons, the third up to 18. (Different elements have different numbers of shells, each shell can hold only a fixed number of electrons, and there’s a formulaic way to determine that number).

Atoms—perhaps not unlike people?!—have one primary goal: to become stable. When the outer shell around an atom is filled with valence electrons, the atom is stable and doesn’t need to interact with other atoms to find stability. This is why elements like neon and argon don’t really react with other elements (because their outermost shell is naturally full with eight valence electrons).

So, what do atoms do if their outermost shell isn’t completely filled with valence electrons? They bond with other unstable atoms! There are two basic kinds of bonds:

The first kind is called a covalent bond. Covalent bonds happen when two atoms bond together by sharing valence electrons. One example of a covalent bond is a hydrogen bond (or H₂). A single hydrogen atom only has one outer shell and one valence electron. Remember, the first shell can hold two electrons, so hydrogen is naturally unstable. To fix this, a hydrogen atom will share a valence electron from another hydrogen atom so they both find stability.

The second kind of bond is an ionic bond. When one atom gains a valence electron while another atom loses a valence electron, that’s called an ionic bond. Ionic bonds tend to be stronger than covalent bonds. Sodium fluoride (NaF) is a common example of a compound formed by an ionic bond. Sodium has only one valence electron in its third shell while fluorine has seven valence electrons in its second shell (sodium doesn’t have a third shell). When they bond, sodium “gives” its valence electron to fluorine so they both can have eight valence electrons in their outer shells and be stable.

Did you know ... ?

When you brush your teeth in the morning, give thanks to sodium fluoride—and its shared valence electrons—in your toothpaste for fighting cavities. And, the next time you see a rocket soaring into space, know that there’s liquid hydrogen bonds fueling it.

What are real-life examples of valence electrons?

Here is a video explaining and visualizing how valence electrons work. They are tough concept, we know!

What other words are related to valence electron?

Quiz yourself!

_________ and ___________ bonds can occur when the outer shell of an atom isn’t completely filled with valence electrons.

Scientific definitions for valence electron

valence electron

An electron in one of the outer shells of an atom that can participate in forming chemical bonds with other atoms.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.