Valence Electrons
Ck12 Science
Say Thanks to the Authors
Click http://www.ck12.org/saythanks
(No sign in required)
To access a customizable version of this book, as well as other
interactive content, visit www.ck12.org
CK-12 Foundation is a non-profit organization with a mission to
reduce the cost of textbook materials for the K-12 market both in
the U.S. and worldwide. Using an open-source, collaborative, and
web-based compilation model, CK-12 pioneers and promotes the
creation and distribution of high-quality, adaptive online textbooks
that can be mixed, modified and printed (i.e., the FlexBook®
textbooks).
Copyright © 2015 CK-12 Foundation, www.ck12.org
The names “CK-12” and “CK12” and associated logos and the
terms “FlexBook®” and “FlexBook Platform®” (collectively
“CK-12 Marks”) are trademarks and service marks of CK-12
Foundation and are protected by federal, state, and international
laws.
Any form of reproduction of this book in any format or medium,
in whole or in sections must include the referral attribution link
http://www.ck12.org/saythanks (placed in a visible location) in
addition to the following terms.
Except as otherwise noted, all CK-12 Content (including CK-12
Curriculum Material) is made available to Users in accordance
with the Creative Commons Attribution-Non-Commercial 3.0
Unported (CC BY-NC 3.0) License (http://creativecommons.org/
licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated
herein by this reference.
Complete terms can be found at http://www.ck12.org/about/
terms-of-use.
Printed: November 9, 2015
AUTHOR
Ck12 Science
www.ck12.org
Chapter 1. Valence Electrons
C HAPTER
1
Valence Electrons
• Define valence electron.
• Be able to indicate valence electrons when given the electron configuration for an atom.
What makes a particular element very reactive and another element non-reactive?
A chemical reaction involves either electron removal, electron addition, or electron sharing. The path a specific
element will take depends on where the electrons are in the atom and how many there are.
TABLE 1.1: Electron Configurations of Second-Period Elements
Element Name
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
Symbol
Li
Be
B
C
N
O
F
Ne
Atomic Number
3
4
5
6
7
8
9
10
Electron Configuration
1s2 2s1
1s2 2s2
1s2 2s2 2p1
1s2 2s2 2p2
1s2 2s2 2p3
1s2 2s2 2p4
1s2 2s2 2p5
1s2 2s2 2p6
In the study of chemical reactivity, we will find that the electrons in the outermost principal energy level are very
important and so they are given a special name. Valence electrons are the electrons in the highest occupied principal
energy level of an atom. In the second period elements listed above, the two electrons in the 1s sublevel are called
inner-shell electrons and are not involved directly in the element’s reactivity or in the formation of compounds.
Lithium has a single electron in the second principal energy level and so we say that lithium has one valence electron.
1
www.ck12.org
Beryllium has two valence electrons. How many valence electrons does boron have? You must recognize that the
second principal energy level consists of both the 2s and the 2p sublevels and so the answer is three. In fact, the
number of valence electrons goes up by one for each step across a period until the last element is reached. Neon,
with its configuration ending in s2 p6 , has eight valence electrons.
Summary
• Valence electrons are the outer-shell electrons of an atom.
• Valence electrons determine the reactivity of an atom.
Practice
Use the link below to answer questions about valence electrons:
http://www.sciencegeek.net/Chemistry/taters/Unit3ValenceElectrons.htm
Review
Questions
1.
2.
3.
4.
5.
Define valence electron.
Define inner shell electron.
How many valence electrons are there in fluorine?
What are the 2s electrons in nitrogen?
How many inner shell electrons are there in beryllium?
• inner-shell electrons: Those electrons that are not in the outer shell and are not involved in the reactivity of
the element.
• valence electrons: The electrons in the highest occupied principal energy level of an atom.
References
1. User:Chemicalinterest/Wikipedia. http://commons.wikimedia.org/wiki/File:Cobalt_carbonate.JPG .
2