Octet Rule
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Printed: August 14, 2015
AUTHOR
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C HAPTER
Chapter 1. Octet Rule
1
Octet Rule
• State the octet rule.
• Use the octet rule to predict outcomes of chemical reactions.
How are electrons organized in atoms?
Graduations are exciting events in one’s life. The processional, the ceremonies, even the speeches can be handled
because this marks the end of a stage of life and the beginning of another one. The ceremony itself is challenging for
those organizing it. There are just enough seats on the stage for the graduates. How do you avoid getting too many
people in a row and not enough in the next row? Someone is stationed at the end of the row to count the students as
they enter. Only so many are allowed to go into a row, and then you begin to fill the next row. Electrons in atoms
behave the same way. There are rules that determine where electrons go in compounds.
Octet Rule
The noble gases are unreactive because of their electron configurations. The noble gas neon has the electron
configuration of 1s2 2s2 2p6 . It has a full outer shell and cannot incorporate any more electrons into the valence shell.
The other noble gases have the same outer shell electron configuration even though they have different numbers of
inner-shell electrons.
American chemist Gilbert Lewis (1875-1946) used this observation to explain the types of ions and molecules that
are formed by other elements. He called his explanation the octet rule. The octet rule states that atoms tend
to form compounds in ways that give them eight valence electrons and thus the electron configuration of a noble
gas. An exception to an octet of electrons is in the case of the first noble gas, helium, which only has two valence
electrons. This primarily affects the element hydrogen, which forms stable compounds by achieving two valence
electrons. Lithium, an alkali metal with three electrons, is also an exception to the octet rule. Lithium tends to
lose one electron to take on the electron configuration of the nearest noble gas, helium, leaving it with two valence
electrons.
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FIGURE 1.1
Electron configuration of neon atom.
There are two ways in which atoms can satisfy the octet rule. One way is by sharing their valence electrons with
other atoms. The second way is by transferring valence electrons from one atom to another. Atoms of metals
tend to lose all of their valence electrons, which leaves them with an octet from the next lowest principal energy
level. Atoms of nonmetals tend to gain electrons in order to fill their outermost principal energy level with an octet.
Summary
• Atoms form compounds in ways that give them eight valence electrons.
• Metals tend to lose electrons to achieve this configuration.
• Nonmetals tend to gain electrons to achieve this configuration.
Practice
Questions
Use the link below to answer the following questions:
http://www.mikeblaber.org/oldwine/chm1045/notes/Bonding/Except/Bond08.htm
1.
2.
3.
4.
Do most elements follow the octet rule?
How does hydrogen violate the octet rule?
Does sulfur always follow the octet rule?
What are free radicals?
Review
Questions
1.
2.
3.
4.
What is the electron configuration of a noble gas?
Why is this configuration important?
How do metals change to obey the octet rule?
How do nonmetals change to obey the octet rule?
• octet rule: Atoms tend to form compounds in ways that give them eight valence electrons and thus the electron
configuration of a noble gas.
References
1. Image copyright Gennadiy Titkov, 2014. http://www.shutterstock.com .
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Chapter 1. Octet Rule
2. CK-12 Foundation - Joy Sheng. .
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