The Octet Rule
Atoms bond to have eight valence electrons.
About this topic
The octet rule says that atoms tend to gain, lose or share electrons until they have eight valence electrons, like the noble gases (two for hydrogen and helium). It explains why sodium forms Na+ and chlorine forms Cl−, and why oxygen typically forms two bonds.
Atoms with a full outer shell are in a low-energy, stable state, so they react to reach it. Metals in groups 1 to 3 lose electrons, non-metals in groups 15 to 17 gain electrons or share them, and carbon, with four valence electrons, shares four. The rule is a guideline, not a law. Exceptions include hydrogen with two, boron and beryllium with fewer than eight, and elements in period 3 and below, such as phosphorus and sulfur, which can have an expanded octet. Odd-electron molecules such as nitrogen monoxide cannot satisfy it either.
Example: in the ammonia molecule, nitrogen has five valence electrons and shares one with each of three hydrogens, giving three bonds and one lone pair, for a total of eight around nitrogen. In magnesium chloride, magnesium gives two electrons, one to each chlorine.
The rule helps predict formulas and Lewis structures quickly. A common error is applying it to hydrogen, which wants two, or to transition metals. Treat it as a first approximation and check against known compounds.
Key ideas
- Hydrogen needs two
- Exceptions exist
- Explains why noble gases are stable
Quick check
Use cases: where The Octet Rule helps
- Homework: review the key idea behind The Octet Rule before you start a problem set.
- Exam revision: use the quick check to test whether you can recall The Octet Rule without notes.
- Visual learning: play with the interactive lab to see how The Octet Rule changes when you adjust its inputs.
- Teaching a friend: explain The Octet Rule in your own words, then compare your version with the key ideas.
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Frequently asked questions
What is The Octet Rule?
Atoms bond to have eight valence electrons.
What will I learn in The Octet Rule?
Hydrogen needs two. Exceptions exist. Explains why noble gases are stable.
Is The Octet Rule part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the The Octet Rule lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study The Octet Rule?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.