Octet Rule Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Octet Rule.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

A chemical bonding principle stating that atoms tend to gain, lose, or share electrons in order to achieve a stable configuration of 8 electrons in their outermost shell, resembling the electron arrangement of the nearest noble gas.

8 is the magic number. Atoms 'want' a full outer shell like noble gases.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: The octet rule explains why atoms form the number and type of bonds they do.

Common stuck point: Hydrogen follows the 'duet rule' (2 electrons). Some elements break the octet rule.

Sense of Study hint: When using the octet rule to predict bonding, count valence electrons. First determine how many valence electrons each atom has. Then figure out how many more each needs to reach 8 (or 2 for hydrogen). Finally, atoms will share, gain, or lose electrons to satisfy the octet — the number of bonds an atom forms equals 8 - \text{valence electrons} for nonmetals.

Worked Examples

Example 1

easy
State the octet rule and explain why atoms tend to follow it.

Solution

  1. 1
    The octet rule states that atoms tend to gain, lose, or share electrons until they have 8 electrons in their outermost shell (valence shell).
  2. 2
    This configuration matches the electron arrangement of the noble gases, which are extremely stable.
  3. 3
    Having a full outer shell (8 electrons) represents the lowest energy state, so atoms naturally tend toward this configuration through chemical bonding.

Answer

\text{Atoms seek 8 valence electrons for noble gas stability.}
The octet rule is a guiding principle in chemistry that explains why atoms form bonds. It applies primarily to main-group elements in periods 2 and 3. Hydrogen is an exception — it needs only 2 electrons (a duet).

Example 2

medium
Use the octet rule to explain why sodium forms \text{Na}^+ and chlorine forms \text{Cl}^- when they react to form NaCl.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

medium
Use the octet rule to explain why oxygen forms two covalent bonds in a water molecule (\text{H}_2\text{O}).

Example 2

hard
Identify two exceptions to the octet rule and give a specific molecular example of each.
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Background Knowledge

These ideas may be useful before you work through the harder examples.

valence electron