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 (valence) shell.
8 is the magic number. Atoms 'want' a full outer shell like noble gases.
Showing a random 20 of 50 problems.
Example 1
challenge
Phosphorus pentachloride PCl5 has 10 electrons around phosphorus. Reconcile this with the octet rule and identify why it is allowed.PCl₅: phosphorus has 10 electrons (expanded octet) — allowed because period-3 elements have d-orbitals
Example 2
easy
To reach an octet, will chlorine (7 valence electrons) gain or lose electrons? How many?Chlorine has 7 valence electrons — it gains 1 to reach the argon octet
Example 3
challenge
Use the octet rule to derive the formula of aluminum oxide from Al (3 valence e-) and O (6 valence e-).
Example 4
medium
Show how the octet rule predicts F2 (a single bond between two fluorines).
Example 5
easy
Magnesium has 2 valence electrons. To follow the octet rule, what does it do?Magnesium has 2 valence electrons — it loses both to form Mg²⁺ with a neon-like octet
Example 6
challenge
Predict the compound formed when calcium (2 valence e-) reacts with nitrogen (5 valence e-) using the octet rule.
Example 7
medium
Phosphorus and chlorine combine. Use the octet rule to predict the simplest compound (without expanding the octet).
Example 8
medium
Use the octet rule to predict the simplest compound between K and Br.
Example 9
easy
How does oxygen achieve an octet when it has 6 valence electrons?
Example 10
medium
Use the octet rule to explain why sodium forms Na+ and chlorine forms Cl− when they react to form NaCl.Sodium has 1 valence electron — it loses this to achieve the neon octet
Example 11
medium
Predict the formula for calcium chloride using the octet rule.
Example 12
easy
Fluorine has 7 valence electrons. To follow the octet rule, will it gain or lose, and how many?Fluorine has 7 valence electrons — it gains 1 to complete its octet
Example 13
medium
Why does SF4 violate the octet rule for sulfur, and why is this allowed?
Example 14
medium
Predict the most likely ion for nitrogen (5 valence electrons) using the octet rule, and explain the choice.Nitrogen has 5 valence electrons — it gains 3 to reach the neon octet, forming N³⁻
Example 15
medium
Will sulfur (6 valence e−) typically gain or lose electrons to satisfy the octet rule when forming an ion?
Example 16
easy
To reach an octet, will sodium (1 valence electron) gain or lose electrons? How many?Sodium has 1 valence electron — it loses this electron to achieve a noble-gas octet
Example 17
easy
Why do noble gases not readily form bonds, in octet-rule terms?
Example 18
medium
How many lone pairs of electrons does NH3 have on nitrogen?NH₃: nitrogen has 1 lone pair — 3 bonding pairs + 1 lone pair = 8 electrons (octet)
Example 19
medium
Why is the molecule NO (nitric oxide) an exception to the octet rule?
Example 20
hard
Explain why NO2 is an octet-rule exception and predict a typical reaction outcome.