Octet Rule Chemistry Example 4

Follow the full solution, then compare it with the other examples linked below.

hard

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

1
Exception 1 — Incomplete octet: boron in $\text{BF}_3$ has only 6 electrons around it (3 bonds × 2 electrons). Boron is stable with fewer than 8 electrons.
2
Exception 2 — Expanded octet: phosphorus in $\text{PCl}_5$ has 10 electrons around it (5 bonds × 2 electrons). Elements in period 3 and beyond can use $d$ orbitals to accommodate more than 8 electrons.
3
A third exception is odd-electron molecules like NO, which has an unpaired electron and cannot satisfy the octet rule for all atoms.

Answer

\text{Incomplete: BF}_3\text{ (6e}^-\text{). Expanded: PCl}_5\text{ (10e}^-\text{).}

The octet rule is a useful guideline but has important exceptions. Elements with

d

orbitals available (period 3+) can exceed the octet, while some elements like boron and beryllium are stable with fewer than 8 electrons.

About Octet Rule

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.

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

Use the octet rule to explain why sodium forms [formula] and chlorine forms [formula] when they reac

Use the octet rule to explain why oxygen forms two covalent bonds in a water molecule ([formula]).