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Lesson · Grade 11 · Chemistry

Writing Electron Configurations

  • Grade 11
  • Chemistry
  • 2 min 19 s
  • British Columbia
  • BC11-SC-02

Using sulfur's 16 electrons, the video introduces orbitals, the Pauli exclusion principle, subshells and the diagonal chart of the filling order. It then writes 1s² 2s² 2p⁶ 3s² 3p⁴ with orbital boxes, applies Hund's rule to 3p, shortens the result to [Ne] 3s² 3p⁴, and uses potassium ([Ar] 4s¹) to show that 4s fills before 3d.

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In one sentence

The question this lesson answers

Sulfur has 16 electrons. How do we write its electron configuration: where each one goes?

In the quantum mechanical model, electrons occupy orbitals: regions where they are likely to be found.

Transcript

What the lesson says

Sulfur has 16 electrons. How do we write its electron configuration: where each one goes?

In the quantum mechanical model, electrons occupy orbitals: regions where they are likely to be found.

Pauli exclusion principle: an orbital holds at most two electrons, with opposite spins, up and down.

Orbitals form subshells: an s subshell has one orbital, p has three, and d has five.

So s holds 2 electrons, p holds 6, and d holds 10.

Each chart row is a shell, or energy level: 3p is the p subshell of shell 3.

Lowest energy subshells fill first, following the arrows: 1s, 2s, 2p, 3s, 3p, 4s, then 3d.

Write each subshell with its electron count raised: 1s takes 2, 2s takes 2, 2p takes 6.

Then 3s takes 2, and the last 4 go into 3p.

Hund's rule: electrons enter empty orbitals one at a time, with the same spin, before pairing.

The fourth 3p electron must pair up: one pair and two unpaired electrons.

Check: 2 plus 2 plus 6 plus 2 plus 4 makes 16. That is sulfur's electron configuration.

The first 10 electrons match neon, so shorthand writes them as Ne in brackets, then 3s and 3p.

Careful: 3d does not come straight after 3p. On the chart, 4s comes first.

Potassium has 19 electrons: 18 like argon, then the 19th goes into 4s, not 3d.

To sum up: chart order, two opposite spins per orbital, and spread out before pairing.

Curriculum

Where this fits

British Columbia, Grade 11

Chemistry 11, Atoms and electrons: quantum mechanical model and electron configurationBC11-SC-02

Previous: Electrons in Orbitals: The Quantum Mechanical ModelNext: Valence electrons: the outer electrons that bond

The outcomes and strands follow the British Columbia curriculum.

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