Electron Configuration — Drills · Grade 11 Science

Chapter: Atoms, Electrons & Periodicity

What these drills covers

By the end of Electron Configuration you should be able to:

6 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: energy level (n), sublevel, orbital, electron configuration, Aufbau principle, Pauli exclusion principle, Hund's rule, valence electrons.

Problem 1

How many orbitals are in a p sublevel?
  1. 3
  2. 5
  3. 7
  4. 1
Answer and explanation

3

A p sublevel has 3 orbitals, holding up to 3 × 2 = 6 electrons.

Problem 2

Using 2n², what is the maximum number of electrons the n = 1 energy level can hold?
Answer and explanation

2

2n² = 2 × 1² = 2 electrons.

Problem 3

Which is the correct ground-state electron configuration of neon (Z = 10)?
  1. 1 s² 2 s² 2p⁶ 3 s²
  2. 1 s² 2 s² 2p⁶
  3. 1 s² 2 s² 2p⁴
  4. 1 s² 2 s² 2p⁸
Answer and explanation

1 s² 2 s² 2p⁶

Ten electrons fill 1 s² 2 s² 2p⁶ (2 + 2 + 6 = 10), a full second shell.

Problem 4

Sulfur's configuration is 1 s² 2 s² 2p⁶ 3 s² 3p⁴. How many valence electrons does it have?
Answer and explanation

6

Valence electrons are those in the highest level (n = 3): 3 s² 3p⁴ = 6.

Problem 5

Briefly state, in your own words, what the Aufbau principle, the Pauli exclusion principle, and Hund's rule each say.
Answer and explanation

Aufbau: fill the lowest-energy sublevels first. Pauli: no orbital can hold more than two electrons, and they must have opposite spins. Hund: within a sublevel, electrons spread out one per orbital before any orbital gets a second electron.

Problem 6

What is the noble-gas shorthand electron configuration for iron (Z = 26)?
  1. [Ne] 4 s² 3d⁶
  2. [Ar] 4 s² 4d⁶
  3. [Ar] 4 s² 3d⁶
  4. [Ar] 3d⁸
Answer and explanation

[Ar] 4 s² 3d⁶

After [Ar] (18 electrons), the remaining 8 fill 4 s before 3d: 4 s² 3d⁶, giving [Ar] 4 s² 3d⁶.

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