Practice Electron Configuration in Chemistry

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

The specific arrangement of electrons in an atom's orbitals, described using subshell notation that indicates the energy level, sublevel type, and number of electrons in each subshell.

Electrons fill energy levels like seats in a theatre — front rows first, then moving back.

Showing a random 20 of 50 problems.

Example 1

medium
Write the full electron configuration of sulfur (Z = 16).

Example 2

challenge
Two species Na+Na^+ and F−F^- are isoelectronic. State their common configuration and the electron count.

Example 3

easy
How many electrons can the n=2 shell hold in total?

Example 4

easy
What is the maximum number of electrons in any single p subshell?

Example 5

medium
Write the electron configuration of S2−S^{2-} (S is Z = 16).

Example 6

medium
How many core electrons does phosphorus (Z = 15) have?

Example 7

challenge
Using configurations, explain why the second ionization energy of sodium (Na+Na^+ to Na2+Na^{2+}) is enormous compared to the first.

Example 8

easy
Using noble-gas shorthand, what core symbol precedes sodium's configuration (Z=11Z=11)?

Example 9

medium
Copper is an exception to standard Aufbau filling. Write its ground-state configuration (Z = 29).

Example 10

medium
Write the configuration of calcium (Z = 20) using the argon core.

Example 11

hard
Write the ground-state electron configuration of silver (Z = 47), an Aufbau exception.

Example 12

medium
Identify the neutral element with configuration 1s22s22p63s23p64s23d104p31s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^3.

Example 13

challenge
Cobalt is [Ar]4s23d7[Ar]4s^2 3d^7. Determine the configuration and number of unpaired d electrons in Co2+Co^{2+}.

Example 14

medium
Write the electron configuration of zinc (Z = 30) and state the number of unpaired electrons.

Example 15

challenge
Explain using configurations why the first ionization energy of nitrogen (2p32p^3) exceeds that of oxygen (2p42p^4).

Example 16

medium
Write the electron configuration of bromine (Z = 35).

Example 17

easy
Write the ground-state electron configuration of hydrogen (Z = 1).

Example 18

easy
Write the electron configuration of lithium (Z = 3).

Example 19

easy
Which subshell fills first, 4s or 3d, by the Aufbau principle?

Example 20

hard
Write the electron configuration of V3+V^{3+} (V is Z = 23, neutral [Ar]4s23d3[Ar]4s^2 3d^3).
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