Electron Configuration Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Electron Configuration.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept 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.

Read the full concept explanation →

How to Use These Examples

Read the first worked example with the solution open so the structure is clear.
Try the practice problems before revealing each solution.
Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Electron Configuration starts by naming the element, charge, and relevant protons, neutrons, or electrons.

Common stuck point: Students often know a formula related to electron configuration but skip the recognition step: Am I using particle counts, nuclear charge, mass number, electron arrangement, or isotope notation to describe an atom or ion? That leads to a correct-looking substitution attached to the wrong chemical model.

Sense of Study hint: Ask: Am I using particle counts, nuclear charge, mass number, electron arrangement, or isotope notation to describe an atom or ion?

Worked Examples

Example 1

medium

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

Answer

[Ar]4s^1 3d^{10}

First step

Naive Aufbau predicts

[Ar]4s^2 3d^9

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Example 2

medium

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

Example 3

hard

How many unpaired electrons does manganese (Z = 25,

[Ar]4s^2 3d^5

) have?

Example 4

hard

Predict whether

Cu^{2+}

is paramagnetic or diamagnetic. Cu is

[Ar]4s^1 3d^{10}

Example 5

challenge

Identify the element whose neutral atom has 4 unpaired electrons and configuration ending in

3d^x

. Specify its Z.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy

Write the ground-state electron configuration of helium (Z = 2).

Helium atom — fill the one shell

Example 2

easy

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

Example 3

easy

Write the electron configuration of carbon (Z = 6).

Carbon atom — write the configuration

Example 4

easy

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

Example 5

easy

How many electrons does a neutral neon atom (Z = 10) have in its configuration?

Neon atom — how many electrons total?

Example 6

easy

Write the electron configuration of neon (Z = 10).

Example 7

easy

How many unpaired electrons are in nitrogen's 2p subshell (

2p^3

) by Hund's rule?

Nitrogen — how many unpaired electrons in the valence shell?

Example 8

easy

Using noble-gas shorthand, what core symbol precedes sodium's configuration (

Z=11

Example 9

medium

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

Sulfur atom (Z = 16) — write the full configuration

Example 10

medium

Write the electron configuration of the iron(III) ion

Fe^{3+}

(Fe is

[Ar]4s^2 3d^6

Example 11

medium

Write the configuration of the oxide ion

O^{2-}

(O is

1s^2 2s^2 2p^4

Oxide ion O²⁻ — write the electron configuration

Example 12

medium

Chromium is an exception: instead of

[Ar]4s^2 3d^4

, what is its actual configuration?

Example 13

medium

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

Phosphorus (Z = 15) — how many core electrons?

Example 14

medium

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

Calcium atom (Z = 20) — write using the argon core

Example 15

medium

How many valence electrons does chlorine (

[Ne]3s^2 3p^5

) have?

Chlorine — how many valence electrons?

Example 16

medium

Write the electron configuration of magnesium (Z = 12).

Magnesium atom (Z = 12) — write the full configuration

Example 17

medium

Identify the neutral element with configuration

1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^3

Example 18

challenge

Cobalt is

[Ar]4s^2 3d^7

. Determine the configuration and number of unpaired d electrons in

Co^{2+}

Example 19

challenge

Two species

Na^+

and

F^-

are isoelectronic. State their common configuration and the electron count.

Example 20

challenge

Explain using configurations why the first ionization energy of nitrogen (

2p^3

) exceeds that of oxygen (

2p^4

Example 21

easy

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

Example 22

easy

What is the maximum number of electrons in an s subshell?

Example 23

easy

What is the maximum number of electrons in a d subshell?

Example 24

easy

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

Example 25

easy

Write the electron configuration of boron (Z = 5).

Example 26

easy

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

Example 27

medium

Write the electron configuration of argon (Z = 18).

Example 28

medium

Write the noble-gas shorthand configuration of potassium (Z = 19).

Example 29

medium

Write the full electron configuration of titanium (Z = 22).

Example 30

medium

How many unpaired electrons does silicon (Z = 14,

[Ne]3s^2 3p^2

) have in its ground state?

Example 31

medium

Write the electron configuration of

Mg^{2+}

(Mg is Z = 12).

Example 32

medium

Write the electron configuration of

S^{2-}

(S is Z = 16).

Example 33

medium

How many valence electrons does selenium (

[Ar]4s^2 3d^{10} 4p^4

) have?

Example 34

medium

Identify the neutral element with configuration

[Kr]5s^2 4d^{10} 5p^2

Example 35

medium

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

Example 36

medium

In which block of the periodic table is an element ending in

np^3

found?

Example 37

hard

Write the electron configuration of

Fe^{2+}

(Fe is

[Ar]4s^2 3d^6

Example 38

hard

Write the electron configuration of

V^{3+}

(V is Z = 23, neutral

[Ar]4s^2 3d^3

Example 39

hard

Identify the neutral element with the configuration

[Ar]4s^2 3d^{10} 4p^6

Example 40

hard

How many electrons in a sulfur atom (Z = 16) have

\ell = 1

(i.e., are in p orbitals)?

Example 41

hard

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

Example 42

challenge

Using configurations, explain why the second ionization energy of sodium (

Na^+

Na^{2+}

) is enormous compared to the first.

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Related Concepts

Electron Shell Valence Electron Periodic Table Chemical Bond

Background Knowledge

These ideas may be useful before you work through the harder examples.

electron shellvalence electron