Electron Shell Examples in Chemistry

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

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

Concept Recap

A discrete energy level surrounding the atomic nucleus where electrons reside, with each shell (n = 1, 2, 3, ...) holding a maximum of 2n^2 electrons. Lower shells have less energy and fill first.

Electrons live in 'floors' around the nucleus. Lower floors fill first.

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: Electrons fill lower energy shells before higher ones — this is the basis of the Aufbau principle.

Common stuck point: Electrons don't orbit like planets—they exist in probability clouds.

Sense of Study hint: When determining electron shells for an atom, start filling from the lowest energy shell. First count the total number of electrons (equals atomic number for neutral atoms). Then fill shell 1 with up to 2 electrons, shell 2 with up to 8, shell 3 with up to 18. Finally, the electrons in the outermost occupied shell are the valence electrons.

Worked Examples

Example 1

easy
How many electrons can each of the first three electron shells hold? Show the maximum capacity for shells n = 1, n = 2, and n = 3.

Solution

  1. 1
    The maximum number of electrons in a shell is given by 2n^2 where n is the shell number.
  2. 2
    Shell 1: 2(1)^2 = 2 electrons. Shell 2: 2(2)^2 = 8 electrons.
  3. 3
    Shell 3: 2(3)^2 = 18 electrons.

Answer

n=1: 2,\quad n=2: 8,\quad n=3: 18
Electron shells are energy levels surrounding the nucleus. Inner shells are lower in energy and fill first. The formula 2n^2 determines the capacity of each shell and explains why the periodic table has rows of different lengths.

Example 2

medium
Draw the electron shell diagram (Bohr model) for a sodium atom (Z = 11). How many electrons are in each shell?

Example 3

medium
Draw the electron shell diagram for sodium (Na, Z=11). How many electrons are in each shell?

Practice Problems

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

Example 1

medium
Determine the electron shell arrangement for chlorine (Z = 17). How many electrons are in the outermost shell, and what does this predict about chlorine's chemical behavior?

Example 2

hard
Compare the electron shell arrangements of neon (Z = 10) and argon (Z = 18). Explain why both are chemically inert despite having different numbers of total electrons.
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Background Knowledge

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

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