Electron Shell Chemistry Example 3

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Example 3

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

Solution

  1. 1
    Sodium has atomic number Z=11Z = 11, so a neutral sodium atom has 11 electrons. Shells are filled from the innermost outward.
  2. 2
    Shell 1 (K shell) holds a maximum of 2n2=2(1)2=22n^2 = 2(1)^2 = 2 electrons. Fill it: **2 electrons**. Remaining: 11−2=911 - 2 = 9.
  3. 3
    Shell 2 (L shell) holds a maximum of 2(2)2=82(2)^2 = 8 electrons. Fill it: **8 electrons**. Remaining: 9−8=19 - 8 = 1. Shell 3 (M shell): **1 electron**. The configuration is 2, 8, 12,\, 8,\, 1.

Answer

Na electron shell arrangement: Shell 1 = 2, Shell 2 = 8, Shell 3 = 1 (written 2, 8, 12,\, 8,\, 1).
The electron shell model shows that sodium has one electron in its outermost shell. This single valence electron is easily lost, which is why sodium forms Na+\text{Na}^+ ions and is a highly reactive alkali metal.

About Electron Shell

A discrete energy level surrounding the atomic nucleus where electrons reside, with each shell (n=1,2,3,...n = 1, 2, 3, ...) holding a maximum of 2n22n^2.

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