ATOMIC STRUCTURE

3.4 - Electron Configurations of Atoms

3.4.2 - Electron Configuration Notations

There is a way to represent precisely the electron arrangement in atoms. Let's take a look at the simplest atom, hydrogen.

A hydrogen atom has 1 electron. That electron will occupy the lowest principal energy level, n = 1, and the only sublevel, s. We denote the electron configuration of hydrogen as

Mouseover the image for a description of the symbols.

Similarly,

• Helium has 2 electrons; the 2 electrons both occupy the s sublevel in principal energy level 1.
  • Helium's electron configuration is 1s²
• Lithium has 3 electrons; 2 of the 3 electrons occupy the s sublevel in principal energy level 1. The 3rd electron must go in the next available sublevel, 2s.
  • Lithium's electron configuration is 1s² 2s¹
• Beryllium has 4 electrons; 2 of the 3 electrons occupy the s sublevel in principal energy level 1. The 3rd and 4th electrons must go in the next available sublevel, 2s.
  • Beryllium's electron configuration is 1s² 2s²

   

As an exercise, write the electron configuration for the first 20 elements on the periodic table. Then click to check your answers.

(section 3.4.3)

Section 4.8
Arrangement of Electrons in Sublevels ..p91

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