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48 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER
5
Because a new principal energy level always begins with the element immediately following one of the noble gases, it is possible to
simplify electron configurations by using the symbol of the previous
noble gas to denote all of an atom’s inner-level electrons. As a simple example, consider nitrogen’s electron configuration of 1s 2 2s 2 2p 3 .
Helium, the preceding noble gas, has the configuration 1s 2 . Thus,
the symbol [He] can be substituted into nitrogen’s configuration to
give [He]2s 1 2p 3 . This form of an electron configuration is called
noble-gas notation.
Example Problem 5-1
Writing Electron Configurations Using Noble-Gas Notation
Use noble-gas notation to write the electron configuration for a neutral atom of silicon.
To begin, find silicon on the periodic table and locate the preceding
noble gas. Silicon (Si) is atomic number 14, and the preceding noble
gas is neon (Ne), atomic number 10.
Start the electron configuration by writing the symbol [Ne]. Note
that [Ne] replaces 1s 2 2s 2 2p 6 , which is neon’s electron configuration.
Next, note that silicon has four more electrons than neon. According
to the energy sublevel diagram, two of these electrons will fill the 3s
sublevel, and the remaining two electrons will occupy orbitals in the
3p sublevel.
By combining this information, you can write the following electron
configuration for silicon.
Si [Ne]3s 2 3p 2