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5.19: Noble Gas Configuration

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  • You had a great meal, but cannot put another bite in your mouth because there is no place for it to go. The noble gases have the same problem - there is no room for any more electrons in their outer shells. They are completely full and cannot handle any more.

    Noble Gas Configuration

    Sodium, element number eleven, is the first element in the third period of the periodic table. Its electron configuration is \(1s^2 2s^2 2p^6 3s^1\). The first ten electrons of the sodium atom are the inner-shell electrons and the configuration of just those ten electrons is exactly the same as the configuration of the element neon \(\left( Z=10 \right)\). This provides the basis for a shorthand notation for electron configurations called the noble gas configuration. The elements that are found in the last column of the periodic table are an important group of elements that are called the noble gases. They are helium, neon, argon, krypton, xenon, and radon. A noble gas configuration of an atom consists of the elemental symbol of the last noble gas prior to that atom, followed by the configuration of the remaining electrons. So for sodium, we make the substitution of \(\left[ \ce{Ne} \right]\) for the \(1s^2 2s^2 2p^6\) part of the configuration. Sodium's noble gas configuration becomes \(\left[ \ce{Ne} \right] 3s^1\). Table \(\PageIndex{1}\) shows the noble gas configurations of the third period elements.

    Table \(\PageIndex{1}\): Electron Configurations of Third-Period Elements
    Element Name Symbol Atomic Number Noble Gas Electron Configuration
    Sodium \(\ce{Na}\) 11 \(\left[ \ce{Ne} \right] 3s^1\)
    Magnesium \(\ce{Mg}\) 12 \(\left[ \ce{Ne} \right] 3s^2\)
    Aluminum \(\ce{Al}\) 13 \(\left[ \ce{Ne} \right] 3s^2 3p^1\)
    Silicon \(\ce{Si}\) 14 \(\left[ \ce{Ne} \right] 3s^2 3p^2\)
    Phosphorus \(\ce{P}\) 15 \(\left[ \ce{Ne} \right] 3s^2 3p^3\)
    Sulfur \(\ce{S}\) 16 \(\left[ \ce{Ne} \right] 3s^2 3p^4\)
    Chlorine \(\ce{Cl}\) 17 \(\left[ \ce{Ne} \right] 3s^2 3p^5\)
    Argon \(\ce{Ar}\) 18 \(\left[ \ce{Ne} \right] 3s^2 3p^6\)

    Again, the number of valence electrons increases from one to eight across the third period.

    The fourth and subsequent periods follow the same pattern except for using a different noble gas. Potassium has nineteen electrons, one more than the noble gas argon, so its configuration could be written as \(\left[ \ce{Ar} \right] 4s^1\). In a similar fashion, strontium has two more electrons than the noble gas krypton, which would allow us to write its electron configuration as \(\left[ \ce{Kr} \right] 5s^2\). All the elements can be represented in this fashion.


    • The noble gas configuration system allows some shortening of the total electron configuration by using the symbol for the noble gas of the previous period as part of the pattern of electrons.


    • CK-12 Foundation by Sharon Bewick, Richard Parsons, Therese Forsythe, Shonna Robinson, and Jean Dupon.