Use the periodic table to predict the characteristic valence-electron configuration of the halogens.

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jerichorayel | College Teacher | (Level 2) Senior Educator

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First, we have to locate the halogens in the periodic table. It is located at the group 17 (second from the right).

Valence electrons are the outermost electrons in a particular atom which is generally the electrons that participate in certain reactions. Halogens (Fluorine, Chlorine, Bromine, Iodine, and Astatine) have valence electrons of seven.

They belong to the p-group elements which mean that their valence electrons are the electrons present in the last s and p orbitals in the electronic configuration. Let us try to write down the electronic configuration of the halogens:

(Consider the bolded configurations)

F = 1s^2 2s^2 2p^5 

Cl = 1s^2 2s^2 2p^6 3s^2 3p^5

Br = 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^5

I = 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^10 5p^5

At = 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^10 5p^6 6s^2 4f^14 5d^10 6p^5

All of them have the same valence electron configuration of s^2 p^5 or seven valence electrons. 

Sources:

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