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Why does K+ have 0 valence electrons?

up vote 14 down vote favorite

If we take a K atom and take away an electron why does it now have 0 valence electrons as it states in my General Chemistry textbook? I would think that if we do this, it would have the same exact electron configuration as Ar, which has 8 valence electrons? What's going on here?

2 Answers

up vote 4 down vote accept

You are correct in that it has 8 valence electrons, not 0. If we look at the electron configuration of potassium (K), we see that it has one electron: [Ar]4s1. Obviously, removing that electron gives us [Ar] (same configuration as K1+), which is a noble gas and has 8 electrons.

up vote 3 down vote

What you say is correct. The [Ar] configuration we are left with does have 8 valence electrons. But I think it is just semantics. Elemental potassium has an [Ar] 4s1 electron configuration. One would say it has one valence electron. If we take that one valence electron away, it makes sense to say that it now has zero valence electrons because "1 - 1 = 0".


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Why does K+ have 0 valence electrons?

up vote 14 down vote

If we take a K atom and take away an electron why does it now have 0 valence electrons as it states in my General Chemistry textbook? I would think that if we do this, it would have the same exact electron configuration as Ar, which has 8 valence electrons? What's going on here?


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up vote 9 down vote

You are correct in that it has 8 valence electrons, not 0. If we look at the electron configuration of potassium (K), we see that it has one electron: [Ar]4s1. Obviously, removing that electron gives us [Ar] (same configuration as K1+), which is a noble gas and has 8 electrons.

edit

The definition of a valence electron is an electron involved in bonding. As the electrons in the 3rd shell of K are not involved in bonding, it does not make sense to call them valence electrons. K forms metallic bonds with its one 4s electron, and ionic bonds by giving it up to form K+. On the other hand, argon does use the electrons in the 3rd shell to form (covalent/dative) bonds, in the very limited number of compounds it forms. This (3) is the longest list I could find endmemo.com/chem/common/argon.php - steveverrill Sep 29 at 14:00

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