Elements and Compounds

Why does ionisation result in a decrease in size for potassium but an increase in chlorine?

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2007-06-01 07:58:03

Ionization of potassium (K) results in a positive ion, K+, which

has the electronic configuration of Ar. The ionization of chlorine

(Cl) results in a negative ion (Cl-), also with the electronic

configuration of Ar. Adding an electron always increases the size

of an atom, and removing one always decreases its size.


Note that both K+ and Cl- have the same number of electrons, but

Cl- is larger than K+, because they are not as tightly held to the

nucleus in Cl- because it has 2 less protons than potassium does.

The size of the electron cloud determines the size of the atom and

with fewer positively charged protons to pull the same number of

electrons in close to the nucleus the electron cloud is larger for

Cl-.


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