Question #f2b1a

1 Answer
Nov 18, 2016

Answer:

It's an atom that can have different valencies.

Explanation:

Some atoms can have multiple valencies.
Copper is usually #Cu^(2+)#, but #Cu^+# also exists.
Iron can be #Fe^(2+)# or #Fe^(3+)#

Chlorine is even 'worse':
It has valencies #-1,+1,+3,+5,+7# in ions like:
chloride (#Cl^-#), hypochlorite (#ClO^-#), chlorite (#ClO_2^-#), chlorate (#ClO_3^-#), and perchlorate (#ClO_4^-#).

The above are just examples; there are many more.
In the more elaborate versions of the Periodic System the possible valencies are given.