Hey guys,
The answer keys says Sr++ is smaller than S--, why is that? Sr++ has a Kr configuration, while S-- has a Ar right? Then shouldn't Kr has 1 more layer of electrons than Ar?
Thanks again for the help!
This is a great question.....I love your enthusiasm for learning ! When a neutral atom becomes an ion, we do indeed expect a change in the size. If an anion forms, the size (or radius) increases, since the nuclear charge remains the same but the repulsion resulting from the additional electrons allows the electron cloud to increase its domain. Removal of an electron will reduce electron-electron repulsion but the nuclear charge remains the same, thus the electron cloud gets smaller, thus the cation is smaller than the atom. For ions derived from DIFFERENT GROUPS,,,,,, a size comparison is ONLY meaningful if the ions are ISOELECTRONIC. From the literature values Sr cation is 113pm, and S anion is 184 !!!!! Clearly these two are not isoelectronic,,,Good Call......thus we need to make a judgment call. Losing 2 electrons Drastically shrinks the cloud,,,,while adding 2 Drastically enlarges the clouds, Yes,,,,there are exceptions.....but for the DAT....... it is unlikely you will see them without further info. As a general rule......Do not bet against an Ion when it comes to size,,,,, The size of Te anion is 221 pm.....and Iodide anion is 216 !!!!! Al cation is a mere 50 !!!!!!! Bottom Line......Negative ions are Big,,,,,,Positive ions are small !!!!!!
Hope this helps .
