Recall that ionic radius is the size of an ion. The trend for ionic radius is as follows: it increases from right to left and down a period in the periodic table. Ionic radius also increases with increasing number of electrons.
Co3+:
Co: atomic number = 27
neutral Co = 27 electrons
Co3+ = 27 e- - 3 e-
Co3+ = 24 e-
Fe3+:
Fe: atomic number = 26
neutral Fe = 26 electrons
Fe3+ = 26 e- - 3 e-
Fe3+ = 23 e-
Fe2+
Fe: atomic number = 26
neutral Fe = 26 electrons
Fe2+ = 26 e- - 2 e-
Fe3+ = 24 e-
Fe3+: → least # of electrons → smallest size
Co3+ and Fe3+ → same number of electrons → isoelectronic
For the following set of atoms and ions, arrange the members in order of decreasing size: Rank items from largest to smallest. To rank items as equivalent, overlap them.
Co3+ , Fe3+, Fe2+
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