Electron Configurations and Magnetic Properties of Ions

We can deduce the electron configuration of a main-group monoatomic ion from the electron configuration of the neutral atom and the charge of the ion. For anions, we add the number of electrons indicated by the magnitude of the charge of the anion. For example, the electron configuration of fluorine (F) is s 2s 2p and that of the fluoride ion 

In other words, for transition metal cations, the order in which electrons are removed upon ionization is not the reverse of the filling order. During filling, the 4s orbital normally fills before the 3d orbital. When a fourth period transition metal ionizes, however, it normally loses its 4s electrons before its 3d electrons. Why this unexpected behavior The full answer to this question is beyond our scope, but the following two factors contribute to this phenomenon. 

The bottom-line experimental observation is that an ns°(n - l)d configuration is lower in energy than an ns (n — V)d configuration for transition metal ions. Therefore, we remove the ns electrons before the (n - )d electrons when writing electron configurations for transition metal ions. 

The magnetic properties of transition metal ions support these assignments. Recall from Section 8.3 that an unpaired electron generates a magnetic field due to its spin. Consequently, an atom or ion that contains unpaired electrons is attracted to an external magnetic field, and we say that the atom or ion is paramagnetic. For example, consider the electron configuration of silver  

Silver s unpaired 5s electron causes silver to be paramagnetic, hi fact, an early demonstration of electron spin—called the Stem-Gerlach experiment—involved the interaction of a beam of silver atoms with a magnetic field. An atom or ion in which aU electrons are paired is not 

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