When an electron occupies an orbital of an atom singly, rather than an electron pair such electron is said to be an unpaired electron. Each atomic orbital of an atom specified by quantum numbers can contain a maximum of two electrons having opposite spins, electron pair.
The numbers of unpaired electrons are determined by the electronic configuration of an atom. The electronic configuration of calcium, [tex]Ca[/tex] is:
[tex]1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}[/tex] or [tex][Ar]4s^{2}[/tex]
Since, from the electronic configuration it is clear that the number of electrons in valence orbital that is [tex]4s[/tex] is 2 that means the electrons are paired up in the valence orbital so, there are no unpaired electrons present in [tex]Ca[/tex].
Hence, the number of unpaired electrons in [tex]Ca[/tex] is 0.
Using the s, p, d, f electronic configuration notion, the number of unpaired electrons in an atom of calcium is ZERO.
The electronic configuration of calcuim can be written thus :
The allocation of electrons is as follows :
Ca = [tex]1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6}4s^{2}[/tex]
The pictorial arrangement of electronic configuration is attached below.
Therefore, calcium has 0 number of unpaired electrons.
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