Question

Electron configurations of transition metal ions

Zinc is an essential mineral of great biological and health importance. In fact, it is the second most abundant transition metal after iron in our body. Most exists as Zn2+ ion in active site of enzymes, and they (more than 300) perform an array of functions.

a. What is the electronic configuration of the Zn atom.

b. Here comes the irritating part in chemistry. Although the 3d orbitals are placed higher in energy than the 4s orbital, when it comes to losing electrons to from the Zn2+ ions, the 4s electrons go first. If so, what is the electronic configuration of Zn2+ ion?

c. Using these rules, deduce the electronic configuration of Co2+ d. Unpaired electrons generate a small magnetic field and are responsible for the magnetic properties of materials. If an atom (or molecule) has no unpaired electrons, it is called diamagnetic. On the other hand, if it does have unpaired electrons, it is called paramagnetic. Is Zn2+ diamagnetic or paramagnetic? How about Co2+?

Answer 1

a.

Zn (Zinc) has atomic number 30. Hence, a neutral Zn atom has 30 electrons with electronic configuration as follows:

Zn: 1s2 2s 2p 3s 3p 4s2 3d

Or it can be written as in noble gas core notation.

b.

$Zn^{2+}$ ion is formed by Zn losing two of its outermost electron. Since 4s orbital is the outermost orbital even though it is lower energy than 3d orbital, the electrons are lost from 4s orbital first.

Hence, the electronic configuration of $Zn^{2+}$ is

Or in noble gas core notation

c.

Co(Cobalt) has atomic number 27.

Hence, the electronic configuration of Cobalt with 27 electrons is

Now, to form the $Co^{2+}$ ion we need to remove two electrons from 4s orbital.

Hence, the electronic configuration of Co2+ ion is

or in Noble gas core notation

d.

Outermost orbital of Zn2+ is the 3d orbital with 10 electrons.

$3d^{10}$

$\uparrow \downarrow$

$\uparrow \downarrow$

$\uparrow \downarrow$

$\uparrow \downarrow$

$\uparrow \downarrow$

Hence, all the electrons in Zn2+ ion are paired. Hence, it is diamagnetic.

Outermost orbital of Co2+ is the 3d orbital with 7 electrons which are filled as follows:

$3d^{10}$

$\uparrow \downarrow$

$\uparrow \downarrow$

$\uparrow$

$\uparrow$

$\uparrow$

Hence, there are three unpaired electrons in $Co^{2+}$ . Hence, it must be paramagnetic.