Question

According to Hund's rule, the lowest (ground) state of the silicon atom ___.a. has 2 unpaired electrons b. has four different orbitals less than fully occupied c. has three sets of paired valence electrons d. has four unpaired electrons

Answer 1

Answer: Option (a) is the correct answer.

Explanation:

According to Hund's rule, each orbital of a sub-shell is occupied by a single electron first even before it is occupied by two electrons in the same orbital. And, all the electrons in singly occupied orbitals tend to have same spin.

Atomic number of silicon is 14 and its electronic configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{2}$. This means that there are two electrons present in its valence shell which have same spin.

Thus, we can conclude that according to Hund's rule, the lowest (ground) state of the silicon atom has 2 unpaired electrons.

Answer 2

There are  2 unpaired electrons in the lowest energy (ground state) of the silicon atom.

The ground state electronic configuration of silicon is  1s2 2s2 2p6 3s2 3p2. Let us recall that the ground state is the lowest energy state of an atom. Hund's rule states that, electrons occur singly first before pairing takes place.

The electrons in the 3p orbitals will be filled into any two of the degenerate 3px, 3py and 3pz orbitals according to Hund's rule. Hence, there are  2 unpaired electrons in the lowest energy (ground state) of the silicon atom.

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