Question

Which of the following species are hypervalent:
1.$Cl{O_4}^ - \;$
2.$B{F_3}$
3.$S{O_4}^{2 - }$
4.$C{O_3}^{2 - }$
A.1, 2, 3
B.1, 3
C.3, 4
D.1, 2

Answer 1

To answer this question, you should recall the concept of the octet rule. A hypervalent molecule is a molecule that contains one or more main group elements formally bearing more than eight electrons in their valence shells. We shall calculate the number of electrons from the total number of bonds it forms in the molecule.

Complete step by step solution:
The octet rule dictates that atoms are most stable when their valence shells are filled with eight electrons. We know that octet is often made up of its original electrons and a few electrons which are shared. Thus, an atom continues to make bonds until an octet of electrons is formed. When atoms have more than eight electrons, they react with other atoms or ions to make more stable compounds. The d or f electrons aren't considered within the octet rule. Only the s and p electrons are involved within the octet rule, making it useful for the representative elements. This is because the rule only involves s and p electrons, where the octet corresponds to an electron configuration ending with ${{\text{s}}^{\text{2}}}{{\text{p}}^{\text{6}}}$. These elements tend to form bonds to obtain stable octet configurations.
$Cl{O_4}^ -$ is hypervalent as $Cl$ contains more than 8 electrons.
$B{F_3}$ is hypovalent as boron contains 6 electrons.
$S{O_4}^{2 - }$​ is also hypervalent as $S$ contains more than 8 electrons.
$C{O_3}^{2 - }$ has a complete octet of 8 electrons.

Therefore, we can conclude that the correct answer to this question is option B.

Note:
Since, 1p subshells do not exist, some elements find stability in ${\text{1}}{{\text{s}}^{\text{2}}}$ configurations. However, on the other hand, some elements are capable of forming hypervalent molecules. Some elements that disobey the octet rule include: Hydrogen, Lithium, Phosphorus and Sulfur.