Question

In which species does the central atom obey the octet rule?
A. $Xe{F_4}$
B. $S{F_4}$
C. $Si{F_4}$
D. $Cl{F_4}$

Answer 1

The octet rule states that atoms are most stable only when there are eight electrons filled in their valence shells. Some elements that disobey the octet rule include, Hydrogen, Lithium, Phosphorus and Sulphur. An ion, atom, or a molecule that contain an unpaired valence electron, i.e., a free radical, so these species do not obey the octet rule.

Complete step by step answer:
In $Xe{F_4}$, there are not 8 electrons in outermost orbit that are completely filled, the Xe atom has 12 valence electrons, i.e., it does not obey octet rule. $Xe{F_4}$ does not follow the octet rule. Xeon starts with an octet sharing electrons with Fluorine only disrupts the octet it started with.
In $S{F_4}$, the central atom does not obey octet rule. Around the sulphur atom, there is a lone pair that's why the molecule is polar. But the odd number of lone pair methods works. The molecule is polar because bond dipoles do not cancel.
In $Si{F_4}$, it has a total of 31 valence electrons and when these electrons are distributed throughout the atoms to make bonds and place lone pairs, there are no nonbonding pairs on the central Si atom. The central atom here, Si, obeys the octet rule because it is surrounded by 8 electrons i.e., 4 bonding pairs. Also, all of the F atoms also conform to the octet rule as each F atom is surrounded by 8 valence electrons i.e., 3 nonbonding pairs and 1 bonding pair.
In $Cl{F_4}$, the central atom does not obey octet rule as it has an unpaired valence electron, i.e., a free radical, so these species do not obey the octet rule.

Therefore, the correct answer is option (C).

Note: An atom follows an octet rule if the atom other than the hydrogen tends to form bonds until it is surrounded by eight valence electrons or until it has a similar electronic configuration as the noble gases. Here, Hydrogen (H) n is an exception as it conforms to the duet rule, in which it should be surrounded by only two electrons to be able to remain stable. And aside from hydrogen, there are also atoms which do not strictly follow the octet rule such as those with expanded octet, incomplete octet, and odd-electron molecules.