Question

Which of the following compounds does not follow the octet rule for electron distribution
A.\[PC{{l}_{5}}\]
B. \[PC{{l}_{3}}\]
C.\[{{H}_{2}}O\]
D.\[P{{H}_{3}}\]

Answer 1

Hint: According to the octet rule, atoms shape into compounds in such a way that they give them eight valence electrons.
The octet rule is satisfied by many compounds but there are exceptions like helium which only has two valence electrons.

Complete step by step solution:According to the octet rule, atoms shape into compounds in such a way that they give them eight valence electrons like the inert gas configuration.
Helium is an exception.
Lithium which is an alkali metal also does not obey the octet rule.
It tends to remove one electron to have the helium configuration.
Octet rule can be obeyed by sharing the valence electrons with other atoms or by giving and taking the valence electrons from one atom to another.
Here in this question, we are given compounds and we have to find out which does not follow the octet rule.
A. \[PC{{l}_{5}}\]
In PCl5, covalent bonding takes place.
P has five electrons in its outermost shell.
Each Cl atom shares one electron with the P atom. So, the total contribution from all the Cl atoms is 5.
The total electrons are 10.
So, it does not follow the octet rule.
So, A is correct.
B. \[PC{{l}_{3}}\]
P has 5 electrons and each Cl atom shares one electron as well.
So, the total electrons are 8.
So, B is incorrect.

C. \[{{H}_{2}}O\]
Oxygen has six electrons in its outermost shell.
Each H atom shares one electron with the I atom. So, the total contribution from two H atoms is 2.
The total electrons are 8.
So, it follows the octet rule.
So, C is incorrect.

D. \[P{{H}_{3}}\]
P has five electrons in its outermost shell.
Each H atom shares one electron with the I atom. So, the total contribution from three H atoms is 3.
The total electrons are 8.
So, it follows the octet rule.
So, D is incorrect.

So, option A is correct.

Note: Noble gases do not react with other elements because of their electron configurations.
The noble gas neon has the electron configuration of\[1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}\].
The outer shell is filled and it cannot bring any more electrons into the valence shell.
The other noble gases maintain the same outer-shell electron configuration but have diverse inner-shell electron numbers.
American chemist Gilbert Lewis used this theory and made the octet rule.