Question

Define octet rule. Write its significance and limitations.

Answer 1

The octet rule is a chemical rule of thumb that reflects observation that atoms of main-group elements tend to combine in such a way that each atom has eight electrons in its valence shell, giving it the same electron configuration as a noble gas.

Significance: The octet rule successfully explains the formation of chemical bonds depending upon the nature of the element. It is used to determine stability in atoms. The octet rule helps to figure out how atoms will bond with one another.

Limitations: One limitation of the octet rule is that it cannot be applied to the nonmetals after silicon in the Periodic Table. These elements can “expand their octet” and have more than eight valence electrons around the central atom. Molecules with an odd number of electrons such as NO and NO2 cannot satisfy the octet rule.

Answer 2

Octet Rule

Q1. What is an octet rule?

Ans: Atoms of elements combine with each other in order to complete their respective octets so as to acquire the stable electronic configuration. Each atom either gain or loss electrons to complete it's outermost shell. As a result, molecules are formed. Octet is the tendency of an atom to acquire outermost shell of it's eight valence electrons.

Q2. Significance of octet rule?

Ans: It helps to explain why different atoms combine with each other to form ionic compounds or covalent compounds.

Q3. Limitations of octet rule?

Ans: 1) According to octet rule, atoms take part in chemical reaction to achieve the configuration of nearest noble gas elements. However, some of noble gases like Xenon and Krypton have formed compounds with fluorine and oxygen like XeF₂ , KrF₂ , XeOF₂ etc.

2) This rule doesn't account for the shape of molecules.

3) It doesn't explain the relative stability of the molecules being totally silent about the energy of a molecule.

Q4. Some exceptions of octet rule.

Ans: Some molecules have less than eight electrons in a lewis structure. BF₃ is an example. These are known as electron-deficient compounds. SF₆ is an example. Some molecules have an odd number of electrons when summing up the total number of electrons. These don't obey the octet rule. NO [Nitrogen Monoxide] is an example.

Q5. Define Free Radical.

Ans: Free radical is an ion, atom or a molecule containing an unpaired valence electron.

Q6. Due to the presence of which orbital, the transition elements don't obey the octet rule.

Ans: f-orbital