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Odd-electron molecules, also known as radicals, are species with unpaired electrons in their valence shell. These molecules have an odd number of valence electrons, which makes it difficult for them to form stable electron configurations with a complete octet. Some well-known examples of radicals include nitric oxide (NO) and methyl radical (CH3).

To understand the behavior of odd-electron molecules, we will examine the electronic configurations of the examples mentioned in step 1. Nitric oxide (NO): - Nitrogen has 5 valence electrons, and oxygen has 6 valence electrons. - In the NO molecule, nitrogen forms a double bond with oxygen, sharing 4 electrons in total. As per the bond formation, nitrogen has 7 electrons in its valence shell (5 original + 2 from the double bond), and oxygen has 7 electrons in its valence shell (6 original + 1 from the double bond). - Both nitrogen and oxygen have unpaired electrons, making NO an odd-electron molecule. The octet rule is not satisfied, as both nitrogen and oxygen have 7 valence electrons in their outer shells. Methyl radical (CH3): - Carbon has 4 valence electrons, and hydrogen has 1 valence electron. - In the CH3 radical, carbon shares its 3 electrons with 3 hydrogen atoms, each contributing 1 electron. - Carbon has 7 electrons (4 original + 3 from the bond formation), while each hydrogen atom has 2 electrons in their outer shells. Carbon, being the central atom, does not fulfill the octet rule due to having 7 valence electrons instead of 8, making CH3 an exception to the octet rule.

It is evident from the examples of nitric oxide (NO) and methyl radical (CH3) that odd-electron molecules have unpaired electrons. These molecules cannot achieve a complete octet in their valence shells. Hence, all odd-electron molecules are exceptions to the octet rule.