Which of the following shows maximum number of different oxidation states in its compounds? Why?
A. Eu B. La C. Gd D. Am
Ans. D (Am) is the correct option.
Am belongs to Actinides series in which electron are filled in 5f orbitals. And due to less energy difference between 5d, 6d and 7s orbitals, electrons are easily removed from these orbitals showing the variable oxidation state. Thus Am shows maximum number of oxidation state.
While other elements belongs to lanthanides series in which electron are filled in 4f orbitals. Since energy difference between 4f, 5d, and 6s orbitals is very large, so electron cannot be removed from inner orbitals and hence cannot show variable oxidation states.
Am belongs to Actinides series in which electron are filled in 5f orbitals. And due to less energy difference between 5d, 6d and 7s orbitals, electrons are easily removed from these orbitals showing the variable oxidation state. Thus Am shows maximum number of oxidation state.
While other elements belongs to lanthanides series in which electron are filled in 4f orbitals. Since energy difference between 4f, 5d, and 6s orbitals is very large, so electron cannot be removed from inner orbitals and hence cannot show variable oxidation states.