On what ground can you say that scandium (Z = 21) is a transition element but zinc (Z = 30) is not?

To determine why scandium (Z = 21) is classified as a transition element while zinc (Z = 30) is not, we need to delve into the definitions and characteristics of transition metals as outlined in the periodic table. Transition metals are typically defined by their ability to form variable oxidation states and to have partially filled d-orbitals in their elemental or common oxidation states.

Understanding Transition Metals

Transition metals are found in the d-block of the periodic table, which includes groups 3 to 12. They are characterized by the presence of d-electrons that can participate in bonding and contribute to various oxidation states. This ability to lose different numbers of electrons leads to a wide range of chemical behaviors and complex ion formations.

Scandium: A Transition Element

Scandium, with an atomic number of 21, has the electron configuration of [Ar] 3d¹ 4s². In its common oxidation state of +3, scandium loses all three of its outer electrons (two from the 4s subshell and one from the 3d subshell). This results in a partially filled d-orbital, which is a key characteristic of transition metals. The presence of this d-electron allows scandium to exhibit typical transition metal properties, such as forming colored compounds and complex ions.

Zinc: Not a Transition Element

On the other hand, zinc has an atomic number of 30 and an electron configuration of [Ar] 3d¹⁰ 4s². In its most common oxidation state of +2, zinc loses the two 4s electrons, leaving the 3d subshell completely filled (3d¹⁰). This filled d-orbital means that zinc does not exhibit the variable oxidation states typical of transition metals. Instead, it behaves more like a main group element, lacking the characteristic properties associated with transition metals, such as the formation of colored compounds or complex ions.

Key Differences Summarized

• Electron Configuration: Scandium has a partially filled d-orbital, while zinc has a fully filled d-orbital.
• Oxidation States: Scandium can exhibit multiple oxidation states (+3 being the most common), whereas zinc primarily exists in a +2 state.
• Chemical Behavior: Scandium shows typical transition metal properties, while zinc behaves more like a main group element.

In summary, the classification of scandium as a transition element and zinc as not a transition element hinges on their electron configurations and the resulting chemical properties. Scandium's ability to form variable oxidation states and its partially filled d-orbitals align with the definition of transition metals, while zinc's filled d-orbital and limited oxidation states do not.