D-Block Elements: Transition Elements and Their Characteristics

The relationship between transition elements and d-block elements has long been a subject of discussion, with cases of Scandium (Sc) and Zinc (Zn) providing exceptions. In this article, we delve into the characteristics and definitions of both transition elements and d-block elements, and explore why not all d-block elements are considered transition elements.

Introduction to Transition Elements and D-Block Elements

The term 'transition elements' originally referred to elements in which the inner d-orbital was being filled. This process involves ten elements in each series to complete, such as from Scandium ([Ar] 3d1 4s2) to Zinc ([Ar] 3d10 4s2).

Traditionally, transitional metal chemistry was only seen in groups 4 to 12. However, it is now understood that certain group 3 and 12 elements can also be considered transition elements, as they can form more than one oxidation state, such as Scandium (Sc) and the future element Copernicium (Cn) in group 12.

Characteristics of Transition Elements

A transition metal is one which forms one or more stable ions that have incompletely filled d orbitals. For example, Copper (Cu) can form Cu2 ions with the electronic structure [Ar] 3d9, which is incomplete, making it a transition element.

However, elements like Zinc (Zn) and Cadmium (Cd) do not meet this criterion, as they form fully filled d-orbitals in both their ground and oxidized states. The compounds or ions Zn2 and Cd2 both have a fully filled d-orbital or subshell. This is why Zn, Cd, and Hg are not considered transition metals.

The Classification of D-Block Elements and Transition Elements

All transition elements are d-block elements, but not all d-block elements are transition elements. D-block elements in shells 4 and 5 (like Zn and Cd) do not have partially filled d orbitals in their ground state, thus do not fall into the definition of transition elements. These elements are considered to be in the intermediate state between s-block and d-block elements.

It is important to note that all transition elements are d-block elements, meaning they are from shells 6 or 7 which have an extra 14 count, but not all d-block elements fall into this category.

Examples of Transition and Non-Transition D-Block Elements

Let's take a closer look at Scandium (Sc) and Zinc (Zn) as examples:

Scandium (Sc):

Electronic structure: [Ar] 3d1 4s2 Cation formed: Sc3 loses 3 outer electrons, resulting in [Ar] structure No 3d electrons in Sc3 ion, thus not a transition element

Zinc (Zn):

Electronic structure: [Ar] 3d10 4s2 Ions formed: Zn2 loses the two 4s electrons, resulting in [Ar] 3d10 ion Fully filled d-orbital in Zn2 ion, thus not a transition element

On the other hand, Copper (Cu) is a clear example of a transition element, as it can lose 4s electrons and form Cu2 with an incomplete 3d orbital.

Conclusion

Understanding the distinction between transition elements and d-block elements is crucial in the study of inorganic chemistry. While all transition elements are d-block elements, not all d-block elements are transition elements. This highlights the importance of the criteria for partial d-orbital filling in determining whether an element is a transition metal.

Keywords

d-block elements transition elements zinc copper