Why Is a Silver Atom a Transition Element Despite a Completely Filled d-Orbital?

At first glance, silver (Ag) with an atomic number of 47 might seem like an anomaly within the transition metals group. This is because its electron configuration is typically described with a completely filled 4d subshell and a single 5s electron. However, silver fulfills a crucial criterion that makes it a transition element. In its various oxidation states, silver demonstrates the defining characteristic of transition metals: the participation of d-orbital electrons in chemical reactions.

Defining Characteristics of Transition Metals

The periodic table categorizes elements into groups based on their outer electron configurations. Transition metals are found in the d-block, characterized by partially filled d orbitals in at least one of their oxidation states. This unique feature allows them to engage in chemical reactions in flexible and diverse ways.

The Electron Configuration of Silver

The typical electron configuration of silver is given as:

[Kr] 4d10 5s1

However, in its elemental state, silver has a completely filled 4d subshell (4d10) and a single electron in the 5s subshell (5s1). Despite this seemingly stable configuration, silver can adopt different oxidation states, such as 1 and 2, where electrons are lost from either the 5s or 4d orbitals.

Transition State Behavior

In its 1 oxidation state, silver loses one electron from the 5s orbital, resulting in the configuration:

[Kr] 4d10

In the 2 oxidation state, it loses an additional electron from the 4d orbital, leading to:

[Kr] 4d9

This ability to lose electrons from the d orbitals and adopt various oxidation states is a hallmark of transition metals. In its 2 state, silver exhibits a partially filled d subshell (4d9).

IUPAC Definition of Transition Elements

In accordance with the IUPAC (International Union of Pure and Applied Chemistry) definition, a transition element is one that either has an incomplete d subshell or can give rise to cations with an incomplete d subshell. [1]

Chemical Traits and Transition Behavior

Much like other transition metals, silver demonstrates unique chemical traits that set it apart from other elements. These traits include:

The ability to use both the outermost s and d orbitals for bonding. The flexibility in bonding with various elements to form diverse compounds.

While silver does not strictly meet the first criterion (having an incomplete d subshell in its ground state), it satisfies the second criterion through its 2 oxidation state. In this state, it shows a considerable degree of transition element behavior.

The classification of silver as a transition element underscores the importance of promoting a flexible understanding of electron configurations and oxidation states when defining and analyzing chemical properties. This flexibility is a defining feature of transition metals, making them indispensable in numerous chemical and technological applications.

References

[1] IUPAC, Compendium of Chemical Terminology, 2nd ed. (the Gold Book). Online.