Problem 90 - Chemistry An Atoms First Approach

Question

The first-row transition metals from chromium through zinc all have some biologic function in the human body. How many unpaired electrons are present in each of these first-row transition metals in the ground state?

Step-by-Step Solution

Answer

The ground state unpaired electron count for the first-row transition metals from Chromium (Cr) through Zinc (Zn) are: Cr: 5, Mn: 5, Fe: 4, Co: 3, Ni: 2, Cu: 0, and Zn: 0.

Step 1: Identify the elements in the first-row transition metals

The first-row transition metals are elements with atomic numbers 24 through 30, corresponding to Chromium (Cr) through Zinc (Zn).

Step 2: Write their electron configurations

Using the periodic table, fill up the electron orbitals by the Aufbau principle, Hund's rule, and Pauli Exclusion Principle. The configurations of the first-row transition metals are: Cr: \([Ar]\) 4s\(^1\) 3d\(^5\) Mn: \([Ar]\) 4s\(^2\) 3d\(^5\) Fe: \([Ar]\) 4s\(^2\) 3d\(^6\) Co: \([Ar]\) 4s\(^2\) 3d\(^7\) Ni: \([Ar]\) 4s\(^2\) 3d\(^8\) Cu: \([Ar]\) 4s\(^1\) 3d\(^{10}\) Zn: \([Ar]\) 4s\(^2\) 3d\(^{10}\)

Step 3: Determine the number of unpaired electrons

To find the number of unpaired electrons, examine the d orbitals in the electron configurations: Cr: 3d\(^5\): Five unpaired electrons Mn: 3d\(^5\): Five unpaired electrons Fe: 3d\(^6\): Four unpaired electrons Co: 3d\(^7\): Three unpaired electrons Ni: 3d\(^8\): Two unpaired electrons Cu: 3d\(^{10}\): Zero unpaired electrons Zn: 3d\(^{10}\): Zero unpaired electrons The ground state unpaired electron count for the first-row transition metals is 5, 5, 4, 3, 2, 0, and 0.

Key Concepts

Electron Configuration

Electron configuration is a way to describe the arrangement of electrons around the nucleus of an atom. This arrangement is crucial as it helps determine the chemical properties of an element. For transition metals like chromium through zinc, the electron configuration particularly involves the filling of 'd' orbitals.

• Chromium (Cr) starts with an unusual arrangement: \([Ar]\) 4s\(^1\) 3d\(^5\). Normally, you'd expect it to be 4s\(^2\) 3d\(^4\), but stability is gained with half-filled d orbitals.
• As you move along to manganese (Mn) and then to zinc (Zn), electrons progressively fill the 3d orbitals, passing through configurations like 3d\(^5\), 3d\(^6\), and so forth.

By understanding electron configurations, you begin to see patterns in reactivity and bonding, making electron configuration a cornerstone of both chemistry and physics.

Unpaired Electrons

Unpaired electrons are those electrons in an atom that are alone in an orbital, making them significant contributors to an element's magnetic properties. In transition metals, the number of unpaired electrons can vary greatly due to how electrons distribute among orbitals.

• For example, chromium and manganese both have five unpaired electrons, which contributes to their distinct magnetic properties.
• As we advance further through the period, the number of unpaired electrons decreases, resulting in differing magnetism.

Elements like copper (Cu) and zinc (Zn) have no unpaired electrons, which means they are diamagnetic—opposing external magnetic fields. Recognizing unpaired electrons in an element helps illustrate why certain metals are more magnetic than others.

Biologic Function

Transition metals often play vital roles in biological systems due to their diverse properties. In the human body, they contribute to a variety of functions primarily through their participation in enzymes and cofactors that drive biochemical reactions.

• For example, iron (Fe) is crucial for oxygen transport in blood through its role in hemoglobin.
• Zinc (Zn) is essential for immune function and metabolism, having roles in over 300 enzymes.

The ability of transition metals to exist in multiple oxidation states and to form complexes are key features that facilitate their biological roles. Therefore, understanding their electron configurations and unpaired electrons can also provide insights into their functionality in biological systems.