Question

The heats of atomization, \(\Delta H_{\text {atom }}\), in \(\mathrm{kJ} / \mathrm{mol}\), of the first transition series of elements are as follows: (a) Write an equation for the process involved in atomization, and describe the electronic and structural changes that occur. (b) \(\Delta H_{\text {atom }}\) varies irregularly in the series following \(\mathrm{V}\). How can this be accounted for, at least in part, using the electronic configurations of the gaseous atoms? (Hint: Recall the discussions of Sections \(6.8\)

Short answer

(a) Atomization is the process of converting an element in its solid-state into individual gaseous atoms, represented by the equation: \(M(s) \rightarrow M(g)\). During atomization, metallic bonds are broken and electronic configurations may change due to redistribution of electrons. (b) The irregular variation in \(\Delta H_{\text {atom}}\) values in the first transition series after Vanadium (V) can be attributed to the subtle interplay of screening effects and electron-electron repulsion between the 3d and 4s electrons. Factors such as relative instability of higher oxidation states and variations in d orbital filling or emptying contribute to the variation. Chromium's unique configuration ([Ar] \(3d^5 4s^1\)) provides extra stability due to exchange energy, requiring higher energy for atomization.

Step-by-step solution

Define atomization and equation

Atomization refers to the process of converting an element in its solid-state into individual gaseous atoms. The equation for the process can be represented as: \[M(s) \rightarrow M(g)\] Here, 'M' denotes the element in question, and (s) and (g) represent its solid and gaseous states, respectively.

Describe electronic and structural changes

During atomization, an element in its solid-state undergoes several electronic and structural changes while converting into gaseous atoms. These changes include: 1. Breaking of metallic bonds: As we move from solid to the gaseous state, the metallic bonds that hold the lattice structure are broken. This typically requires the absorption of energy. 2. Change in electronic configuration: In some cases, the electronic configuration of the element in its gaseous state might differ slightly from its solid-state, owing to redistribution of electrons among available orbitals.

Analyze the irregular variation in \(\Delta H_{\text {atom}}\) values after Vanadium (V)

To analyze the irregular variation in \(\Delta H_{\text {atom}}\) values in the first transition series after Vanadium (V), we need to examine the electronic configurations. Considering Cr (Chromium), following V, we find that it has a special configuration of [Ar] \(3d^5 4s^1\) as compared to the general configuration of [Ar] \(3d^n 4s^{(2-n)}\). This is because the half-filled 3d sub-shell in the case of Chromium provides extra stability, owing to the phenomenon of exchange energy. Hence, a higher energy is required to break these extra stable electronic configurations, which results in a higher value of atomization energy.

Evaluate electronic configurations for other elements in the first transition series

Upon evaluating electronic configurations for other elements in the first transition series, we find that these variations are primarily due to the subtle interplay of screening effects and electron-electron repulsion between the 3d and 4s electrons. The irregularity in \(\Delta H_{\text {atom}}\) values can be attributed to: 1. Relative instability of higher oxidation states for heavier elements in the series. 2. Incomplete filling or emptying of the d orbitals in some cases, which affects the overall stability and bonding characteristics of the elements. By considering these factors and electronic configurations, we can account for the irregular variation in the heats of atomization in the first transition series following Vanadium (V).

Key concepts

Electronic Configuration

Electronic configuration plays a fundamental role in understanding the properties of elements, especially within the transition series. Transition metals exhibit varied electron arrangements due to their 3d and 4s orbitals. The order in which these orbitals fill can significantly influence an element's chemical behavior and properties.

Typically, electrons fill the 4s orbital before the 3d. However, once filled, the 3d orbital becomes lower in energy, affecting the distribution of electrons. This is why certain transition metals deviate from expected configurations, such as Chromium ([Ar] 3d⁵ 4s¹) and Copper ([Ar] 3d¹⁰ 4s¹).

For students, recognizing these deviations is essential, as they often explain the unique chemical and physical characteristics of these elements, including their magnetic properties and bonding energies.

Metallic Bonding

Metallic bonding is crucial in understanding the structural integrity of metals in their solid state. In transition metals, these strong bonds account for many of their characteristic properties. Metallic bonds involve the sharing of free electrons among a lattice of metal cations, which allows for both strength and conductivity.

As metals transition from a solid to a gaseous state during atomization, these bonds must be overcome. The energy required to break these bonds is reflected in the heat of atomization, \(\Delta H_{\text{atom}}\). This process drives the study of electronic configuration and stability across the series.

Understanding metallic bonding is fundamental for comprehending how transition metals change forms and how their structural adaptations impact their roles in chemistry.

Exchange Energy

Exchange energy emerges as a crucial concept when examining the stability of electron arrangements in transition metals. It is the additional stability that results from the exchange of electrons with parallel spins in a subshell. This is especially significant in partially filled d-orbitals.

For instance, Chromium holds a unique electronic configuration due to exchange energy: [Ar] 3d⁵ 4s¹. This configuration offers maximum exchange energy due to the parallel spinning and symmetry of half-filled 3d orbitals.

• Ensures maximum unpaired electrons.
• Provides extra stability to the atom.

Comprehending exchange energy is vital for understanding why some transition metals require more energy for processes like atomization, influencing their chemical reactivity and stability.

3d and 4s Orbitals

The 3d and 4s orbitals are central to understanding the complex behaviors of transition metals. Their unique electron configurations arise from the energy similarities between these two orbitals. Ordinarily, electrons may first fill the 4s orbital due to its slightly lower energy, but upon filling, the 3d becomes more stable.

In metals like Chromium and Copper, we observe anomalous fillings:

• Chromium: [Ar] 3d⁵ 4s¹
• Copper: [Ar] 3d¹⁰ 4s¹

These configurations maximize stability, thanks to either half-filled or fully filled 3d orbitals, which are more stable configurations.

Understanding these orbital interactions is pivotal for chemistry students to predict reactivity, bonding, and properties of transition metals.