Question

Why does chromium exhibit several oxidation states in its compounds, whereas aluminum exhibits only the \(+3\) oxidation state?

Short answer

In conclusion, the electronic configurations of aluminum and chromium determine their oxidation states. Aluminum exhibits only the +3 oxidation state due to its three valence electrons (\(3s^2 3p^1\)) and attaining a stable noble gas configuration when it loses them. In contrast, chromium, with its valence electrons in the \(4s^1 3d^5\) orbitals, can lose different numbers of electrons from these orbitals, leading to various oxidation states, such as +2, +3, and +6, enabling it to participate in a variety of redox reactions and form diverse compounds.

Step-by-step solution

Electronic Configurations of Aluminum and Chromium

Aluminum has an atomic number of 13, so its electronic configuration is \(1s^2 2s^2 2p^6 3s^2 3p^1\). Chromium has an atomic number of 24, so its electronic configuration is \[1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^5\] (its configuration is an exception to the general trend).

Relating Electronic Configurations to Oxidation States

The oxidation state of an element is determined by the number of electrons it loses, gains, or shares when forming compounds. In the case of aluminum and chromium, both being metals, we are concerned with the number of electrons they lose.

Oxidation State of Aluminum

Aluminum has three valence electrons in its 3s and 3p orbitals (\(3s^2 3p^1\)). When aluminum loses these three electrons, it achieves a stable, full electron configuration of 1s² 2s² 2p⁶, which is the same as the noble gas Neon. Therefore, aluminum exhibits only the +3 oxidation state, forming Al³⁺ ions.

Oxidation States of Chromium

Chromium's valence electrons are in the 4s and 3d orbitals (\(4s^1 3d^5\)). Its electronic configuration is relatively stable due to the half-filled 3d orbital. However, Chromium can lose different numbers of electrons from the 4s and 3d orbitals, leading to various oxidation states. The most common oxidation states for chromium are +2, +3, and +6, although others are possible as well. The different oxidation states allow chromium to participate in redox reactions and form various compounds with unique properties. In conclusion, the electronic configurations of aluminum and chromium determine their oxidation states. Aluminum exhibits only the +3 oxidation state due to its three valence electrons, while chromium can exhibit several oxidation states as it can lose various numbers of electrons from its 4s and 3d orbitals.

Key concepts

Electronic Configuration

The concept of electronic configuration refers to the distribution of electrons in an atom's orbitals. Each element's configuration is unique and helps determine its chemical behavior. For instance, aluminum has an electronic configuration of \(1s^2 2s^2 2p^6 3s^2 3p^1\). This configuration reveals that aluminum has two core levels that are fully occupied and three valence electrons. Valence electrons reside in the outermost shell, which participates in chemical bonding.

Chromium, on the other hand, displays a more intricate electronic configuration of \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^5\). This is an exception to the general filling order due to the stability provided by a half-filled d subshell. The distribution of electrons within these orbitals impacts the possible oxidation states the element can exhibit.

Electronic configurations thus provide critical insights into potential chemical reactivity, which is especially relevant for determining oxidation states.

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom. They are significant because they directly participate in the formation of chemical bonds. For any given element, the number of valence electrons dictates how it will interact with other atoms, especially in terms of gaining, losing, or sharing electrons to achieve a noble gas configuration.

In aluminum, the valence electrons consist of three electrons situated in the 3s and 3p orbitals (\(3s^2 3p^1\)). When these valence electrons are lost, aluminum achieves a very stable electronic configuration (\(1s^2 2s^2 2p^6\)), resembling the noble gas neon. Consequently, aluminum commonly exhibits a \(+3\) oxidation state.

Chromium presents a different picture with its \(4s^1 3d^5\) configuration, revealing six valence electrons. The flexibility in electron loss from both the \(4s\) and \(3d\) orbitals allows chromium to exhibit multiple oxidation states such as \(+2\), \(+3\), and \(+6\). This variation enables chromium to form diverse compounds with distinct properties.

Redox Reactions

Redox reactions involve the transfer of electrons between atoms, and they are fundamental processes in chemistry that define how chemicals interact. The term "redox" is derived from reduction-oxidation reaction. Reduction refers to the gain of electrons, while oxidation refers to the loss of electrons. During these processes, elements can change their oxidation states.

The involvement of oxidation states is crucial. For example, aluminum in its compounds typically has a \(+3\) oxidation state, indicating it has lost three electrons in redox reactions to achieve this state. This uniform state is attributed to its three valence electrons.

Chromium, however, can participate in more varied redox reactions due to its ability to adopt multiple oxidation states, like \(+2\), \(+3\), and \(+6\). This happens because chromium can lose different numbers of electrons from its \(4s\) and \(3d\) orbitals. Thus, it can form compounds with varied properties and can interact with a wide array of chemicals. Redox reactions involving chromium are widely studied for their complexity and industrial applications.