Problem 106 - Chemistry Matter and Change

Question

Discuss the formation of the nickel ion with a 2+ oxidation number.

Step-by-Step Solution

Answer

The nickel ion with a 2+ oxidation number (Ni²⁺) is formed by removing two electrons from the 4s orbital of a nickel atom, which has the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁸. The resulting Ni²⁺ ion has a more stable electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁸, with completely filled 3p and half-filled 3d orbitals. This stability enables Ni²⁺ ions to participate in various chemical compounds, such as nickel(II) chloride (NiCl₂), nickel(II) sulfate (NiSO₄), and nickel(II) oxide (NiO).

Step 1: Identify the electron configuration of the nickel atom

Nickel (Ni) has an atomic number of 28, which means it has 28 electrons. The electron configuration of a nickel atom can be determined by filling the electron orbitals according to the Aufbau principle. The electron configuration for nickel is: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁸

Step 2: Understand the formation of nickel ion with a 2+ oxidation number

To form the nickel ion with a 2+ oxidation number, nickel has to lose two electrons. The loss of electrons is most likely to occur from the outermost shells. In this case, electrons are removed first from the 4s orbital. Ni loses 2 electrons: 4s² → 4s⁰ The electron configuration of the nickel ion with a 2+ oxidation number (Ni²⁺) will be: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁸

Step 3: Explain the stability of the nickel ion with a 2+ charge

The formation of the nickel ion with a 2+ charge gives it a more stable electron configuration with a completely filled 3p orbital and a half-filled 3d orbital. In general, transition metal ions with filled or half-filled d orbitals are more stable in their compounds. This is why nickel prefers to form a 2+ ion in many of its chemical compounds.

Step 4: State examples of compounds containing Ni²⁺ ions

There are many compounds which contain nickel ions with a 2+ oxidation number. Some examples include: 1. Nickel(II) chloride (NiCl₂): a commonly used nickel(II) salt. 2. Nickel(II) sulfate (NiSO₄): used in electroplating and other applications. 3. Nickel(II) oxide (NiO): a compound used in the production of various pigments and batteries. These examples demonstrate the versatile nature of the nickel (II) ion in forming a range of compounds. In summary, the nickel(II) ion is formed by the removal of two electrons from the 4s orbital in the nickel atom, leading to a more stable electron configuration and allowing it to participate in the formation of a range of chemical compounds.

Key Concepts

Electron Configuration

Understanding electron configuration is crucial when discussing the formation of ions, especially for transition metals like nickel. Electron configuration refers to the distribution of electrons in an atom's orbitals. For nickel, this is represented by the notation 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁸, indicating that the 3d and 4s orbitals are the outermost orbitals. When an atom transforms into an ion, it usually loses electrons from these outermost shells. The transition metal characteristic of having incompletely filled d orbitals becomes significant. Upon losing two electrons to form a Ni²⁺ ion, nickel attains a configuration of 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁸.

This process, guided by the principles of quantum mechanics and the Aufbau principle, ensures that each electron occupies the lowest energy orbital available. As a result, for the nickel ion, the stabilization is attributed to a fully occupied 3p orbital and a sort of stability by having a symmetrical distribution in the 3d orbital. This electron arrangement is particularly important for predicting the chemical behavior and bonding capabilities of the nickel ion.

Oxidation Number

When we talk about a nickel ion with a 2+ oxidation number, we are referring to its oxidation state, which is a measure of the degree of oxidation or loss of electrons. The oxidation number for nickel in its ionized form is +2, implying that it has lost two electrons. This loss leads to a positive charge since electrons are negatively charged, and the removal of two negatively charged electrons leaves an imbalance of charge in favor of protons.

The oxidation number is crucial in predicting the types of chemical reactions nickel can undergo. For instance, an oxidation number of +2 suggests that nickel can engage in oxidation-reduction (redox) reactions as it has the potential to either accept more electrons and reduce its oxidation number or lose more electrons and increase its oxidation number. Understanding the oxidation state helps in determining the formulas of compounds formed and in constructing and balancing chemical equations. The stability of a +2 oxidation state in nickel is a common feature in chemistry, especially for transition metal ions, due to the energy considerations and the resulting stable electron configurations.

Transition Metals

Nickel is part of the transition metals, a group characterized by their ability to form variable oxidation states and complex ions. Moreover, they often have incompletely filled d orbitals, which can participate in bonding and result in unique chemical and physical properties. Transition metals are well known for their roles in colorful compounds, catalysis, and materials with magnetic properties.

Nickel, when forming a 2+ ion, exhibits these typical transition metal behaviors. It can form various coordination complexes where the Ni²⁺ ion is at the center, surrounded by other atoms or molecules, known as ligands. The variety of compounds that contain Ni²⁺ ions, such as nickel(II) chloride, nickel(II) sulfate, and nickel(II) oxide, highlights the versatility of nickel as a transition metal. Each compound showcases different aspects of nickel's chemistry, from its role in electroplating to its use in producing batteries and pigments. The 2+ oxidation state, while stable and common, is not the only oxidation state nickel can adopt, but it is the one that illustrates the quintessential characteristics of transition metal chemistry—complex formation, varied oxidation states, and involvement in diverse industrial applications.