Question

Which of the following has the maximum number of unpaired electrons? (a) \(\mathrm{Mg}^{2+}\) (b) \(\mathrm{Ti}^{3+}\) (c) \(\mathrm{V}^{3+}\) (d) \(\mathrm{Fe}^{2+}\)

Short answer

\(\mathrm{Fe}^{2+}\) has the maximum number of unpaired electrons (4).

Step-by-step solution

Determine Electron Configurations

To determine the number of unpaired electrons, first find the electron configurations of each ion. We need to consider the number of electrons in neutral atoms and subtract electrons based on their ion charge. \(\mathrm{Mg} = [\mathrm{Ne}]3s^2 \rightarrow \mathrm{Mg}^{2+} = [\mathrm{Ne}]\); \(\mathrm{Ti} = [\mathrm{Ar}]3d^24s^2 \rightarrow \mathrm{Ti}^{3+} = [\mathrm{Ar}]3d^1\); \(\mathrm{V} = [\mathrm{Ar}]3d^34s^2 \rightarrow \mathrm{V}^{3+} = [\mathrm{Ar}]3d^2\); \(\mathrm{Fe} = [\mathrm{Ar}]3d^64s^2 \rightarrow \mathrm{Fe}^{2+} = [\mathrm{Ar}]3d^6\).

Identify Unpaired Electrons

Using the electron configurations, identify unpaired electrons. \(\mathrm{Mg}^{2+} = 0 \) unpaired electrons, \(\mathrm{Ti}^{3+} = 1 \) unpaired electron, \(\mathrm{V}^{3+} = 2 \) unpaired electrons, and \(\mathrm{Fe}^{2+} = 4 \) unpaired electrons. In \([\mathrm{Ar}]3d^6\), 4 out of 6 electrons in the \(3d\) subshell are unpaired.

Compare the Unpaired Electrons

Compare the number of unpaired electrons in each ion: \(\mathrm{Mg}^{2+} = 0\), \(\mathrm{Ti}^{3+} = 1\), \(\mathrm{V}^{3+} = 2\), and \(\mathrm{Fe}^{2+} = 4\). The ion with the greatest number of unpaired electrons is \(\mathrm{Fe}^{2+}\), with 4 unpaired electrons.

Key concepts

Electron Configuration

Electron configuration is a way to represent the arrangement of electrons in an atom or ion. Each electron occupies a certain location called an "orbital." The electron configuration describes these positions using numbers and letters. The numbers indicate the energy levels and the letters refer to the shapes of orbitals: s, p, d, and f.
For example, the electron configuration of a neutral iron atom (Fe) is \([\mathrm{Ar}]3d^64s^2\).Here, \([\mathrm{Ar}]\) represents the inner core electrons, with the remaining electrons located in the 3d and 4s orbitals.
When an atom forms an ion, electrons are removed starting from the outermost level. For instance, when \(\mathrm{Fe}\) loses two electrons to become \(\mathrm{Fe}^{2+}\), its new electron configuration is \([\mathrm{Ar}]3d^6\). This is important because only electrons that are not paired (unpaired electrons) contribute to magnetic properties.
Identifying electron configurations allows us to understand chemical reactions, bonding capabilities, and magnetic properties of elements. This is foundational for analyzing substances in chemistry.

Transition Metals

Transition metals are elements found in the center of the periodic table, specifically in the d-block. These metals are unique due to their ability to form ions with varying charges and their interesting electron configurations that often have unpaired electrons. This makes them essential in various chemical reactions and applications.
Transition metals like titanium (Ti), vanadium (V), and iron (Fe) show variable oxidation states. This variability is due to the relatively small energy difference between their 3d and 4s orbitals. When these metals lose or gain electrons, they often do so from these outermost orbitals first. This adaptability is why transition metals are used in everything from structural materials to catalysts.
Additionally, the presence of unpaired electrons in the d sublevel contributes to the metal's magnetism and ability to form colorful compounds. Because these elements can hold several unpaired electrons, they are often involved in complex chemistry, like catalysis and coordination chemistry.

Ionization

Ionization refers to the process of adding or removing electrons from an atom or molecule, which gives it a positive or negative charge. The ease or difficulty of this process varies depending on the element involved and the electrons' initial configuration.
In transition metals, ionization typically involves the removal of electrons from the outermost orbitals, usually starting with s-orbital electrons followed by d-orbital electrons. For instance, in iron, forming a \(\mathrm{Fe}^{2+}\) ion involves removing electrons from \(4s\) and \(3d\) orbitals. The updated electron configuration aids in determining the number of unpaired electrons.
The number of unpaired electrons is significant because it affects how an ion interacts chemically and physically. For example, an ion like \(\mathrm{Fe}^{2+}\) has 4 unpaired electrons, making it more magnificent in terms of magnetism compared to \(\mathrm{Mg}^{2+}\), which has no unpaired electrons. This property is called paramagnetism, which is critical in magnetic and electric applications. Understanding ionization and its impact on unpaired electrons help anticipate the behaviors and uses of transition metals in various fields.