Question

Write the ground-state electron configurations of the following transition metal ions: (a) \(\mathrm{Sc}^{3+},(\mathrm{b}) \mathrm{Ti}^{4+}\) (c) \(\mathrm{V}^{5+}\) (e) \(\mathrm{Mn}^{2+},(\mathrm{f}) \mathrm{Fe}^{2+},(\mathrm{g}) \mathrm{Fe}^{3+}\) (d) \(\mathrm{Cr}^{3+}\) (h) \(\mathrm{Co}^{2+}\) (i) \(\mathrm{Ni}^{2+},(\mathrm{j}) \mathrm{Cu}^{+},(\mathrm{k}) \mathrm{Cu}^{2+},\) (l) \(\mathrm{Ag}^{+}\) \((\mathrm{m}) \mathrm{Au}^{+},(\mathrm{n}) \mathrm{Au}^{3+},(\mathrm{o}) \mathrm{Pt}^{2+}\)

Short answer

Remove electrons starting from the outermost energy level, following exceptions for stability.

Step-by-step solution

Determine Neutral Atom Configuration

Begin by finding the electron configuration of the neutral atom of each transition metal. Use the order of filling which usually follows the Aufbau principle (e.g., for Scandium, Sc: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹).

Identify the Ion's Charge

For each ion, identify the charge. This tells us how many electrons we need to remove from the neutral atom's configuration. For example, Scandium has an ion configuration of \(\text{Sc}^{3+}\) indicating a loss of 3 electrons.

Remove Electrons from Highest Energy Level

Remove the given number of electrons, starting from the outermost shell (highest sublevel) first, typically starting from the 4s orbital and then from the 3d. For \(\text{Sc}^{3+}\), remove three electrons from 4s² 3d¹ to get 1s² 2s² 2p⁶ 3s² 3p⁶.

Repeat for Each Ion

Apply the above steps for each ion. For example, for \(\text{Ti}^{4+}\), start with Ti: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d² and remove four electrons to get 1s² 2s² 2p⁶ 3s² 3p⁶. Repeat similarly for others.

Note Common Exceptions

There are exceptions to the standard order of filling, such as half-filled and filled d sublevels being more stable (e.g., \(\text{Cu}^+\) and \(\text{Cr}^{3+}\)). For Cu⁺, remove from 4s: Cu: [Ar] 4s¹ 3d¹⁰ → Cu⁺: [Ar] 3d¹⁰.

Key concepts

Ground-State Electron Configuration

The ground-state electron configuration is essentially a way of describing how electrons are distributed within an atom's orbitals when the atom is at its lowest energy state. Knowing the electron configuration helps in understanding the chemical properties and reactivity of elements.
For transition metals, the ground-state electron configuration typically involves the filling of the 3d sublevel after the 4s orbital, leading to configurations such as for Scandium (Sc), which has a configuration of 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹. This configuration reflects the natural order in which electrons fill up available spaces around an atom's nucleus.

Aufbau Principle

The Aufbau principle, from the German "building up," is a rule used to determine the electron configuration of an atom. According to this principle, electrons fill up orbitals from the lowest to the highest energy.
This filling order allows us to understand why the 4s orbital is filled before the 3d orbital in transition metals. The principle serves as a guideline for predicting the ground-state electron configurations of atoms, starting from the hydrogen atom up to more complex elements. This systematic filling of orbitals is crucial for correctly determining the electron distributions in neutral atoms.

Electron Removal from Highest Energy Level

When forming ions, especially transition metal ions, electrons are removed to account for the positive charge. It is important to note here that removal begins from the highest energy level. In transition metals, this typically means removing electrons from the 4s orbital before the 3d.
For example, Scandium ( ext{Sc}^{3+}), which loses three electrons, removes its 4s² electrons first and one from the 3d orbital, resulting in a configuration of 1s² 2s² 2p⁶ 3s² 3p⁶. This process follows the principle that outmost electrons, which are least tightly bound, will be removed first.

Transition Metals

Transition metals are a group of elements found in the d-block of the periodic table, specifically known for having partially filled d-orbitals. These metals are distinct for their bright colors, magnetic properties, and ability to form varied oxidation states.
The ability of transition metals to exist in multiple oxidation states is because the d and s orbitals are close in energy, allowing electrons to be removed from both, thus reinfecting their ionization characteristics. This flexibility in arrangements allows them to create complex and diverse chemistry, making them pivotal in both industrial applications and biological systems.

Ion Charge Determination

Determining the charge of a transition metal ion involves understanding how many electrons have been removed relative to the neutral atom. The ion's charge is positive because it represents missing electrons relative to the atomic form.
If an atom like Titanium (Ti) sheds four electrons to become ext{Ti}^{4+}, then the specific electron configuration must reflect these lost electrons, looking like 1s² 2s² 2p⁶ 3s² 3p⁶ after removing electrons from the 4s and 3d orbitals. Knowing an ion's charge is essential to predict its chemical behavior and the compounds it may form.