(a) What is the general rule concerning the order in which electrons are removed from a transition metal atom to form an ion? Give an example from Group \(5 \mathrm{~B}(5) .\) (b) Name two types of measurements used to study electron configurations of ions.

When forming ions from transition metals, electrons are removed following a specific rule known as the **electron removal rule**. This rule states that electrons are removed **first** from the orbital with the highest principal quantum number. Typically, this means electrons are yanked out from the 4s orbital before the 3d orbital, even though the 3d orbital was filled before the 4s during electron configuration of the neutral atom.

For example, in vanadium (V), the electron configuration is [Ar]3d^3 4s^2. Upon ionization, vanadium loses electrons from the 4s orbital first. When forming vanadium ions like V^2+, it would have lost two electrons from the 4s orbital, resulting in a configuration of [Ar] 3d^3.

Understanding the energy levels of orbitals is crucial in electron configuration. Orbital energy levels tell us which orbital electrons will occupy first. In isolated atoms, electrons fill the lowest energy orbitals first, known as the **Aufbau principle**.

For transition metals, 4s and 3d orbitals are key. Even though 3d orbitals are filled after 4s orbitals during electron configuration for neutral atoms, the 4s electrons are of higher energy and are removed first when the atom ionizes.

This nuanced behavior is due to the relative energies and shielding effects within the atom's electronic structure.

**X-ray photoelectron spectroscopy (XPS)** is an important technique used to study electron configurations of atoms and ions. It measures the binding energies of electrons. By irradiating a material with X-rays, XPS can kick out electrons from their orbitals.

The kinetic energy of these emitted electrons is measured, and from this, the binding energy can be calculated. Binding energies tell us about the specific orbital electrons occupy and can reveal changes in the electronic structure when an atom forms ions by losing or gaining electrons. XPS can, therefore, provide detailed insights into the nature of orbitals in both neutral and ionized states.

Another essential tool for studying electron configurations, particularly in ions, is **electron paramagnetic resonance (EPR)**. This technique is useful for studying materials with unpaired electrons. It's based on the fact that unpaired electrons have magnetic moments which can interact with an external magnetic field.

EPR spectroscopy detects these interactions and provides information about the electronic environment of the unpaired electrons. This insight helps scientists understand the specifics of electron configurations, especially in transition metal ions where unpaired electrons are common.

Transition metals are elements found in the d-block of the periodic table and are known for their ability to form various ionized states. These elements have partially filled d orbitals that allow them to exhibit multiple oxidation states.

When transition metals form ions, they lose electrons from their 4s orbital first, followed by the 3d orbital. This property distinguishes them from the main group elements.

For example, iron (Fe) can lose two electrons to form Fe^2+ with the electron configuration [Ar]3d^6, or three electrons to form Fe^3+ with the configuration [Ar]3d^5. This variability in oxidation states makes transition metals very versatile and vital in numerous chemical processes and industrial applications.