Question

A \(\mathrm{M}^{2+}\) ion derived from a metal in the first transition metal series has four electrons in the \(3 d\) subshell. What element might \(\mathrm{M}\) be?

Short answer

The element is iron (Fe).

Step-by-step solution

Understanding the Problem

The question asks us to identify a transition metal that becomes a \(\mathrm{M}^{2+}\) ion, which implies it loses two electrons to achieve this oxidation state. We need to find an element that, after losing 2 electrons, still has 4 electrons in its \{3d\} subshell.

Identifying the Original Electron Configuration

Transition metals have electrons in their \(3d\) subshell. For a \(\mathrm{M}^{2+}\) ion to have 4 electrons in \(3 d\), the neutral atom must have had 4 + 2 = 6 electrons in the \(3d\) subshell before losing the 2 electrons.

Locating the Element in the Periodic Table

The arrangement of electrons for transition metals is determined by their position in the periodic table. Specifically, the element with the electron configuration ending in \(3d^6 4s^2\) when neutral is iron (Fe), which is element number 26.

Synthesis: Determining the Metal

When this element loses two electrons to become \(\mathrm{Fe}^{2+}\), those two electrons are typically removed from the \(4s\) subshell first, then \(3d\). Thus, the configuration becomes \(3d^6\). Since the \(\mathrm{Fe}^{2+}\) ion exactly matches having 6 electrons in \(3d\), the metal \(\mathrm{M}\) is indeed iron (Fe).

Key concepts

Electron Configuration

The electron configuration of an element provides a way to know the arrangement of electrons in an atom. For transition metals, their unique properties are largely influenced by the electrons in the d subshells. Transition metals are renowned for having partially filled d subshells, which gives them distinct characteristics.

For a neutral atom, electrons fill the orbitals in a specific order, starting with the lowest energy levels. In general, the 4s subshell is filled before the 3d subshell, even though it is emptied before the 3d subshell when electrons are removed. Therefore, for neutral transition metals, electron filling follows the order of 3d and then 4s.

• The total electron configuration accounts for all electrons in an atom and shows their arrangement across the various subshells.
• For iron (Fe), the electron configuration when neutral is typically written as \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^6\).
• When a transition metal forms a positive ion, electrons are usually lost. The 4s electrons are lost first followed by the 3d electrons.

Understanding electron configuration helps us identify the properties of transition metals, such as their ability to form various ions.

Oxidation States

The oxidation state of an atom is a number that represents its ability to acquire, donate, or share electrons when forming a chemical bond. Transition metals commonly have multiple oxidation states because they have nearly equal energy levels in their 3d and 4s subshells.

Transition metals can lose different numbers of electrons to achieve these states. Iron (Fe), for example, showcases a variety of oxidation states, but is most commonly found in the +2 and +3 states, known as \( ext{{Fe}}^{2+} \) and \( ext{{Fe}}^{3+} \), respectively.

• In the +2 oxidation state, two electrons are typically lost from the 4s orbital.
• This leads to the configuration changing from \(3d^6 4s^2\) to \(3d^6\) as seen in the \( ext{{Fe}}^{2+} \) ion.

The capability of transition metals to have multiple oxidation states is a fundamental reason why they are versatile in their chemical reactions and bonding behaviors.

Periodic Table Position

The periodic table is a tabular representation of chemical elements, organized based on atomic number, electron configurations, and recurring chemical properties. The position of an element on the table can tell us volumes about its properties and behaviors.

Transition metals are located in the d-block of the periodic table, between groups 3 and 12. Each of these elements has partially filled d orbitals. Iron (Fe), for example, is in the fourth period and is the sixth element in the transition series, placing it in group 8.

• The position of iron in the periodic table shows it as a typical transition metal.
• This position helps explain its magnetic properties, capacity to form colorful compounds, and its role as a key player in biochemistry.

Period, group, and block information from the periodic table helps predict an element's electronic configuration and its typical chemical behavior. Understanding these aspects for elements like iron allows insight into why they are widely used in various industrial and biological processes.