The element with 25 electrons in a neutral atom is Manganese (Mn). The number of electrons in a neutral atom corresponds directly to its atomic number, \(Z=25\). Manganese is a metallic element that is an indispensable component in both industrial applications and biological processes.
Identification of the Element
The identity of a chemical element is defined by the number of protons within its nucleus, known as the atomic number (\(Z\)). Since a neutral atom has an equal number of electrons and protons, an atom with 25 electrons must have 25 protons, identifying it as Manganese. Manganese has an atomic weight of approximately 54.94 atomic mass units (u).
Manganese is classified as a transition metal, occupying Group 7 and Period 4 on the periodic table. This position places it within the first transition series, characterized by the filling of the \(d\)-orbitals. This placement dictates the element’s distinct physical and chemical characteristics. As a pure metal, Manganese is hard and brittle, limiting its practical use in its unalloyed form.
Electron Arrangement and Atomic Structure
The 25 electrons in a Manganese atom are distributed across various energy levels and orbitals. Its full electron configuration is \(1s^2 2s^2 2p^6 3s^2 3p^6 3d^5 4s^2\). Using the noble gas shorthand, the configuration is \([\text{Ar}] 4s^2 3d^5\).
The valence electrons, those involved in chemical bonding, are found in the outermost \(4s\) orbital and the partially filled \(3d\) orbital, totaling seven valence electrons. The \(3d^5\) configuration is noteworthy because a half-filled \(d\)-subshell provides extra stability to the atom, a concept derived from Hund’s rule. This half-filled state contributes to the magnetic properties of Manganese, resulting in five unpaired electrons. When forming ions, the two electrons from the \(4s\) orbital are removed before any \(3d\) electrons.
Core Chemical Behavior
The defining chemical characteristic of Manganese is its exceptional variability in oxidation states, ranging from \(-3\) to \(+7\). The most common and stable states are \(+2, +3, +4, +6\), and \(+7\), which arise from the small energy difference between the \(4s\) and \(3d\) orbitals. The \(+2\) state is particularly stable because the resulting \(\text{Mn}^{2+}\) ion has a half-filled \(3d^5\) configuration, providing enhanced stability.
The \(+4\) oxidation state is found in Manganese dioxide (\(\text{MnO}_2\)), a brownish-black solid used extensively in batteries and as an oxidizing agent. The highest oxidation state, \(+7\), is present in the intensely purple permanganate ion (\(\text{MnO}_4^-\)), often encountered as potassium permanganate (\(\text{KMnO}_4\)). This compound is a powerful oxidizer, utilized in water purification and as a laboratory reagent.
Vital Roles in Nature and Industry
Manganese is an indispensable element across numerous sectors; approximately 90% of its global production is used in metallurgy. It is a fundamental additive in steel production, where it acts as a deoxidizer and desulfurizer, preventing the formation of iron sulfide and enhancing the strength, hardness, and durability of the steel. Small additions of Manganese also improve the corrosion resistance and mechanical properties of aluminum and copper alloys, notably in beverage cans.
Manganese is recognized as an essential trace nutrient for all life forms. In plants, it is a structural component of the oxygen-evolving complex, responsible for splitting water molecules during photosynthesis. In humans and animals, Manganese serves as a cofactor for several enzymes, including Manganese superoxide dismutase (\(\text{MnSOD}\)), which protects cells from oxidative damage. The element plays a role in various metabolic functions, such as energy regulation, bone development, and neurotransmitter synthesis.