Manganese (Mn) Revision Guide

Atomic Model Details

Manganese (Mn) is a chemical element with atomic number 25.

Atomic Number (Z): 25
Mass Number (A): Approximately 55 (specifically, for the most abundant isotope, $^\{55\}$Mn, it is 54.9380 u).
Protons: 25
Electrons: 25 (in a neutral atom)
Neutrons: 30 (for $^\{55\}$Mn isotope, calculated as A - Z = 55 - 25)
Atomic Radius (Metallic): 127 pm (picometers)
Atomic Radius (Covalent): 139 pm

Electronic Configuration & Shell Diagram

Manganese belongs to the d-block elements, specifically group 7, period 4 of the periodic table.

Full Electronic Configuration: $1s^2 2s^2 2p^6 3s^2 3p^6 3d^5 4s^2$
Condensed Electronic Configuration: $[Ar] 3d^5 4s^2$

Shell Diagram Representation: Electrons are distributed in concentric shells around the nucleus as follows:

K-shell (n=1): 2 electrons ($1s^2$)
L-shell (n=2): 8 electrons ($2s^2 2p^6$)
M-shell (n=3): 13 electrons ($3s^2 3p^6 3d^5$)
N-shell (n=4): 2 electrons ($4s^2$)

The presence of five unpaired electrons in the 3d subshell and two electrons in the 4s subshell is characteristic. The half-filled 3d subshell ($3d^5$) contributes to the relative stability of the atom and its tendency to exhibit various oxidation states.

Periodic Trends

The position of Manganese in the periodic table dictates several of its fundamental chemical properties.

Ionization Enthalpy

Ionization enthalpy is the energy required to remove an electron from a gaseous atom or ion.

First Ionization Enthalpy (IE1): 717 kJ/mol (Energy required to remove the first electron, typically from the $4s$ subshell).
Second Ionization Enthalpy (IE2): 1509 kJ/mol (Energy required to remove the second electron).
Third Ionization Enthalpy (IE3): 3248 kJ/mol (Energy required to remove the third electron). The relatively high IE3 is due to removing an electron from the stable half-filled $3d^5$ configuration (after $4s^2$ and one $3d$ electron are removed).

Electronegativity

Electronegativity is a measure of the tendency of an atom to attract a shared pair of electrons.

Pauling Scale Electronegativity: 1.55 Manganese has an intermediate electronegativity, typical for transition metals, indicating its ability to form compounds with both electropositive and electronegative elements.

Electron Gain Enthalpy

Electron gain enthalpy is the energy change when an electron is added to a neutral gaseous atom to form an anion.

Electron Gain Enthalpy: Approximately +50 kJ/mol (slightly positive or endothermic). For most metals, especially transition metals like Manganese, the electron gain enthalpy is typically positive or very close to zero, meaning energy must be supplied to add an electron. This reflects their tendency to lose rather than gain electrons to achieve stability.

Atomic Radius

Atomic radius refers to the size of the atom.

Metallic Radius: 127 pm
Covalent Radius: 139 pm As a transition metal, Manganese exhibits a relatively small decrease in atomic radius across the period due to the shielding effect of the d-electrons and the increasing nuclear charge.

Key Physical Properties

Manganese is a hard, brittle, silvery-grey metal.

Density: 7.47 g/cm³ at 20 °C.
State at Room Temperature: Solid.
Color: Silvery-grey, often with a metallic luster. It is a brittle metal.
Melting Point: 1246 °C (1519 K).
Boiling Point: 2061 °C (2334 K). Manganese exhibits several allotropic forms, each with distinct physical properties, but the values above generally refer to the most common $\alpha$-Manganese allotrope.