Molybdenum (Mo): Atomic Structure and Chemical Properties

Atomic Model Details of Molybdenum (Mo)

Molybdenum (Mo) is a d-block transition element.

Atomic Number (Z): 42
Mass Number (A): Approximately 95.96 u (atomic mass of naturally occurring Molybdenum, dominated by isotopes like ⁹⁸Mo).
Number of Protons: 42
Number of Electrons: 42 (in a neutral atom)
Number of Neutrons: Varies by isotope. For the most abundant isotope ⁹⁸Mo, there are 98 - 42 = 56 neutrons. For the average atomic mass, approximately 95.96 - 42 = 53.96 neutrons.
Atomic Radius (Covalent): 139 pm

Molybdenum exhibits an exception to the Aufbau principle due to the enhanced stability of a half-filled d-subshell.

Electronic Configuration: [Kr] 4d⁵ 5s¹
- This configuration provides maximum spin multiplicity for the d-subshell (half-filled) and a single electron in the 5s subshell, leading to greater stability compared to [Kr] 4d⁴ 5s².
Shell Diagram (Electron Distribution):
- K-shell (n=1): 2 electrons (1s²)
- L-shell (n=2): 8 electrons (2s² 2p⁶)
- M-shell (n=3): 18 electrons (3s² 3p⁶ 3d¹⁰)
- N-shell (n=4): 13 electrons (4s² 4p⁶ 4d⁵)
- O-shell (n=5): 1 electron (5s¹)
- Total Electrons: 2 + 8 + 18 + 13 + 1 = 42 electrons.

As a transition metal, Molybdenum exhibits specific periodic trends.

The energy required to remove an electron from a gaseous atom.

First Ionization Enthalpy (IE₁): 684.3 kJ/mol
Second Ionization Enthalpy (IE₂): 1560 kJ/mol
Trend: Relatively low due to metallic character, but higher than alkali or alkaline earth metals. Increases across a period due to increasing effective nuclear charge.

A measure of an atom’s ability to attract electrons in a chemical bond (Pauling scale).

Pauling Electronegativity: 2.16
Trend: Molybdenum is moderately electronegative, typical for a transition metal. It is higher than elements to its left in the periodic table but lower than non-metals to its right.

The energy change when an electron is added to a neutral gaseous atom to form an anion.

Electron Gain Enthalpy: -72 kJ/mol
Trend: Molybdenum has a slightly negative electron gain enthalpy, indicating a small amount of energy is released upon accepting an electron. This is typical for metals, which generally have less affinity for electrons than non-metals.

The distance from the center of the nucleus to the outermost electron shell.

Covalent Atomic Radius: 139 pm
Trend: Atomic radius generally decreases across a period (due to increasing effective nuclear charge) and increases down a group (due to addition of new electron shells). Molybdenum’s radius is relatively stable within its period due to the d-block contraction effect.