Antimony (Sb): Atomic Structure & Chemical Properties

Introduction to Antimony (Sb)

Antimony (Sb), derived from the Latin stibium, is a chemical element with atomic number 51. It is a metalloid belonging to Group 15 of the periodic table, known as the Pnictogens.

Atomic Model Details

Antimony’s atomic structure can be characterized as follows:

Fundamental Particles

• Atomic Number (Z): 51
  • This indicates 51 protons in the nucleus.
  • In a neutral antimony atom, there are 51 electrons.
• Atomic Mass (Average): 121.76 u
• Neutrons: The most abundant isotopes are $^{121}$Sb and $^{123}$Sb.
  • For $^{121}$Sb (abundance ~57.21%), number of neutrons = 121 - 51 = 70.
  • For $^{123}$Sb (abundance ~42.79%), number of neutrons = 123 - 51 = 72.

Atomic Size

• Covalent Radius: 139 pm (Picometers)
• Van der Waals Radius: 206 pm

Electronic Configuration & Shell Diagram

Electronic Configuration

The ground state electronic configuration of Antimony is [Kr] 4d¹⁰ 5s² 5p³.

• This configuration shows that Antimony has 5 valence electrons (2 from the 5s subshell and 3 from the 5p subshell), which are responsible for its chemical reactivity.
• The presence of fully filled 4d¹⁰ subshell indicates a stable inner core.

Shell Diagram Representation

The electron distribution in different shells (K, L, M, N, O) for Antimony (Z=51) is:

• K-shell (n=1): 2 electrons
• L-shell (n=2): 8 electrons (2s² 2p⁶)
• M-shell (n=3): 18 electrons (3s² 3p⁶ 3d¹⁰)
• N-shell (n=4): 18 electrons (4s² 4p⁶ 4d¹⁰)
• O-shell (n=5): 5 electrons (5s² 5p³)

This can be summarized as 2, 8, 18, 18, 5.

Periodic Trends

Antimony exhibits periodic properties characteristic of Group 15 elements and its position as a metalloid.

Ionization Enthalpy (First)

• Value: 834 kJ/mol
• Trend: As a p-block element, its ionization enthalpy is relatively high compared to s-block elements but lower than non-metals in the same period. It decreases down Group 15 compared to Nitrogen and Phosphorus, reflecting increasing atomic size and shielding effect.

Electronegativity

• Pauling Scale Value: 2.05
• Trend: Antimony is more electronegative than metals but less electronegative than typical non-metals like Nitrogen, Oxygen, and Fluorine. Electronegativity generally decreases down Group 15.

Electron Gain Enthalpy

• Value: -101 kJ/mol
• Trend: The negative value indicates that Antimony has a tendency to accept an electron, albeit with less energy release than typical non-metals. The magnitude generally becomes less negative (or more positive) down Group 15.

Atomic Radius

• Covalent Radius: 139 pm
• Trend: Atomic radius increases down a group due to the addition of new electron shells. Antimony’s atomic radius is larger than Phosphorus and Arsenic.

Key Physical Properties

Antimony is a brittle, silvery-white metalloid.

• Density: 6.697 g/cm³ (at 25 °C, solid)
• State at Standard Temperature and Pressure (STP): Solid
• Color: Silvery-white, lustrous (metallic appearance)
• Melting Point: 630.63 °C
• Boiling Point: 1587 °C
• Crystallography: Rhombohedral crystal structure.
• Electrical Conductivity: A poor conductor of heat and electricity compared to metals, but better than non-metals (characteristic of a metalloid).