Bismuth (Bi) - Atomic Structure & Chemical Properties

Atomic Model Details

Bismuth (Bi) is a p-block element located in Group 15 and Period 6 of the periodic table. It is the heaviest stable naturally occurring element.

Fundamental Particles

• Atomic Number (Z): 83
  • Indicates 83 protons in the nucleus.
  • In a neutral atom, there are 83 electrons.
• Mass Number (A): Approximately 209 (for the most stable isotope, Bismuth-209, often denoted as ²⁰⁹Bi).
• Neutrons: A - Z = 209 - 83 = 126 neutrons.

Atomic Size

• Metallic Radius: Approximately 163 pm (picometers).
• Covalent Radius: Approximately 146 pm.

Electronic Configuration & Shell Diagram

Electronic Configuration

The ground state electronic configuration of Bismuth is: [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p³

This configuration indicates:

• [Xe]: The configuration of Xenon, representing the core electrons.
• 4f¹⁴: A completely filled 4f subshell, contributing to the lanthanide contraction effect.
• 5d¹⁰: A completely filled 5d subshell.
• 6s²: A completely filled 6s subshell.
• 6p³: A half-filled 6p subshell, indicating its position in Group 15 (pnictogens).

Shell-wise Electron Distribution

The electrons are distributed in the principal energy shells as follows:

• K-shell (n=1): 2 electrons
• L-shell (n=2): 8 electrons
• M-shell (n=3): 18 electrons
• N-shell (n=4): 32 electrons
• O-shell (n=5): 18 electrons
• P-shell (n=6): 5 valence electrons (2 in 6s, 3 in 6p)

Periodic Trends

Ionization Enthalpy (First)

• Value: Approximately 703 kJ/mol.
• Trend: As a Group 15 element, its first ionization enthalpy is relatively high compared to Group 1 and 2 elements due to a stable half-filled p-subshell. Down the group, ionization enthalpy generally decreases, but for Bismuth, the presence of fully filled 4f and 5d orbitals leads to a slightly higher value than expected due to poor shielding (lanthanide contraction and d-block contraction) increasing the effective nuclear charge.

Electronegativity (Pauling Scale)

• Value: Approximately 2.02.
• Trend: Electronegativity generally decreases down a group due to increasing atomic size and shielding. Bismuth, being at the bottom of Group 15, has a relatively low electronegativity compared to its lighter congeners, indicating its metallic character.

Electron Gain Enthalpy

• Value: Approximately -91 kJ/mol.
• Trend: For metallic elements like Bismuth, the electron gain enthalpy is usually less negative or even positive. Bismuth has a slight tendency to accept an electron, but it is not a strong electron acceptor, reflecting its metallic nature.

Atomic Radius (Metallic Radius)

• Value: Approximately 163 pm.
• Trend: Atomic radius generally increases down a group due to the addition of new electron shells. However, due to the lanthanide contraction and the presence of 5d electrons (d-block contraction), the increase in atomic radius across the 6th period elements after the d and f blocks is not as pronounced as might be expected, but it is larger than lighter Group 15 elements.

Key Physical Properties

• Density: 9.78 g/cm³ (at 20 °C).
• State at STP (Standard Temperature and Pressure): Solid.
• Color: Silvery-pinkish-white, often exhibiting an iridescent (rainbow-like) tarnish layer of bismuth oxide when exposed to air.
• Melting Point: 271.5 °C.
• Boiling Point: 1564 °C.
• Classification: Post-transition metal, often considered a metalloid due to some similarities to non-metals. It is diamagnetic.