Gallium (Ga): Atomic Structure and Properties

Gallium (Ga): Atomic Structure and Chemical Properties

Gallium (Ga) is a chemical element with atomic number 31. It belongs to Group 13 (Boron family) and Period 4 of the periodic table.

Atomic Model Details

• Atomic Symbol: Ga
• Atomic Number (Z): 31
  • Indicates 31 protons in the nucleus.
  • In a neutral atom, there are 31 electrons.
• Atomic Mass: 69.723 u (or g/mol)
• Neutrons: The most common isotope, Gallium-69 ($^{69}\text{Ga}$), has 38 neutrons (69 - 31). Gallium-71 ($^{71}\text{Ga}$) has 40 neutrons. The atomic mass is an average of these isotopes.
• Atomic Size/Radius:
  • Covalent Radius: 122 pm
  • Van der Waals Radius: 187 pm
  • Ionic Radius (Ga³⁺): 62 pm

Electronic Configuration & Shell Diagram

• Electronic Configuration: [Ar] 3d¹⁰ 4s² 4p¹
  • The presence of fully filled 3d orbitals (3d¹⁰) significantly influences its properties compared to Aluminium.
• Shell Diagram Representation:
  • 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): 3 electrons (4s² 4p¹) - These are the valence electrons.

Periodic Trends

Gallium exhibits some deviations from expected periodic trends due to the d-block contraction (poor shielding by 3d electrons) and increased effective nuclear charge (Zeff).

• Ionization Enthalpy (IE):
  • First Ionization Enthalpy (IE₁): 578.8 kJ/mol
  • Second Ionization Enthalpy (IE₂): 1979.3 kJ/mol
  • Third Ionization Enthalpy (IE₃): 2963 kJ/mol
  • Trend: Gallium’s first ionization enthalpy is slightly higher than that of Aluminium (577.5 kJ/mol). This is unexpected, as IE usually decreases down a group. This anomaly is attributed to the presence of 3d¹⁰ electrons in Gallium, which provide poor shielding, leading to a stronger effective nuclear charge and thus a tighter hold on the valence electrons.
• Electronegativity (Pauling scale): 1.81
  • Trend: Gallium has a higher electronegativity than Aluminium (1.61). Similar to ionization enthalpy, the increased effective nuclear charge due to the poor shielding of 3d electrons results in a greater attraction for electrons.
• Electron Gain Enthalpy (EGE): -29 kJ/mol
  • Trend: It has a small negative electron gain enthalpy, indicating a slight tendency to accept an electron, but it typically forms positive ions.
• Atomic Radius: 122 pm (covalent radius)
  • Trend: Gallium’s atomic radius (122 pm) is smaller than that of Aluminium (143 pm). This is a direct consequence of the d-block contraction, where the 3d electrons’ poor shielding causes the outer shell electrons to be pulled closer to the nucleus.

Key Physical Properties

• Density:
  • Solid (at 20°C): 5.91 g/cm³
  • Liquid (at 29.76°C): 6.095 g/cm³ (Unusual property: liquid Gallium is denser than solid Gallium, similar to water)
• State at Room Temperature (25°C): Solid
• Color: Silvery-white (solid); Silvery (liquid)
• Melting Point: 29.76 °C (Remarkably low for a metal, allows it to melt in the palm of one’s hand.)
• Boiling Point: 2204 °C (Exhibits a very wide liquid range, making it useful in high-temperature thermometry.)
• Crystal Structure: Orthorhombic
• Electrical Conductivity: Good conductor of electricity.