Tin (Sn) - Atomic Structure and Properties

Atomic Model Details

Tin (Sn) is a chemical element with atomic number 50.

• Atomic Number (Z): 50
  • Number of Protons: 50
  • Number of Electrons: 50
• Mass Number (A): The most stable and abundant isotope is Tin-120. The weighted average atomic mass is approximately 118.71 u.
  • Number of Neutrons: For Tin-120, 120 - 50 = 70 neutrons. Common isotopes range from 62 to 74 neutrons.
• Atomic Size:
  • Covalent Radius: ~145 pm
  • Van der Waals Radius: ~217 pm

Electronic Configuration & Shell Diagram

The electronic configuration describes the distribution of electrons in atomic orbitals.

• Full Electronic Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p²
• Condensed Electronic Configuration (Noble Gas Notation): [Kr] 4d¹⁰ 5s² 5p²

Shell Diagram Representation (Electron Distribution by Shell):

• 1st Shell (K): 2 electrons
• 2nd Shell (L): 8 electrons
• 3rd Shell (M): 18 electrons
• 4th Shell (N): 18 electrons
• 5th Shell (O): 4 electrons (Valence electrons)

This distribution can be written as (2, 8, 18, 18, 4). The presence of four valence electrons (5s² 5p²) is characteristic of Group 14 elements, leading to typical oxidation states of +2 and +4.

Periodic Trends

Ionization Enthalpy (IE)

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

• First Ionization Enthalpy: ~708.6 kJ/mol
• Second Ionization Enthalpy: ~1411.8 kJ/mol
• Trend: Down Group 14, the first ionization enthalpy generally decreases from Carbon to Germanium. However, due to the presence of completely filled d and f orbitals in elements like Tin (and Lead), the shielding effect is poorer, leading to a slight increase or irregular trend for the heavier elements compared to the expected continuous decrease. Tin’s first IE is lower than Germanium’s but shows the general decreasing trend down the group.

Electronegativity

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

• Pauling Scale Electronegativity: ~1.96
• Trend: Electronegativity generally decreases down a group due to increasing atomic size and shielding effect, making the valence electrons further from the nucleus and less attracted to it. Tin follows this general trend, being less electronegative than Carbon, Silicon, and Germanium.

Electron Gain Enthalpy (EGE)

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

• Electron Gain Enthalpy: ~-107 kJ/mol
• Trend: Down Group 14, electron gain enthalpy generally becomes less negative (less exothermic), indicating a decreasing tendency to accept an extra electron. This is due to increasing atomic size and more diffuse electron clouds. Tin’s electron gain enthalpy is less negative than its lighter congeners.

Atomic Radius

Atomic radius is a measure of the size of an atom.

• Covalent Radius: ~145 pm
• Trend: Atomic radius generally increases down a group due to the addition of new principal energy shells, which are further away from the nucleus and shielded by inner electrons. Tin has a larger atomic radius than Silicon and Germanium, consistent with this trend.

Key Physical Properties

• Density (at 20°C):
  • White Tin (α-Sn, cubic structure): 5.75 g/cm³
  • White Tin (β-Sn, tetragonal structure): 7.26 g/cm³
• State at Standard Temperature and Pressure (STP): Solid
• Color: Silvery-white, lustrous metal when freshly cut; tarnishes to a dull grey in air. It has two main allotropic forms: grey tin (α-tin), a semiconductor, and white tin (β-tin), a metal.
• Melting Point: 231.9 °C
• Boiling Point: 2602 °C