Beryllium (Be): Atomic Structure and Chemical Properties

Atomic Structure

Beryllium (Be) is the first element of Group 2 (Alkaline Earth Metals) in the periodic table.

Atomic Model Details

• Atomic Number (Z): 4
• Number of Protons: 4
• Number of Electrons: 4
• Common Isotope (⁹Be):
  • Mass Number (A): 9
  • Number of Neutrons: A - Z = 9 - 4 = 5
• Atomic Size (Covalent Radius): Approximately 112 picometers (pm).

Electronic Configuration and Shell Diagram

• Electronic Configuration: 1s² 2s²
• Shell Diagram Representation:
  • K-shell: Contains 2 electrons.
  • L-shell (Valence Shell): Contains 2 electrons.
  • This configuration indicates that Beryllium has two valence electrons in its outermost shell (2s subshell), which it tends to lose to form a +2 ion (Be²⁺).

Periodic Trends

Ionization Enthalpy (IE)

• First Ionization Enthalpy (ΔiH₁): 899.5 kJ/mol
• Second Ionization Enthalpy (ΔiH₂): 1757.1 kJ/mol
• Trend: Beryllium has a relatively high first ionization enthalpy compared to other Group 2 elements due to its small atomic size and high effective nuclear charge. It is also higher than that of Lithium (Li) in the same period because of the fully filled 2s orbital and increased nuclear charge.

Electronegativity

• Pauling Scale Electronegativity: 1.57
• Trend: Beryllium is one of the most electronegative elements among the alkaline earth metals, consistent with its small size.

Electron Gain Enthalpy (EGE)

• Electron Gain Enthalpy (ΔegH): +240 kJ/mol (endothermic)
• Trend: Beryllium has a positive electron gain enthalpy. This indicates that energy must be supplied to add an electron to a gaseous beryllium atom, as its 2s orbital is completely filled, making it energetically unfavorable to accept an additional electron into a higher energy orbital.

Atomic Radius

• Covalent Radius: 112 pm
• Metallic Radius: 112 pm
• Trend: Beryllium has the smallest atomic radius among the alkaline earth metals due to the highest effective nuclear charge for its period and the absence of inner d-orbitals.

Key Physical Properties

• Density: 1.85 g/cm³ (at 20 °C)
• State at Standard Temperature and Pressure (STP): Solid
• Color: Steel gray
• Melting Point (MP): 1287 °C
• Boiling Point (BP): 2471 °C