Periodic Trends for Ionization Energy

General Trend Across a Period

• Increase in Ionization Energy: As we move across a period from lithium (Li) to neon (Ne), there is an increase in the ionization energy.
  • Example: Li = 520 kJ/mol to Ne = higher value.
• Reason: Increase in the effective nuclear charge (Z effective), which is calculated as:
  • Z (number of protons) - S (average number of inner electrons).

Detailed Examination of Lithium and Beryllium

• Lithium (Li):

  • Atomic number 3 (3 protons).
  • Electron configuration: 1s² 2s¹.
  • Effective nuclear charge: +3 (nuclear charge) - 2 (shielding electrons) = +1.
  • Outer electron feels a +1 charge, roughly calculated as 1.3.

• Beryllium (Be):

  • Atomic number 4 (4 protons).
  • Electron configuration: 1s² 2s².
  • Effective nuclear charge: +4 - 2 = +2.
  • Outer electron feels a +2 charge, more accurately 1.9.

Influence on Atomic Size and Ionization Energy

• Smaller Atoms: Beryllium is smaller than lithium.
• Higher Ionization Energy: More energy is required to remove an electron from beryllium than from lithium.
  • Example: Be has 900 kJ/mol compared to Li's 520 kJ/mol.

Decrease in Ionization Energy Between Beryllium and Boron

• Boron (B):
  • Electron configuration: 1s² 2s² 2p¹.
  • Ionization energy decreases to 800 kJ/mol due to the 2p electron being further from the nucleus and additional shielding by 2s electrons.

Further Trends

• Carbon to Nitrogen: Increase in ionization energy due to increased nuclear charge.
• Nitrogen to Oxygen: Slight decrease in ionization energy.
  • Electron configuration:
    • Nitrogen: 1s² 2s² 2p³.
    • Oxygen: 1s² 2s² 2p⁴.
  • Added electron in oxygen's 2p orbital experiences repulsion, making it easier to remove.

Continued Trend

• After oxygen, the ionization energy increases again from fluorine (F) to neon (Ne).
• Reason: Continued increase in effective nuclear charge.