Calculating Valence Electrons and Core Electrons

Introduction

• Understanding valence electrons is crucial for grasping chemical reactions and bonding.
• This lecture discusses how to calculate and understand valence electrons using examples of different atoms.

Nitrogen Atom

• Atomic Number: 7
• Average Atomic Mass: 14.01
• Protons/Electrons: 7
• Bohr Model:
  • 1st energy level: 2 electrons (max capacity)
  • 2nd energy level: 5 electrons
• Valence Electrons: 5 (outermost energy level)
• Core Electrons: 2
• Note: Atoms are electrically neutral. In ions, protons and electrons differ.

Aluminum Atom

• Atomic Number: 13
• Average Atomic Mass: 26.98
• Electrons Distribution:
  • 1st energy level: 2 electrons
  • 2nd energy level: 8 electrons
  • 3rd energy level: 3 electrons
• Valence Electrons: 3 (highest energy level)
• Core Electrons: 10 (2 in the first shell, 8 in the second shell)
• Electron Configuration: 1s² 2s² 2p⁶ 3s² 3p¹
  • Valence electrons in highest energy level: 3
  • Core electrons: 10

Chlorine Atom

• Atomic Number: 17
• Electron Configuration: 1s² 2s² 2p⁶ 3s² 3p⁵
  • Valence electrons: 7 (2+5 in highest energy level)
  • Core electrons: 10

Using The Periodic Table

• Group numbers indicate valence electrons:
  • Group 1: 1 valence electron (e.g., hydrogen, lithium)
  • Group 2: 2 valence electrons (alkaline earth metals)
  • Group 13 (3A): 3 valence electrons (includes boron, aluminum)
  • Group 14 (4A): 4 valence electrons (carbon, silicon)
  • Group 15 (5A): 5 valence electrons (nitrogen, phosphorus)
  • Group 16 (6A): 6 valence electrons (chalcogens like oxygen)
  • Group 17 (7A): 7 valence electrons (halogens like fluorine, chlorine)
  • Group 18: Noble gases, typically 8 valence electrons (except helium with 2)

Example: Iodine Atom

• Atomic Number: 53
• Valence Electrons: 7 (Group 7A)
• Calculating Core Electrons:
  • Total electrons = 53 (atomic number)
  • Core electrons = Total electrons - Valence electrons = 53 - 7 = 46

Efficient Calculation

• For large atoms, use:
  • Total Electrons = Core Electrons + Valence Electrons
  • Subtract group number from atomic number for core electron count.

Conclusion

• Understand electron distribution across energy levels to identify valence and core electrons.
• Utilize periodic table groups for quick identification of valence electrons.