Lecture on Electrons and the Periodic Table

Structure of an Atom

• An atom consists of:
  • Nucleus: Contains protons and neutrons.
  • Electrons: Occupy spaces around the nucleus known as energy levels or shells.
  • Electrons can be thought of as occupying parking spots within these shells.

Energy Levels (Shells)

• Electrons are organized into energy levels/shells around the nucleus.
• First energy level: Can hold up to 2 electrons.
• Second energy level: Can hold up to 8 electrons.
• Third energy level: Can hold up to 8 electrons.
• Although not the most accurate representation, this model helps in understanding the basics.

Periodic Table and Electrons

• We use a simplified version of the periodic table, focusing on certain columns.
• Valence Electrons: Electrons in the outermost shell, crucial for chemical properties.

Example Elements:

Hydrogen

• Has 1 proton (atomic number 1).
• Neutral hydrogen atom: 1 electron.
• Diagram: 1 electron in the first energy level.

Lithium

• 3 protons (atomic number 3), 3 electrons in a neutral atom.
• First energy level filled (2 electrons), 1 electron in the second energy level.

Sodium

• 11 protons (atomic number 11), 11 electrons in a neutral atom.
• First energy level (2 electrons), second level (8 electrons), third level begins with 1 electron.

Pattern of Valence Electrons

• Elements in the same group have the same number of valence electrons:
  • Group 1 (e.g., Hydrogen, Lithium, Sodium): 1 valence electron.
  • Group 2 (e.g., Beryllium, Magnesium): 2 valence electrons.
  • Group 13 (e.g., Boron, Aluminum): 3 valence electrons.
  • Group 14 (e.g., Carbon, Silicon): 4 valence electrons.
  • Group 15 (e.g., Nitrogen, Phosphorus): 5 valence electrons.
  • Group 16 (e.g., Oxygen, Sulfur): 6 valence electrons.
  • Group 17 (e.g., Fluorine, Chlorine): 7 valence electrons.
  • Group 18 (e.g., Helium, Neon, Argon): Typically 8 valence electrons, except Helium which has 2.

Electron Dot Diagrams (Lewis Diagrams)

• Used to represent valence electrons:
  • Group 1: One dot.
  • Group 2: Two dots.
  • Group 13: Three dots.
  • Group 14: Four dots.
  • Group 15: Five dots.
  • Group 16: Six dots.
  • Group 17: Seven dots.
  • Group 18: Eight dots (or two for Helium).

Summary

• The number of valence electrons can be determined by an element's position in the periodic table.
• Understanding valence electrons is crucial for understanding chemical bonding and reactions.