Lecture Notes: Valence Electrons and the Periodic Table

Valence Electrons

• Bohr Model Review

  • Electrons are held in shells.
  • 1st shell: 2 electrons
  • 2nd and 3rd shells: 8 electrons each
  • After 4th shell: More complex, exceptions exist.
  • Example (Lithium):
    • 1st shell: 2 electrons
    • 2nd shell: 1 electron (valence electron)

• Valence Electrons Definition

  • Electrons on the outermost shell.
  • Example (Nitrogen): 5 valence electrons.

Valence vs. Valence Electrons

• Valence: Number of missing electrons to complete the outer shell.
  • Example (Lithium): Valence is 7.
  • Example (Nitrogen): Valence is 3.
• Valence Electrons: Electrons in the outer shell.

Periodic Table Structure

• Rows (Periods)
  • 7 periods
• Columns (Groups)
  • 18 groups
• Special Rows: Rows at the bottom are continuations of periods 6 and 7 (lanthanides and actinides).
• Synthetic Elements: After element 95, elements are man-made.

Metals vs. Non-Metals

• Metals
  • Shiny, smooth, conductors, typically cations.
  • Ductile, malleable, mostly solid at room temperature.
• Non-Metals
  • Usually anions, many are gases.
  • Brittle solids, insulators.
  • Located on the right side of the periodic table.
• Metalloids: Properties of both metals and non-metals, border the staircase on the periodic table.

Types of Metals and Non-Metals

• Alkali Metals (Group 1)
  • Extremely reactive, not including hydrogen.
  • One valence electron, eager to bond.
• Alkaline Earth Metals (Group 2)
  • Reactive, but less so than alkali metals.
  • Found in the Earth's crust.
• Transition Metals (Groups 3-12)
  • Reactivity varies, includes industrial and precious metals like iron, silver, gold.
• Post-Transition Metals: Includes aluminum, lead, tin, etc.
• Halogens (Group 17)
  • Extremely reactive non-metals, diatomic.
  • Example: F2 (fluoride), Cl2 (chlorine).
• Noble Gases (Group 18)
  • Inert, non-reactive gases, full outer shell (valence is zero).
  • Used in lighting due to inert nature.

Bonding and Reactivity

• Alkali Metals and Halogens: Often bond together to form salts (e.g., Sodium Chloride - table salt).
• Valence in Bonding: Determines how many electrons are needed or shared in bonds; guides reactivity and chemical behavior.
• Popular Elements: Elements strive to achieve a full outer shell like noble gases.

Key Takeaways

• Understanding the periodic table helps in predicting chemical properties and behaviors.
• Valence electrons and valence are crucial for determining how elements will react or bond with others.