Lecture Notes on Valence Electrons and Periodic Table

Valence Electrons and Bohr Model Review

• Bohr Model:
  • First energy shell holds 2 electrons
  • Second and third shells hold 8 electrons each
  • Beyond the fourth shell, it's inconsistent and can hold more than eight
• Example (Lithium):
  • Lithium has 3 electrons
  • First shell: 2 electrons, Second shell: 1 electron
  • Valence electron = 1 (outer shell electron)
• Example (Nitrogen):
  • Nitrogen has 7 electrons
  • First shell: 2 electrons, Second shell: 5 electrons
  • Valence electrons = 5 (outer shell)

Valence vs. Valency

• Valence Electrons: Electrons in the outermost shell.
• Valency: Number of electrons needed to complete an outer shell.
• Examples:
  • Lithium: Valence = 1, Valency = 7 (missing to complete 8)
  • Nitrogen: Valence = 5, Valency = 3 (needs 3 more to complete 8)

Periodic Table Structure

• Periods: Rows (7 periods)
• Groups: Columns (18 groups)
• Special Rows (Lanthanides and Actinides):
  • Rows 6 and 7, continuation of main table
• Elements after 95: Synthetic, man-made

Metals vs. Non-metals

• Metals:
  • Shiny, smooth, conductive
  • Typically cations, give away electrons
  • Ductile and malleable
  • Solid at room temperature (except Mercury)
• Non-metals:
  • Typically anions, often gases
  • Brittle when solid, insulators
  • Found on the right of the periodic table

Metalloids

• Properties of both metals and non-metals
• Border the staircase on the periodic table

Types of Elements

• Alkali Metals (Group 1):
  • Extremely reactive, not found alone naturally
  • React with water, have 1 valence electron
• Alkaline Earth Metals (Group 2):
  • Reactive, but less so than Group 1
  • Found in Earth's crust
• Transition Metals (Groups 3-12):
  • Reactivity varies
  • Includes industrial and precious metals
• Post-Transition Metals: Follow the transition metals
• Halogens (Group 17):
  • Extremely reactive, especially Fluorine
  • Diatomic molecules (e.g., F2, Cl2)
• Noble Gases (Group 18):
  • Inert, non-reactive due to full outer shell
  • Odorless, colorless, and used in lighting

Key Concepts

• Popular elements (Noble Gases): All elements strive to be like noble gases (full outer shell)
• Reactivity: Elements react to achieve a full outer shell, similar to noble gases
• Bonding:
  • Alkali metals often bond with halogens to form salts (e.g., NaCl)
  • Valence number indicates potential bonding capacity

Make sure to draw the periodic table outline and mark the relevant sections as described, using a key for clarity.