Properties of Elements - Lecture Notes

Overview

• Discussion on chemical and physical properties of elements
• Relation of properties to positions on the periodic table

Classification of Elements

1. Metals

   • Atoms donate outer electrons to form a metallic bond
   • Found on the left and bottom of the periodic table
   • Low electronegativity and ionization energy

2. Non-metals

   • Gain full outer shells by forming covalent bonds
   • Found at the top and right of the periodic table
   • High electronegativity and ionization energy

3. Metalloids

   • Properties between metals and non-metals
   • Found in a zigzag pattern from Boron to Polonium
   • Shiny like metals, chemically resemble non-metals
   • Act as semiconductors

Types of Bonding

• Ionic Bonding

  • Occurs with a large electronegativity difference (ΔX > 1.8)

• Covalent Bonding

  • Occurs with a small electronegativity difference (ΔX < 1.8)
  • Polar covalent bonds if 0.5 < ΔX < 1.8

Group Trends

Group 1: Alkali Metals

• Characteristics:

  • Soft metals, low melting points
  • Form +1 ions
  • Atomic radius increases down the group
  • Ionization energy decreases making them more reactive

• Physical Properties:

  • Soft, low melting points
  • Weak metallic bonding due to larger atom sizes

Group 17: Halogens

• Characteristics:

  • Non-metals, low melting and boiling points
  • Form diatomic molecules
  • Atomic radius increases, electronegativity decreases down the group

• Physical Properties:

  • Florine and chlorine are gases, bromine is a liquid, iodine is a solid
  • Dispersion forces increase with size

Period Trends - Period 3

• Metallic to Non-metallic Transition

  • Left: Metals (sodium to aluminum), Right: Non-metals (phosphorus to argon)
  • Middle: Silicon as a metalloid

• Melting and Boiling Points

  • Metals have higher melting points due to metallic bonding
  • Silicon has a high melting point due to its covalent lattice structure
  • Non-metals have lower melting points influenced by weak dispersion forces

Oxides Across Periods 2 and 3

• Metal Oxides

  • Typically basic, form hydroxides in water
  • Aluminum oxide is amphoteric (reacts with both acids and bases)

• Non-metal Oxides

  • Typically acidic, form acids in water
  • Strength and acidity increase across a period

Recap

• Metals, non-metals, and metalloids' positions on the periodic table
• Ionic vs. covalent bonding based on electronegativity
• Group 1 and 17 exemplify trends of metals and non-metals respectively
• Period 3 demonstrates changing properties across a period
• Oxide character transitions from basic to acidic across a period