Lecture Notes: Alkali Metals

Introduction

• Alkali metals are located in the first column of the periodic table.
• Common elements include: Lithium, Sodium, Potassium, Rubidium, Cesium, and Francium.
• Hydrogen, although in the same group, is a non-metal.

Properties of Alkali Metals

• Conductivity: Conduct heat and electricity.
• Softness: Very soft, can be cut with a knife.
• Density: Low; e.g., Lithium is less dense than water.
• Melting Points: Low compared to other metals; e.g., Cesium melts at ~29°C.
• Atomic Radius: Large atomic radii, increases towards the left of the periodic table.
• Ionization Energy: Low ionization energy.
• Electronegativity: Low; strong reducing agents.
• Reactivity: Highly reactive, especially in water, forming hydrogen gas and hydroxides.

Trends in Group 1 (Alkali Metals)

• Reactivity: Increases down the group (Francium > Cesium > Rubidium).
• Melting and Boiling Points: Decrease down the group.
• Density: Increases down the group.
• Ionization Energy (IE1): Decreases down the group.
• Electronegativity: Decreases down the group.
• Atomic and Ionic Radius: Increase down the group.

Chemical Reactions

• Water Reaction: Alkali metals react with water to form hydroxides and hydrogen gas.
  • Sodium: 2Na + 2H₂O → 2NaOH + H₂↑
  • Lithium: Reacts similarly to sodium.
• Chlorine Reaction: Produces metal chlorides, e.g., Na + Cl₂ → 2NaCl.
• Oxygen Reaction:
  • Lithium (excess O₂): 4Li + O₂ → 2Li₂O.
  • Sodium (limited O₂): 4Na + O₂ → 2Na₂O; (excess O₂): 2Na + O₂ → Na₂O₂ (sodium peroxide).
  • Potassium: Produces superoxide (KO₂).

Reactivity Explanation

• Comparison (Lithium vs. Cesium):
  • Cesium: More reactive due to larger atomic size and lower melting point.
  • Surface Area Effect: When melted, alkali metals react faster due to increased surface area.
• Standard Reduction Potentials:
  • Lithium: -3.05 volts, stronger reducing agent.
  • Cesium: -3.02 volts, but reacts faster due to physical properties.

Key Takeaways

• Reactivity and other properties of alkali metals are determined by their position in the periodic table.
• Lower melting points lead to higher reactivity due to increased surface area in the molten state.
• Alkali metals are strong reducing agents and highly reactive especially with water and oxygen.