Unit 10: The s-Block Elements

Overview

• The s-block elements include groups 1 and 2 of the periodic table.
• Group 1: Alkali metals (Li, Na, K, Rb, Cs, Fr)
  • Highly reactive, form hydroxides that are alkaline.
• Group 2: Alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra)
  • Form oxides and hydroxides that are alkaline.

Objectives

• Understand characteristics of alkali and alkaline earth metals.
• Learn about industrially important sodium and calcium compounds.
• Recognize the biological significance of Na, K, Mg, and Ca.

Characteristics of Alkali Metals (Group 1)

• Electronic Configuration: ns1 (one valence electron)
• Properties:
  • Large atomic and ionic radii, low ionization enthalpies.
  • Soft, low-density, and low-melting metals.
  • High reactivity, especially with air and water.
• Trends:
  • Increase in size and decrease in ionization enthalpy down the group.
  • Reactivity increases from Li to Cs.
• Chemical Reactions:
  • React with air to form oxides; with water to form hydroxides and H2.
  • Form ionic halides with halogens; lithium halides have more covalent character.

Characteristics of Alkaline Earth Metals (Group 2)

• Electronic Configuration: ns2 (two valence electrons)
• Properties:
  • Smaller atomic and ionic radii compared to alkali metals due to higher nuclear charge.
  • Less reactive than alkali metals, but reactivity increases down the group.
  • Forms ionic compounds, higher melting and boiling points than group 1 metals.
• Chemical Reactions:
  • React with oxygen, forming monoxides.
  • Form halides with halogens; Be halides are more covalent.

Notable Compounds

Alkali Metals

• Sodium Compounds:
  • Sodium Carbonate: Made via Solvay Process.
  • Sodium Hydroxide: Made by electrolysis (Castner-Kellner cell).
  • Sodium Chloride: Obtained from sea water.

Alkaline Earth Metals

• Calcium Compounds:
  • Calcium Oxide: Manufactured by heating CaCO3.
  • Calcium Hydroxide: Used in mortar and as a disinfectant.
  • Calcium Carbonate: Used as a building material.
  • Cement: Made from limestone and clay.

Biological Importance

• Sodium and Potassium:
  • Key in nerve impulse transmission and cell function.
• Magnesium and Calcium:
  • Mg: Cofactor for enzymes; in chlorophyll.
  • Ca: Vital for bone health and cellular processes.

Anomalous Properties

• Lithium:
  • Smaller size, high polarizing power, increased covalency.
  • Shows diagonal relationship with magnesium.
• Beryllium:
  • Smallest in group 2, behaves similarly to aluminum.

Exercises

• Compare physical and chemical properties of alkali and alkaline earth metals.
• Discuss reactivity trends, solubility, and stability of their compounds.
• Understand applications in industry and biological systems.