Lithium and Alkali Metal Halides

Alkali Metal Halides

• The correct order of lattice energy is: Fluoride > Chloride > Bromide > Iodide
• Lattice energy of the same metal reduces when the halogen's electronegativity lowers
• Lithium halides exhibit aberrant behavior due to their covalent character, whereas sodium and other halides are ionic in nature
• Melting points of halides decline as we travel down the group from sodium to cesium
• NaCl > KCl > RbCl > CsCl

Solubility of Halides of Alkali Metals

• Alkali metal halides have a range of solubilities
• Solubility of alkali metal fluorides in water gradually increases from lithium to caesium
• Lithium chloride has a far better solubility in water than sodium chloride when it comes to chlorides
• Solubility in water increases steadily from sodium chloride to cesium chloride as the lattice energy of the crystals decreases

Properties of Alkali Metal Halides

• In the fused condition, they are good conductors of electricity
• They are made up of ionic crystals
• Lithium halides have a partially covalent character due to the polarising power of lithium ions
• Lattice energy and polarising power are responsible for the structure and stability (solubility) of alkali metal halides

Lattice Energy

• Lattice energy is the energy produced during the production of a crystal lattice from gaseous cations and anions
• It is also the energy necessary to split one mole of a solid ionic compound into its gaseous ions

Properties of Sodium Oxide

• It combines with carbon dioxide to produce sodium carbonate and oxygen
• It is an oxidising agent and oxidises charcoal, CO, NH3, SO2
• It contains peroxide ion

Uses of Sodium Oxide

• For preparing H2O2, O2
• Oxygenating the air in submarines
• Oxidising agent in the laboratory

Properties of Potassium Oxides

• K2O is a white powder
• K2O2 is a white powder
• K2O3 is a red powder
• KO2 is a bright yellow powder
• KO3 is a reddish-brown needles

Properties of Magnesium Oxide

• It is a white powder
• Melting point of magnesium oxide is 2850 degree Celsius
• It imparts alkaline reaction and it is very slightly soluble in water

Properties of Calcium Oxide

• It is a white amorphous powder having a melting point of 2570 degree Celsius
• When heated in an oxygen-hydrogen flame, it produces strong light (lime light)
• It is a basic oxide that reacts with acidic oxides, such as sulphur dioxide
• On combination with water, it produces slaked lime

Hydroxides

Sodium Hydroxides

• Preparation: Electrolysis of Brine and Caustication of Na2CO3 (Gossage's method)
• Properties:
  • Crystalline white solid that's highly corrosive and deliquescent
  • Resistant to heat
  • Aqueous solution has an alkaline pH and feels soapy to the touch
  • FeCl3 + 3NaOH → Fe(OH)3 ↓ +3NaCl
  • NH4Cl + NaOH → NaCl + NH3 ↑ +H2O
  • ZnCl2 + 2NaOH → Zn(OH)2 ↓ +2NaCl

Potassium Hydroxide

• Preparation: Electrolysis of aqueous solution of potassium chloride
• Properties:
  • Stronger base compared to sodium hydroxide
  • More soluble in water as compared to sodium hydroxide
  • Highly soluble in alcohol

Understand the properties of metal halides, including lattice energy, electronegativity, and melting points. Compare lithium halides to sodium and cesium halides in Class XI Chemistry.