Francium is highly radioactive, its longest-lived isotope Fr-223 (half-life of only 21 minutes).
Sodium, potassium, magnesium and calcium ions are found in biological fluids.
Maintenance of ion balance and nerve impulse conduction
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Density: Li < K < Na < Rb < Cs
Reactivity Li < Na < K < Rb < Cs
I.P. Li > Na > K > Rb > Cs
Melting point Li > Na > K > Rb > Cs
Boiling point Li > Na > K > Rb > Cs
Electropositive character Li < Na < K < Rb < Cs
Photoelectric effect: Except Li (High I.P.) all elements show this effect, Cs used in solar cell.
Reactivity towards air:
Because of their high reactivity towards air and water, alkali metals are normally kept in kerosene oil.
Reactivity towards water:
The alkali metals react with water to form hydroxide and dihydrogen.
Li do not react with water due to its small size and very high hydration energy.
Reactivity towards halogens:
The low solubility of LiF in water is due to its high lattice enthalpy
The low solubility of CsI is due to smaller hydration enthalpy of its two ions
The amount of energy released when an ionic solid is formed from its gaseous ionic constituents.
Lattice enthalpy is a measure of the strength of the forces between the ions in an ionic solid. The greater the lattice enthalpy, the stronger the forces.
The melting and boiling points always follow the trend:
fluoride > chloride > bromide > iodide
The hydration enthalpy is the enthalpy change when 1 mole of gaseous ions dissolve in water to form hydrated ion. Hydration enthalpies are always negative.
Hydration Enthalpy: The hydration enthalpies of alkali metal ions decrease with increase in ionic sizes.
Li⁺ > Na⁺ > K⁺ > Rb⁺ > Cs⁺
Salts of Oxo-Acids
Their carbonates (M₂CO₃) and in most cases the hydrogen carbonates (MHCO₃) also are highly stable to heat.
As the electropositive character increases down the group, the stability of the carbonates and hydrogen carbonates increases.
Cs₂CO₃ > Rb₂CO₃ > K₂CO₃ > Na₂CO₃ > Li₂CO₃
Reducing nature and Electrode Potential
The alkali metals are strong reducing agents, readily lose electrons
In Gas phase: I.P determine the tendency to lose electrons
Li < Na < K < Rb < Cs
In aqueous phase: Electrode Potential determine the tendency to lose electrons
Li > K > Rb > Cs > Na
Solutions in liquid ammonia: The alkali metals dissolve in liquid ammonia giving deep blue solutions which are conducting in nature.
Sodium Carbonate (Washing Soda) Na₂CO₃.10H₂O
Prepared by: Solvay Process
Solvay process cannot be extended to the manufacture of potassium carbonate because potassium hydrogen carbonate is too soluble to be precipitated by the addition of ammonium hydrogen carbonate to a saturated solution of potassium chloride.
2NH3 + H2O + CO2 → (NH4)2CO3
(NH4)2CO3 + H2O + CO2 → 2NH4HCO3
NH4HCO3 + NaCl → NH4Cl + NaHCO3
2NaHCO3 → Na2CO3 + CO2 + H2O
2NH4Cl + Ca(OH)2 → 2NH3 + CaCl2 + H2O