Introduction of alkali metals (Group IA)

Introduction of alkali metals (Group IA)

Group 1A:  The Alkali Metals

Configuration of alkali metals

The elements of Group 1, the Alkali metals, are:

Element	Symbol	Electron configuration
Lithium	3Li	[He]2s1
Sodium	11Na	[Ne]3s1
Potassium	19K	[Ar]4s1
Rubidium	37Rb	[Kr]5s1
Cesium	55Cs	[Xe]6s1
Francium	87Fr	[Rn]7s1

 

Because the alkali metals are strong reducing agents, electrolysis is the only way for extraction of them from their compounds.

Alkali metals properties

    The alkali elements characterized by:

a.      Bright silvery luster.

b.     They are good conductors of electricity and heat.

c.      They are the softest metals

d.     They possess the lowest melting temperatures.

e.      As descending the group the melting points, boiling points, and hardness of metals decrease.

f.       These elements have the +1 oxidation state only. The second ionization energy is so large that the +2 oxidation state is unstable and is never observed.

 

Standard Molar Enthalpy of hydration △H^o_hyd:

Enthalpy of Hydration (Hydration energy) △H^o_hyd: It is the energy evolved when ions are hydrated by water.

 

The equation for the electrostatic energy of an ion of radius r and charge q is

                                   

                                 D = dielectric constant of the solvent.

 

Thus we can obtain △H^o_hyd for individual cation as follow:

                                                 

   

 where Z is the charge number of the ion and  the effective radius of the ion in water in angstroms.

 

Alkali Metal Oxides:

-         Lithium reacts with oxygen to give monoxide Li₂O.

-         Sodium reacts with oxygen to give sodium peroxide Na₂O₂.

-         The other alkali metals react with oxygen to form superoxides MO₂.

-         The simple monoxides of all the alkali metals can be prepared by reduction of their nitrates as follow:

 

 

-         All the oxides are strong bases and dissolve readily in water by reactions of the type                          

 

-         The alkali metal hydroxides like NaOH are ionic compounds and soluble in water and are strong bases.

 

The Alkali Metal Halides:

o   These compounds are stable crystalline substances of high melting and boiling temperature. the reason for the high stability of the alkali halides is the high lattice energy (crystallization energy).

 

o  Enthalpy of hydration of Alkali Metal Halides

The hydration of the gaseous ions and the formation of solutions from crystals can be calculated from the relation:

The more negative the value of △H^o_sol  the more soluble is the halide for example

 

The Binding of Alkali Metal Ions (Binding in alkali metals):

 

§  In organic cyclic polyethers the oxygens are held at a fixed distance for interaction (fixed geometry) with K⁺ or Na⁺. Cyclic polyethers should be bind Na⁺ ions differently than K⁺ ions and therefore K⁺ and Na⁺ can be differentiated.

 

§  The Figure shows the structure of these polyethers.

 

How polyether works:

§  The metal ions bind to these polyethers by filling the center cavity in the ring and attempting to interact with as many oxygens as possible.