Alkali metal.

Alkali metal.

The element such as lithium, sodium, rubidium, francium, which are placed in Group IA (1) of the periodic table are called alkali metal It general follow ns¹ electronic configuration. All the element present in this group is highly reactive metal at standard temperature and pressures, shiny soft, excellent conductor of electricity, electropositive, monovalent metal forming strongly alkaline hydroxides.It follows the general property such as atomic radius, ionisation energy, Metallic or electropositive character, hydration energy, this element readily looses their outermost electron to form cations with charge +1. The physical and chemical properties of the elements present in an alkali metal group are closely related to their electronic structure and sizes. All the elements have one loosely held valence electron in their outer shell and typically form univalent, ionic, and colourless compounds. The hydroxides and oxides are very strong bases, and the oxo salts are very stable.

Lithium the first elements in the group shows the considerable differences from the rest of the other elements in this group. In all of the elements, the first elements show a number of differences from the later elements in the group.Sodium and Potassium together make up of over 4 % by weight of the earth's crust. These compounds are very common and have been known and used from very early times.Some of the compounds are used in very large amount.Different alkali metal in this group has different application.Sodium and the potassium are the elements that are used in the biological process that is used as electrolyte rubidium and caesium is used in the atomic where other alkali metals are not in used.The alkali metal which is not essential in the biology role they have a various role in the body, both beneficial and harmful.

The solution of alkali metal in liquid ammonia.

$$NH_3(g) \overset{-34^{\circ}{c}}{\rightarrow}NH3(l)$$

$$NH3+H20\rightleftharpoons NH_4$$

In an absence of any impurities all metal ammonia without the evolution of hydrogen gas. The resulting solution is called metal-ammonia. solution.

Property of metal-ammonia solution.

Some of the properties of metal-ammonia solution are as follows

1. . Electrical conductivity.
2. Colour of the solution.
3. Stability of metal-ammonia solution.

1. Electrical conductivity.

$$M+(X+Y)NH_3(l)→M^+(NH_3)_x+e^-(NH_3)_y$$

$$M^+(NH_3)_x=Solvated\,ammonia\,cation$$

$$e^-(NH_3)_y=Solvated\,electron$$

Concentrate solution of alkali metal in liquid ammonia is a remarkable good conductor of electricity. This is due to the presence of a large number of solvated cation and the presence of the solvated electrons.

2.Solvated electron.

The electron surrounded by the polar solvent molecule under the electrostatic force of attraction between electron and solvent molecule is called solvated electron.

3.Colour of a solution.

Dilute metal-ammonia solution appears blue in colour. Blue colour of metal-ammonia solution is due to excitation of an electron from lower energy to higher energy level.The excitation of the election is accompanied by the absorption of light in the red region of the spectrum.Hence, the solution appears blue in its transmitted light [( complementary colour of red colour is blue)].

4. Stability of metal-ammonia solution.

$$M+NH_3\xrightarrow[]{pure}stable$$

$$M+NH_3\xrightarrow[]{impurities\,catalyst\,UV radiation}MNH_2+\frac{1}{2}H_2$$

In the absence of any impurities, the metal-ammonia solution is quite stable. However, if the solution is kept for a long time, or in the presence of impurities or catalyst or UV radiation. The solution decomposed to form a metal amide and H₂ gas is evolved.

The organometallic compound of the lithium : Lithium alkyls/ aryls (LiR).

Lithium has strong tendency to form covalent compounds than other alkali metals.Hence, lithium forms a large number of organometallic compounds with alkyls or aryls groups. This compound exists either as tetramer or hexamer.

Example.

[Li(CH₃)₄]

[Li(C₂H₅)₄] exists in a solid state but exists as

but exists as [Li(c2H5)₆] which dissolve in a hydrocarbon solvent.

[Li(C4H9)4] etc.are some of the examples of an organometallic compound of lithium.

The organometallic compounds are of great importance i the preparation of the other organic compounds. Some of the common examples of organometallic compounds are discussed below.

a. $$LiR+R'-X→R-R'+LiX$$

$$R-R'=alkane$$

b.$$LiR+Cl_2→R-Cl+LiCl$$

$$R-Cl= alky\, halide$$

c.$$LiR+HCON(Me)_2→RCOH+LiN(Me)_2$$

$$RCOH = aldehyde$$

d.$$2LiR+CO_2→RCOR+LiCO$$

$$RCOR= ketone$$

e.$$LiR+CO_2+H_2O→RCOOH+LiOH$$

$$RCOOH= carboxylic acid$$

Chloro alkali industry and their application.

Chloro alkali industry involves the manufacture of NaOH (caustic soda) Na₂CO₃ (soda ash/washing soda) and chlorine.All these chemical are prepared from NaCl. These three chemicals are also called 'heavy inorganic chemicals' due to these wide applications in the various field.

Application of Sodium Carbonate.Na₂CO₃

It is used in the laundry as well as softer, in the manufacture of glass caustic soda as lab-reagent, textile, petrol refining, paper making.

Application of Caustic soda. NaOH.

It is used in the manufacture of sodium metal, soap, rayon, paper, dyes, drugs, in petrol refining, as lab, reagent etc.

Application of Chlorine.

1. It is used in the manufacture of plastic such as PVC (Poly Vinyl Chloride), chloromethane, (CHCl₃) CH₂Cl₂ etc, an inorganic compound such as bleaching powder, sodium hypochlorite, (NaoCl).

2. It is used as the bleaching agent.

3. It is used as sterilising drinking water.

4. It is also used in paper production, antiseptic, medicine, textile etc.

Crown and Crypt ether.

Crown ether.

Crown ether is cyclic polyether which acts as a small multidentate ligand. In the crown ether, the oxygen atoms are separated by two CH₂ (methylene) groups and the organic part is puckered to give crown arrangement. Crown ether can bind the alkali metals ions in the centre and form complexes. In such complexes bonding between the central metal atom and the bonding between the central metal atom and the crown is largely electrostatic in nature.

Stability of metal complex with crown ether.

Stability of metal complex with crown ether depends on the size of metal ion and the size of the cavity in the ring.In order to form stable complexes, the size of metal, ion and the size of the cavity in the ring should be similar. Either too large size of the metal ion or the ring form a less stable complex. Hence, the formation of metal complexes with crown ether is high selectivity. The size of metal ion determined the size of crown ether with which forms a stable complex. That's why Li⁺ prefer to form a complex with crown 4. Similarly, Na⁺ and K⁺ prefers crown 5 and crown 6 respectively.

Crypt (cryptate has hidden)

Cryptate is the three-dimensional equivalent of a crown ether having N-atoms as an extra donor site in addition to O-atoms. The ligand completely wraps the central metal atoms and hide it in the centre. hence, the name crypt (crypt hide).

Crypt has strongly (better) complexing ability than crown ether. Example

Example.

The typical crypt is the molecule N(CH₂-CH₂-O-CH₂-CH₂-OCH₂-CH₂)₃N. This is called cryptate-222.

The biological importance of Crown and Crypt.

Some of the biological importance of crown and crypt are as follows.

1. Natural biological crown ether transfer metal ions. ( eg;Na⁺, K⁺) inside and outside of the cell through a cell membrane. Hence, it acts as phase transfer catalyst.
2. Crown ether is used to isolate specific metal ions from the ionic mixture.
3. It can be used to stabilise unusual oxidation. For example, it is possible to product Na- ion iodide ion in the compound-[222-crypt-Na⁺) Na^-
4. Crown ether is used to isolate the specific metal ions from the ionic mixture.

Reference.

F.A.Cotton and Wilkinson G. Basic inorganic Chemistry. John,Wiley and Sons (Asia), 2007.

Lee., J.D. Concise Inorganic Chemistry. fifth edition. New Delhi: Oxford University Press., 2008.

Sharma, M.L and P.N Chaudhary. A textbook of B.S.C chemistry. Kathmandu Nepal: Ekta Books Thapathali Kathmandu, 2011.

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