This is the notes for alkaline earth metals.
Alkaline earth metals:
The element of group IIA in periodic table are called alkaline earth metal because their oxides are are very stable to heat and form bases when reacted with water. Alkaline earth metal exist in Earth crust predominantly.
Example: Mg + H2O → Mg(OH)2 ( Alkali )
General characteristics of alkaline earth metals:
Physical characteristics:
1. Appearance :alkaline earth metals are silvery white when freshly cut but turnish in air.
2. Physical state: alkaline earth metals are soft but harder than alkali metal due to stronger metallic bond.
3. Atomic size: Alkaline earth metals have the large atomic size but smaller than alkali metals.
4. Melting and boiling point: Alkaline earth metals have low melting point and boiling point but higher than that of alkali metals.
5. Ionization energy: they have lower ionization energy but I rather than that of alkali metals.
6. Conductivity: They are excellent conductor of electricity.
7. Electronegativity: they have lower electronegativities but higher than that of alkali metals.
8. Flame colour: Alkaline earth metals accept Be and Mg impart characteristic colour in Bunsen flame.
Chemical characteristics of alkaline earth metal:
They are highly reactive always show + 2 Oxidation State and typically form ionic compounds.
Some important compound of alkaline earth metals:
A. Quick lime ( CaO ), : Quick lime is chemically calcium oxide( CaO ) and also called burnt lime or simply lime . It is call Chuna in Nepali .
Uses:
1. It is Chief constituent of cement which is a most widely used building material.
2. It is used in manufacture of glass , bleaching powder etc.
3. It is used as refractory material for lining of furnaceas it has high melting point.
4. It is used as flux in Metallurgy.
CaO ( flux ) + SiO2 ( impurity) →CaSiO3 ( Calcium silicate: Slag )
5. It is used as drying agent.
6. It is used in agriculture to neutralize acid
7. it provides suitable environment for fish breeding.
B. Bleaching powder ( CaOCl2 )
Bleaching powder is chemically calcium chlorohypochlorite Ca(ClO)Cl and it is also called chlorinated lime.
Uses:
1. It is used as bleaching agent in textile industry.
2. It is used in manufacture of chloroform which is an important organic compound.
3. It is used as germicide and disinfectant in the purification of drinking water.
4. It is used for removing poisonous gases from air during the war time.
5. It is used in oxidising agent in industries.
C. Magnesia ( MgO )
Magnesia is chemically magnesium oxide; ( MgO )
Uses:
1. Due to its high melting point, it is used as refractory materials in lining of furnaces.
2. It is also used to prepare crucibles and cupels in metallurgical process.
3. Its aqueous suspension is called milk of magnesia which is used as antacid.
D. Plaster of Paris ( CaSO4 .1/2H2O )
The name is given due to its preparation from gypsum rock abundantly found near Paris and due to its property that it hardens when moistened and allowed to dry.
Uses:
1. In construction work: Indoor use, false wall, false ceiling, inner wall etc it is because it is easily shaped into different geometry and naturalistic structure.
2. In movie and theatrical seat it is used to simulate appearance of wood, stone, metal etc.
3. In medicine it is used as orthopedic cast for encasing limbs and in some cases large portion of the body.
4. It releases water water vapour in fire and the process is endothermic, hence slows down the spread of fire. Therefore it is useful in fire protection.
E. Epsom salt ( MgSO4 .7H2O )
Epsom salt is chemically magnesium sulphate heptahydrate ( MgSO4 .7H2O ). The name is given because of its preparation of originally from Epsom spring of England.
Uses:
1. Which is used as purgative in medicines.
2. Which is used to correct magnesium and sulphur deficiency of soil.
3. Anhydrous form is used as dessiccant.
4. Used it is used as laboratory reagent.
5. Used in manufacture of paints soap and fireproofing.
Solubility of hydroxides, carbonates and sulphate of alkaline earth metals
Hydroxides, carbonate and sulphate of alkaline earth metals are most common compounds. These compounds are more or less soluble in water.
Solubility of hydroxide:
Alkaline earth metal forms basic oxide which are fairly soluble in water forming corresponding basic hydroxide. The solubility of group II A metal hydroxide goes on increasing on moving from top to bottom in the group. Therefore, barium hydroxide is most soluble hydroxide in the group. The barium hydroxide is as soluble as some of the alkali metal. General trend of solubility is,
Be(0H)2 < Mg(OH)2 < Ca(OH)2 < Sr(OH)2 < Ba(OH)2
Solubility of carbonate:
Solubility of group IIA metal carbonate decreases down the group, Therefore, barium carbonate is most insoluble carbonate in the group. The general solubility trend of group IIA metal carbonate is,
BeC03 > MgC03 > CaC03 > SrC03 > BaC03
Solubility of sulphate:
Solubility of group IIA metal sulphate decreases down the group. Therefore, barium sulphate is most insoluble sulphate salt in the group. The generalsolubility trend of group IIA metal sulphate is,
BeS04 > MgS04 > CaS04 > SrS04 > BaS04
Beryllium sulphate and magnesium sulphates are soluble in water but calcium, sulphate is sparingly soluble in water, strontium sulphate and barium sulphates are virtually insoluble.
Stability of carbonate and nitrate of alkaline earth metals:
Carbonate, nitrate, and sulphate of alkaline earth metal are stable compounds. The general trend of stability of these compounds are briefly describe below,
Stability of carbonate : Group IIA metal carbonate are fairly Stable to heat. Their thermal stability goes on increasing from top to bottom along the group. This can be understood from their thermal decomposition temperature.
Stability of nitrate: Group IIA metal nitrate decompose to give corresponding metal oxide upon heating.
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