Introduction
The long form of the periodic table is based upon the filling of a particular shell and has been accordingly divided into four blocks i.e. 's', 'p', 'd' and 'f' blocks. The 's' block elements involve the filling of 's' subshell. This block includes the elements of group 1 (or I A) and group 2 (or II A). They have one or two electrons in their outermost 's' subshell respectively.
General Features of the 's' Block
Alkali and alkaline Earth metals are the most violently active of all the metals. These occur in the combined form with halide, sulphate, carbonate, silicate ions, etc. and are not found in the free state in nature, as these are readily oxidized.
Alkali Metals
The six elements belonging to group 1 of the periodic table, namely lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr) are called alkali metals. They constitute alkali metals because they readily dissolve in water to form hydroxides, which are strongly alkaline in nature. They also form alkaline oxides. The element francium is radioactive.
Chemical Characteristics of Alkali Metals
Alkali metals exhibit a high chemical reactivity because of their
* low ionization energies.
* low heat of atomization.
Anomalous behavior of Lithium
Lithium displays most of the characteristic properties of group to which it belongs i.e. the alkali metals group (Group 1).
Lithium and Sodium - Extraction
Due to their being highly reactive, alkali metals do not occur in free state. However in the combined form, they occur widely in nature.
Physical Properties of Lithium and Sodium
Lithium and sodium are light, soft metals with silvery white lustre. Lithium is harder than sodium.
Chemical Properties of Lithium and Sodium
Both lithium and sodium are extremely reactive metals. Sodium is more reactive than lithium.
Uses of Lithium and Sodium
In the manufacture of sodium peroxide, sodamide, sodium cyanide etc. About 50 per cent of sodium extracted is used in the manufacture of tetraethyl lead (C2H5)4Pb), which is used as anti-knock agent in petrol.
Compounds of Sodium - Sodium Carbonate
Sodium forms many industrially important compounds like halides, carbonates, sulphates and hydroxides. The compounds of sodium are ionic in nature and are readily soluble in water.
Alkaline Earth Metals
The elements of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra), constitute group 2 of the periodic table.
Chemical Properties of Alkaline Earth Metals
As alkaline Earth metals have low ionization energies and high electropositive character, they are very reactive and have a strong tendency to lose valence electrons, though less than alkali metals. The reactivity of these elements increases on going down the group. The chemistry is governed by dipositive oxidation state (M2+).
Solubility and Thermal Stability of the oxo Salts of 'S' Block Elements
The carbonates and sulphates of alkaline Earth metals are less soluble than corresponding metal salts. Their solubility decreases down the group as a result of decrease in the hydration energy. For example, MgCO3 is slightly soluble in water whereas BaCO3 is almost insoluble. Similarly, magnesium sulphate is soluble in water, calcium sulphate is slightly soluble while SrSO4 and BaSO4 are insoluble.
Differences between Beryllium and Magnesium
Beryllium is the first member of the alkaline earth metals family. When compared to magnesium and the rest of the members, beryllium shows anomalous behavior, mainly because of the following reasons:
* Small size of the atom or its ion
* High ionization energy and electronegativity
* Absence of 'd' orbitals.
Diagonal Similarities of Beryllium and Aluminium
Due to diagonal relationship existing between beryllium and aluminium, they both show some similarities.
* Both Be and Al form covalent compounds.
* On treatment with concentrated HNO3, both beryllium and aluminium are rendered passive.
* Both form complexes.
Magnesium
Magnesium belongs to group 2 of the periodic table along with other elements like Calcium (Ca), beryllium (Be), strontium (Sr), barium (Ba) and radium (Ra). These elements are called alkaline Earth metals. Due to their smaller size, the electrons are more tightly bound in them and so the first ionization energies are higher than those of the corresponding group 1 elements. The second ionization energies are almost twice the first ionization energies in these elements. Magnesium forms bipositive cations, but they are less electropositive than the alkali elements. In view of the smaller size of the atoms and ions, alkaline earth metals are denser and harder than the alkali metals and have higher melting points.
Compounds of Magnesium and Calcium
Magnesium and calcium form dipositive ions. They form compounds with many non-metals. The compounds are generally ionic. Unlike the salts of alkali metals, those of magnesium and calcium are not always readily soluble in water.
Cement
Cement is one of the most important modern building materials. It finds application in the construction of buildings, roads, dams and bridges. It is obtained by combining a lime-rich material with the one containing silica and alumina.
