s-block

s-block in the periodic table
	1	2	18
Group →
↓ Period
1	1 H		2 He
2	3 Li	4 Be
3	11 Na	12 Mg
4	19 K	20 Ca
5	37 Rb	38 Sr
6	55 Cs	56 Ba
7	87 Fr	88 Ra

The s-block is a block in the periodic table that consists of the first two groups, namely the alkali metals and the alkaline earth metals. The elements in the s-block generally exhibit well-defined trends in their physical and chemical properties, changing steadily moving down the groups. Their properties can be most readily explained in terms of their electron configuration, with their valence electrons occupying s-orbitals. By this definition, hydrogen and helium are sometimes also considered to be part of the s-block.

Properties

The modern periodic law states that an element's chemical and physical properties is a periodic function of its atomic number. The long form of the periodic table is based on modern periodic law. The long form is divided into four blocks, s, p, d, and f. In an atom of an s-block element,the last electron enters the s-orbital of the outermost electron shell:

Group 1:

Hydrogen (Z=1), Lithium (Z=3), Sodium (Z=11), Potassium (Z=19), Rubidium (Z=37), Caesium (Z=55), Francium (Z=87).

Group 2:

Beryllium (Z=4), Magnesium (Z=12), Calcium (Z=20), Strontium (Z=38), Barium (Z=56), Radium (Z=88).

Anomalous properties of Lithium:

Among alkali metal cations, lithium has the smallest size and highest polarizing power. This separates lithium from its family members. Its covalence character is higher, which is responsible for its solubility in organic solvent.

Diagonal relationship

1.) Lithium is in group 1 and period 2. 2) magnesium is in 2 group and 3 period. 3.) Lithium resembles magnesium which is diagonally placed. ¤ Cause of diagonal relationship- lithium and magnesium have similar ionic size and polarizing power hence they show diagonal relationship. ¤ Similarities between lithium and magnesium- Due to similar ionic size and polarizing power. ' Li ' and ' mg ' shows similar properties. 1) Both Li and mg are hard metals. 2) Licl and Mgcl2 are deliquecent and crystallize as hydrates. Licl.2H2o and Mgcl.2H2O. 3) both Li and mg combine with nitrogen to form nitrides. 4) hydroxides of both Li and mg are weak bases. 5) carbonates of both Li and mg decompose on heating. 6) hydrogen carbonates of both Li and mg do not exist in solid states.

Anomalous behaviour of lithium

Lithium - the first element of group 1 - differs from the rest of this group in many respects. This anomalous behaviour of lithium is due to the following reasons:

1. small size of lithium atom and its ion.
2. higher polarization power of Li⁺ (i.e. charge size ratio) resulting in increased covalent character of its compounds which is responsible for their solubility in organic solvents
3. comparatively high ionisation enthalpy and low electropositive character of lithium as compared to other alkali metals
4. strong intermetallic bonding

Some of the properties in which lithium differs from other members of its group illustrating its anomalous behaviour are as follows:^{[citation needed]}

1. Lithium is harder than sodium and potassium which are so soft that they can be cut by a knife.
2. The melting and boiling points of lithium are comparatively high.
3. Lithium forms monoxide with oxygen, other alkali form peroxide and superoxide.
4. Lithium combines with nitrogen to form nitrides, while other alkali metals do not.
5. Lithium Chloride is deliquescent and crystallizes as a hydrate LiCl.2H2O, whereas other alkali metal chlorides do not form hydrates.
6. hydroxide of alkali metals don't decompose but LiOH decompose in Li2O+H2O
7. lithium carbonate decompose on heating into Li2O+CO2 but rest of all decompose as MOH+H2O+CO2
8. alkali nitrate make nitrites and O2 on heating but Li2NO3 decompose into Li2O and gives brown colour gas NO2 and O2

See also

• Electron configuration