s-block

Chemical elements in s-block

Group	1	2	18
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 element of the periodic table consists of the first two groups: the alkali metals and alkaline earth metals, plus hydrogen and helium.

Except in hydrogen and helium, their electrons are very easily lost to form positive ions. Helium's configuration is exceedingly chemically stable and thus helium has no known stable compounds; thus it is generally grouped with the noble gases.^{[citation needed]} The 1st A group is called alkali metals, and 2nd A is called alkyne earth metals.

Excluding hydrogen and helium, the elements of the s-block are all extremely powerful reducing agents, so much so that they never occur naturally in the free state. The metallic forms of these elements can only be extracted by electrolysis of a molten salt, since water is much more easily reduced to hydrogen than the ions of these metals. Sir Humphry Davy, in 1807 and 1808, was the first to isolate all of these metals except lithium, beryllium, rubidium and caesium. Beryllium was isolated independently by F. Wooler and A.A. Bussy in 1828, while lithium was isolated by Robert Bunsen in 1854, who also isolated rubidium nine years later after having observed it and caesium spectroscopically. Caesium was not isolated until 1881 when Carl Setterberg electrolysed molten cyanide.^{[citation needed]}

The s-block metals vary from extremely soft (all the alkali metals) to quite hard (beryllium). With the exception of beryllium and magnesium, the metals are too reactive for any structural use except as very minor components (<2%) of alloys with lead.^{[citation needed]}

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 i.e. S,P,D,F. In an atom of 's' block element,the last electron enters 's' orbital of the outermost orbit.

Group-1:

Hydrogen (Z=1), Lithium (Z=3), Sodium (Z=11), pottasium (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

Lithium and Beryllium, the first elements in group 1 and group 2 respectively, show some properties which are different from other from other members of their respective groups. In these anomalous properties they resemble the second element of the succeeding group. Thus lithium shows similarities to magnesium and beryllium to aluminum in many of their properties.

       Group→      1    2   13    14
       Period 2   Li   Be   B     C
       Period 3   Na   Mg   Al    Si

This type of relationship in the periodic table is known as a Diagonal relationship. The diagonal relationship is due to the similarities in ionic sizes and charge/radius ratio of the element. The similarity between lithium and magnesium is due to their same sizes:

Radii, Li=152pm Mg=160pm

Anomalous behaviour of lithium Lithium-the first element of group 1 differs from rest of this group in many respects. This anomalous behaviour of lithium is due to the following reasons: a. small size of lithium atom and its ion. b. 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 c. comparatively high ionisation enthalpy and low electropositive character of lithium as compared to other alkali metals d. non availability of d-orbitals in its valence shell e. strong intermetallic bonding Some of the properties in which lithium differs from other members of its group illustrating its anomalous behaviour are as follows: 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.

See also

• Electron configuration