| 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 of the periodic table of elements consists of the first two groups: the alkali metals and alkaline earth metals, plus hydrogen and helium.
Except in hydrogen and helium, these electrons are very easily lost to form positive ions. The helium configuration is chemically exceedingly stable and thus helium has no known stable compounds; thus it is generally grouped with the noble gases. 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 isolated rubidium nine years later after having observed it and caesium spectroscopically. Caesium was not isolated until 1881 when Carl Setterberg electrolysed the molten cyanide.
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.
The modern periodic law state that chemical and physical properties of the element are periodic function of their atomic number.The long form of periodic table is based on modern periodic law. The long form of periodic table 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.
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 group. In these anomalous propeties they resemble the second element of the succeeding group. Thus lithium shows similarities to Magnesium and Beryllium to aluminium 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 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:
Anomalous behaviour of lithium Lithium-the first element of group 1 differs from rest of this group in many respects contrary to the expectations. This anomalous behaviour of lithium is due to the following reasons :- a. very 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. Li form monoxide with oxygen, other alkali form peroxide and superoxide. 4. Li combines with nitrogen to form nitrides while other alkali metals do not. 5. LiCl is deliquescent and crystallizes as a hydrates LiCl.2h2o,whereas other alkali metal chlorides do not form hydrates.
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