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S-block Elements

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The elements in groups 1 and 2 and helium in group 18 of the periodic table are known as s-block elements. Apart from hydrogen and helium all the elements of s-block are metals. The metals lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium which belongs to group 1 are called alkali metals because they react with water to form hydroxides which are strong bases or alkalies.


S-block has two groups of elements. The first group is called alkali metals and the next one is known as alkaline earth metals. Both of them have s orbital as the outermost orbital. S-block elements are highly electropositive in nature and they mostly form cations in the formation of electrovalent compound.


The S-block elements in Group I are highly reactive but those in Group II are slightly less so and show a rather more obvious trend in reactivity. The elements are metals, excellent conductors of electricity and typically soft and highly reactive. They have one loosely held valence electron in their outer shell, and typically form univalent ionic and colorless compounds.

S Block on Periodic Table

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The periodic table can be divided into four regions or blocks of elements according to the orbitals being filled. The groups 1A and 2A elements on the left side of the table are called the s-block elements because they result from the filling of an s orbital.

S Block on Periodic Table
  1. The elements of the periodic table in which the last electron enters in s-orbital are called s-block elements.
  2. S-orbital can accommodate a maximum of two electrons.
  3. Their general formula are ns1 and ns2 respectively, where n=(1 to 7).
  4. IA group elements are known as alkali metals because they react with water to form alkali. IIA group elements are known as alkaline earth metals because their oxides react with water to form alkali and these are found in the soil or earth.
  5. The total number of s-block elements are 13 (including hydrogen).
  6. Fr and Ra are radioactive elements while H is gaseous element.
  7. Cs and Fr are liquid elements belonging to s-block.

Alkali and Alkaline Earth Metals

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Alkali metals


Alkali metals are placed in Group 1A of the periodic table. These elements have one electron each in their outermost shell. They form compounds by giving up this electron to an electron accepting atom and leaving being an ion with a positive charge and a stable electronic configuration of a noble gas.

Alkaline earth metals


Alkaline earth metals are placed in Group IIA of the periodic table. The alkaline earth metals have two electrons each in their outermost shell. Alkaline earth metals are moderately electropositive. It hydrolyze more readily than alkali metals.

S.No Alkali metals
Alkaline earth metals
1
Lithium
Beryllium
2
Sodium
Magnesium
3
Potassium
Calcium
4
Rubidium
Strontium
5
Cesium
Barium

Differences between alkali and alkaline earth metals


S.No
Alkali metals
Alkaline earth metals
1
They are soft.
They are hard.
2
They have low melting points. They have relatively high melting points.
3
Hydroxides are strongly basic.
Hydroxides are relatively less basic.
4
Carbonates do not decompose.
Carbonates decompose to form oxides on strong heating.
5
On heating nitrates give the corresponding nitrites and oxygen. On heating nitrates give the corresponding oxides, nitrogen dioxides and oxygen.
6
Hydroxides are stable on heating.
Hydroxides form oxides on heating.
7
Bicarbonates of alkali metals are stable solids at room temperature.
Bicarbonates exist only in solution state at room temperature.
8
They form peroxides on heating.
Only barium form peroxides on heating.
9
They do not form nitrides except for lithium.
They form stable nitrides when heated directly with nitrogen.
10
They do not form carbides except for lithium. They form stable carbides on heating with carbon.
The elements of group I (alkali metals) and group 2 (alkaline earth elements) which have ns1 and ns2 outermost electronic configuration respectively belong to s-block elements.

The electronic configuration of alkali metals and their atomic number are listed below.

Alkali metals
Li
3 1s22s2
Na
11
[Ne] 3s1
K
19
[Ar] 4s1
Rb
37
[Kr] 5s1
Cs
55
[Xe] 6s1

The electronic configuration of alkaline earth metals and their atomic number are given below.

Alkaline earth metals
Be
4
1s22s2
Mg
12
[Ne] 3s2
Ca
20
[Ar] 4s2
Sr
38
[Kr] 5s2
Ba
56
[Xe] 6s2

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Diagonal Relationship

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Elements of second period are known as bridge elements. Properties of the bridge elements resemble with the properties of the diagonal elements of the third period. For example, Li resembles Mg, Be resembles Al, B resembles Si etc.

Lithium shows similarity in its properties with magnesium. This diagonal similarity is known as diagonal relationship. This is due to similarity in their charge/radius ratio.

Diagonal Relationship

Because of the diagonal relationship between lithium and magnesium they show similarities in properties.
  1. Both have high boiling points.
  2. Both form normal oxides Li2O and MgO.
  3. Both form an ionic nitride with nitrogen.
  4. The carbonates and nitrates of Li and Mg decompose to oxide on heating.
  5. The salts of both Li and Mg are heavily hydrated.
  6. The carbonate, fluoride and phosphate of both are insoluble in water.
  7. Both the elements directly combine with carbon to form carbides.
  8. Both LiCl and MgCl2 are soluble in alcohol and other organic solvents.
  9. LiClO4 and Mg(ClO4) are soluble in alcohol.
  10. Both the elements are strongly complexed by N donors than heavier metals.

Chemical Properties

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The elements of group I (alkali metals) and 2 (alkaline earth metals) are s-block elements. In all these elements the last electron enters in the s-orbital. The general properties of s-block elements are listed below.
  1. The electronic configuration of their outer most orbit is ns1-2.
  2. They are highly electropositive and possess low ionization energy.
  3. They are soft metals with low boiling point and melting point.
  4. They react by losing electrons and exhibit mono and di valencies respectively.
  5. They act as powerful reducing agents.
  6. They form colored compounds.
  7. They impart characteristic colors to the flame.

Properties of Lithium

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The properties of lithium are quite different from the properties of other alkali metals. The main reasons for the anomalous behavior of lithium as compared to other alkali metals are
  1. The extremely small size of lithium atom and its ion.
  2. Lithium conducts heat and electricity as all metals do.
  3. Greater polarizing power of lithium ion due to its small size which results in the greater covalent character in the compounds.
  4. Least electropositive character and highest ionization energy as compared to other alkali metals.

Lithium Uses

  1. Lithium compounds have a number of uses in industry and medicine.
  2. Lithium carbonate is used as a starting material for the manufacture of many other lithium compounds.
  3. It is an ingredient of specialty glasses, enamels and specialty ceramic ware having low thermal expansion coefficients.
  4. Lithium carbonate is widely prescribed as a drug to treat acute mania in manic-depressive and schizo-affective metal disorders.
  5. Lithium hydroxide is an ingredient in the manufacture of lubricant greases and in some long life alkaline storage batteries.