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The s-block elements consist of the elements in which the outermost electrons enter into the s-orbital. These elements are divided into two categories i.e, alkali metals or group 1 elements and alkaline earth metals or group 2 elements. Their oxides and hydroxides are alkaline in nature. The general electronic configuration of these elements is ns1 and ns2 respectively. The first element of these groups i.e, lithium and beryllium show deviation in their properties from their respective group and they resemble the second element of the following group. This is known as the diagonal relationship.
These elements have a large number of applications in our daily life such as washing Soda, it is also known as sodium carbonate. It is used for various purposes such as water softening, manufacture of glass, paper, paints, etc.
Limestone is also one of the important compounds of the s-block element. It is used to neutralize the acidic soils. It has various other applications as well such as, for making cement, in glassmaking industry and in construction works, etc.
There are also various other applications of s-block elements. In this article, you will get every important information regarding this chapter like important topics, how to prepare for this chapter and important books for preparation.
Notes for s-block Elements
Important Topics
- Group 1 element- Alkali Metals
- Physical Properties
- Chemical Properties
- General characteristics of the compounds of the Alkali Metals
- Anomalous properties of Lithium
- Some important compounds of Sodium
- Biological Importance of Sodium and Potassium
- Group 2 elements: Alkaline Earth Metals
- Physical Properties
- Chemical Properties
- General characteristics of the compounds of the Alkaline Earth Metals
- Anomalous behaviour of Beryllium
- Some important compounds of Calcium
- Biological importance of Magnesium and Calcium
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Overview of the Chapter - s-block Elements
The s-block elements are those in which the outermost electrons exist in s-orbital. Alkali and alkaline earth metals are respectively the members of group 1 and group 2 elements. In this chapter, there are various important properties that you need to learn such as electronic configuration, ionization enthalpy, hydration enthalpy, chemical properties, etc.
Group 1 elements: Alkali metals
(i) Electronic configuration: The alkali metals or group 1 elements have the valence shell electronic configuration is ns1. The table given below describes the electronic configuration of the alkali metals.
| Element |
Symbol |
Electronic configuration |
| Lithium |
Li |
[He] 2s1 |
| Sodium |
Na |
[Ne] 3s1 |
| Potassium |
K |
[Ar] 4s1 |
| Rubidium |
Rb |
[Kr] 5s1 |
| Caesium |
Cs |
[Xe] 6s1 |
| Francium |
Fr |
[Rn] 7s1 |
(ii) Atomic and ionic radii: Alkali metal atoms have the largest sizes in their respective periods. This atomic size decreases as we move along the period and increases as we move down the group.
(iii) Ionization Enthalpy: The ionization enthalpy of the alkali metal atoms are low as compared to other atoms in their respective periods. This is because of the larger size of these atoms. As we move down the group, the ionization enthalpy further decreases because of the larger size of the atoms.
(iv) Chemical Properties
- Reactivity towards air: Alkali metals react too fast with oxygen and form oxides. Lithium being the smallest element forms monoxide, sodium forms peroxide and other large metals form superoxides.
All these metals in their oxides have the oxidation number equal to +1.
- Reactivity towards water: Alkali metals react with water to form hydroxides and dihydrogen.
- Reactivity towards dihydrogen: Alkali metals react with dihydrogen and form hydrides.
- Reactivity towards halogens: Alkali metals react too fast with halogen elements to form alkali halides.
- Alkali metals with ammonia: These metals dissolve in liquid ammonia giving the deep blue solution.
![M\: +\: (x+y)NH_{3}\, \rightarrow \, [M(NH_{3})_{x}]^{+}\: +\: [e(NH_{3})_{y}]^{-}](https://entrancecorner.codecogs.com/gif.latex?M%5C%3A%20+%5C%3A%20%28x+y%29NH_%7B3%7D%5C%2C%20%5Crightarrow%20%5C%2C%20%5BM%28NH_%7B3%7D%29_%7Bx%7D%5D%5E%7B+%7D%5C%3A%20+%5C%3A%20%5Be%28NH_%7B3%7D%29_%7By%7D%5D%5E%7B-%7D)
Anomalous Properties of Lithium
The deviation of the behaviour of lithium from its respective elements is because of two factors:
(i) The exceptionally small size of the atom
(ii) High polarising power
Because of these above two factors, lithium has some point of differences between other alkali metals and some similarities with magnesium.
(i) Differences between Lithium and other alkali metals
- Lithium is harder and it's melting point and boiling point are also higher than other alkali metals.
- Lithium is least reactive than other alkali metals.
- Lithium does not form solid hydrogen carbonate, unlike other alkali metals.
- Lithium does not form ethynide on reaction with ethyne, unlike other alkali metals.
- Lithium nitrate on heating gives lithium oxide but other alkali metal nitrates produce metal nitrite.
- Fluorides and oxides of lithium are less soluble in water than those of other alkali metals.
(ii) Similarities between Lithium and Magnesium
The similarity between lithium and magnesium is also known as the diagonal relationship with magnesium. This similarity of lithium and magnesium arises because of their similar sizes.
- Lithium and Magnesium, both are harder and lighter than their respective group elements.
- Their oxides and hydroxides are less soluble.
- Both oxides of lithium and magnesium do not combine with excess oxygen.
- The chlorides of both lithium and magnesium are soluble in ethanol.
- Both form nitride on reaction with nitrogen, known as Lithium Nitride and Magnesium Nitride.
Some Important Compounds of Sodium
There are some important compounds of sodium from industrial basis. Their production and uses are discussed below.
(i) Sodium Carbonate
(ii) Sodium Chloride
(iii) Sodium Hydroxide
(iv) Sodium Hydrogencarbonate
Group 2 elements: Alkaline Earth Metals
(i) Electronic configuration: The alkaline earth metals or group 2 elements have the valence shell electronic configuration is ns2. The table given below describes the electronic configuration of the alkali metals.
| Element |
Symbol |
Electronic configuration |
| Beryllium |
Be |
[He] 2s2 |
| Magnesium |
Mg |
[Ne] 3s2 |
| Calcium |
Ca |
[Ar] 4s2 |
| Strontium |
Sr |
[Kr] 5s2 |
| Barium |
Ba |
[Xe] 6s2 |
| Radium |
Ra |
[Rn] 7s2 |
(ii) Atomic and ionic radii: Alkaline earth metal atoms have larger sizes than other metal atoms in their respective periods but smaller than the alkali metals. This atomic size decreases as we move along the period and increases as we move down the group.
(iii) Ionization Enthalpy: The ionization enthalpy of the alkali metal atoms are low as compared to other atoms in their respective periods but higher than the alkali metal atoms. As we move down the group, the ionization enthalpy further decreases because of the larger size of the atoms.
(iv) Chemical Properties
- Reactivity towards air and water: Beryllium and magnesium are usually inert as they are covered with an oxide film on their surface. But the powdered beryllium burns in air and forms beryllium oxide. Other heavier elements of this group readily react with air and form oxides.
- Reactivity towards halogens: All alkaline earth metals combine with halogen to form the halides.
- Reactivity towards hydrogen: Except beryllium, all other alkaline earth metals combine with hydrogen to form their hydrides.
- Reactivity towards acids: The alkaline earth metals react with acids and liberate hydrogen.
- Alkaline earth metals with ammonia: These metals dissolve in liquid ammonia and give blue-black solution.
![M\: +\: (x+y)NH_{3}\, \rightarrow \, [M(NH_{3})_{x}]^{2+}\: +\: 2[e(NH_{3})_{y}]^{-}](https://entrancecorner.codecogs.com/gif.latex?M%5C%3A%20+%5C%3A%20%28x+y%29NH_%7B3%7D%5C%2C%20%5Crightarrow%20%5C%2C%20%5BM%28NH_%7B3%7D%29_%7Bx%7D%5D%5E%7B2+%7D%5C%3A%20+%5C%3A%202%5Be%28NH_%7B3%7D%29_%7By%7D%5D%5E%7B-%7D)
Diagonal Relationship between Beryllium and Aluminium:
-
Aluminum and Beryllium both have oxide film on their surface thus are not easily attacked by acids.
-
Both aluminum hydroxide and beryllium hydroxide react with alkali to form beryllate and aluminate ions
- Both aluminum and beryllium react with chlorine and form polymeric chlorides. These chlorides are soluble in organic solvents.
- Aluminum and Beryllium ions, both have a strong tendency to form complexes.
Some Important Compounds of Calcium
(i) Calcium Oxide or Quick Lime(CaO)
(ii) Calcium Hydroxide (Slaked lime), Ca(OH)2
(iii) Calcium Carbonate, CaCO3
(iv) Calcium Sulphate (Plaster of Paris), CaSO4·H2O
How to prepare for p-Block elements?
-
This chapter is a part of inorganic chemistry. It is completely theory-based and very easy to learn, no need to memorize any formula.
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Before reading this chapter, first, you must have the basic knowledge of chapter - periodic classification of elements.
-
You must also learn why there are some elements like Boron and Carbon show anomalous behaviour with respect to other elements in their group.
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Rest this complete chapter is very simple, just be regular and be consistent in your numerical practice.
Prescribed Books
First, you must finish the class XI textbook and solve each and every example and unsolved question given in it. Then for advanced level preparation like JEE and NEET, you must follow O.P. Tandon or Solomons and Fryhle. You must definitely solve the previous year papers. Meanwhile, in the preparation, you must continuously give the mock tests for the depth of knowledge. Our platform will help you to provide with the variety of questions for deeper knowledge with the help of videos, articles and mock tests.
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