S Block elements Notes for class 12th / NEET / Physical and properties of S block elements , Diagonal relationship, Notes of S block elements

                                          S Block Elements

The elements of group IA and group IIA of the periodic table constitute s-block elements

Elements of group IA

                           IA sub-group of the periodic table consist of six elements – Lithium, sodium, potassium, rubidium, caesium and francium . they are known as Alkali metals.

Physical properties of group IA –

                              

v Electronic configuration- the electronic configuration of these elements are as fallows.

Li3 – 1s^{2 ,} 2s²

Na₁₁- 1s², 2s², 2p⁶, 3s²

K₁₉- 1s² , 2s², 2p⁶ , 3s², 3p⁶, 4s²

Rb₃₇- 1s², 2s², 2p⁶ , 3s², 3p⁶, 3d¹⁰, 4s², 4p⁶, 5s²

Cs₅₅ – 1s², 2s²,2p⁶, 3s², 3p⁶, 3d¹⁰, 4s², 4p⁶, 4d¹⁰, 5s², 5p⁶ , 6s²

Fr₈₇ - 1s², 2s², 2p⁶, 3s², 3p⁶, 3d¹⁰, 4s², 4p⁶, 4d¹⁰ , 4f¹⁴, 5s², 5p⁶, 5d¹⁰, 6s², 6p⁶, 7s²

From the above electronic configuration it may be concluded that these elements have the general outermost electronic configuration as ns¹

v Physical state-

                  All the elements are soft silver white metal . lithium though hardest of the alkali metals can be cut with knife.

                                                                                 

v Melting and boiling point-

                      Their melting and boiling points are low and decrease from lithium to caesium.

 

v Atomi and ionic radii-

                      Atomic and ionic radii of alkali metal atoms are largest . their values gradually increases on going down the group from Li to Cs

 

v Density-

               Alkali metals have very low density due to their large atomic size. Their density gradually increases as the atomic number increases.

 

v Electronegativity-

             Alkali metals have very low electronegativity which decreases from lithium to caesium.

 

v Colour and diamagnetic character-

            The ions of the alkali metals are colourless and diamagnetic because the electrons are fully paired in them

 

 

·     Chemical properties of group IA –

 

Ø  Chemical reactivity-  

                         Since ionosation potential of alkali metals are very low, they are very reactive metals. Their reactivity increase from lithium to caesium.

 

Ø Action of water-

                       They react vigorously with cold water evolving H₂

 

  2Na + 2H₂O     2NaOH                        

 

The reactivity towards water increases from lithium to caesium

 

Ø Action of alcohols-

                         Like water they also evolve H₂ when added to alcohol

              

Ø Action of acids-

                  Alkali metals react with acids and evolve H₂.

                2Na + H₂SO₄           Na₂SO₄ + H₂

 

·         Diagonal relationship of lithium with

       magnesium –

                            Lithium differs in many respects from the other members of its family but shows close resemblance with Mo placed diagonally in the periodic table as shown below :

 

 

                

 

 

Lithium differs from the alkali metals and resembles Mg in the following respect.

v Both Li and Mg have nearly the same atomic volume

and ionic radii in crystals.

v Both the metals have nearly the same electropositive

character.                                                                                                                                                 

v  Li and Mg both are hard metal.

v  The melting and boiling points of both Li and Mg are much higher.

 

 

 

Physical properties of of group IIA-

 

v Electronic configuration -  The electronic configuration of                    

these elements is as follows

 

Be₄ = 1_S², 2s²

 

Mg₁₂ = 1s², 2s², 2p⁶, 3s²

 

Ca₂₀ = 1s², 2s^2,, 2p⁶, 3s², 3p⁶, 4s²

                                                                                                     Sr₃₈ = 1s², 2s² , 2p⁶, 3s² , 3p⁶ , 3d¹⁰ , 4s² ,4p⁶ , 5s²               

Ba₅₆ = 1s² , 2s² , 2p6, 3s² , 3p⁶ ,3d10, 4s² , 4p⁶, 4d¹⁰, 5s² ,5p⁶   

               6s²

 

Ra₈₈ = 1s² , 2s², 2p ,3s² , 3p⁶, 3d¹⁰,  4s², 4p⁶, 4d¹⁰, 4f¹⁴,   5s², 5p⁶,    

 

5d¹⁰  , 6s²,  6p⁶ , 7s²  

              

 

 

From the above electronic configuration, it may be concluded that these elements have the general outermost electronic configuration as ns2 .

 

 

v . Physical State -  They are greyish-white, light, melleable and ductile metals. They are harder than the alkali metals. The hardness gradually decreases with the increase in atomic number.

 

 

v . Melting and Boiling Points - Their melting and boiling points are higher than those of alkali metals. They do not show regular trend.

 

v . Atomic and Ionic Radii - Both atomic and ionic radii of alkaline earth metals are smaller than those of alkali metals. Both increase as we go down the group from beryllium to radium.

 

v Density - These metals have higher density than that of the alkali metals. Their density decreases upto calcium and then increases

 

v . Ionisation potential -  Due to smaller size, their ionisation potential is higher than that of alkali metals. Their first and second ionisation potential decrease as the atomic number increases

 

v . Electronegativity – The alkaline earth metals have low electronegativity value which decreases from beryllium to radium

 

 

·         Diagonal relationship between Beryllium and

Aluminium –

 

   

    

          

 

·         Both Be and Al are obtained by the electrolysis of their compounds in presence of a fluoride.

·         Both become passive by conc. HNO₃ .

·         Both form covalent compounds due to small size and high charge density of their atoms.

·         Their salts are hydrolysed by water Their salts are hydrolysed by water