Alum

Alums : Alums are the double salt (ionize in water) having general formula------

                           M2’SO4 M2’’’(SO4 )3.24H2O 

where,     

              M’ = mono-valent metal ions (like Na+,K+, Rb+ etc.)

             M’ =  non-metal ion (like Cs+, (NH4)+ etc.)
            M’’’ = Trivalent metal ions (like Al+3, Fe+3, Cu+3, Cr+3 etc.)

examples:-   K2SO4 .Al2(SO4)3.24H2O              Potash Alum.

                    Na2SO4 .Al2(SO4)3.24H2O            Soda Alum.

                   K2SO4 .Fe2(SO4)3.24H2O               Ferric Alum.

                   Na2SO4 .Cr2(SO4)

3.24H2O             Chrome alum.

            

               If M’’’ = Al, then name according to M’.
              If M’’’ = other than Al, then name according to M’’’.

Properties of Alums :

•  Alums are the white crystalline solid generally used to stop bleeding of small cuts.
• If M’ is replaced by M’’ like Zn+2, Cu+2, Fe+2 etc, then the alums are called as Pseudo alums.
  Exam: -     M’’SO4.M2’’’(SO4 )3.24H2O            Pseudo alums
                   Zn SO4.Al2(SO4 )3.24H2O                Pseudo alums.
•  Na2SO4 .Al2(SO4)3.24H2O + Heat → 
  Na2SO4 .Al2(SO4)3  
  + 24H2O

                                                                                            (burnt alum)

• Aqueous solution of alums are acidic in nature.

                                                                                       https://youtu.be/O3D2belxKBs

Properties of 'p' block elements

Properties of 'p' block elements :

• p-block consist of six groups from group 13 to group 18.
• General electronic configuration of p-block elements are ns2 np1-6  .
• It consist of metal, non-metals, metalloid and noble gases.
• Group 17th elements have the highest electronegativity among the periodic table.
• Group 17th elements are called as halogens.
• Group 18th elements are called as zero group elements because they neither gain electrons nor loose them.
• Group 18th elements are also called as noble gas or inert gas because they are non-reactive except xenon.
• Noble gases has highest Ionisation enthalpy and Positive electron gain enthalpy.
• Extreme right elements of periodic table except noble gases, act as good oxidising agent.

    Group 13            group 14            Group15             Group16            Group17               Group18

         B                           C                            N                       O                     F                          He

         Al                          Si                           P                        S                    Cl                          Ne

         Ga                        Ge                         As                      Se                   Br                          Ar

         In                          Sn                         Sb                      Te                   I                             Kr

        Th                          Pb                         Bi                      Po                 At                           Xe

                                                                                                                                                 Rn

                                                                                                         https://youtu.be/O3D2belxKBs

                                                                                                                                                                                                                                                                                                      

Properties of 's' block elements

Properties of 's' block elements :

• s-block consist of two groups, group I and II.
• General electronic configuration of s-block is ns1-2  .
• Group I elements are called as Alkali metals.
• Group II elements are called as Alkaline earth metals.
• They act as good reducing agents.
• They have high electropositivity as compared to p-block and d-block.
• Because of high electropositivity, sodium is kept in kerosine.
• Lithium is the most hardest element in the group I.
• Lithium shows diagonal relationship with magnesium.
• Lithium and Magnesium both are deliquescent or hygroscopic (absorbs water molecules from atmosphere) in nature.
• Lithium and Sodium forms oxide, Potassium forms peroxide and Rubidium,Cesium forms superoxide along with peroxide and oxide on reacting with oxygen.
• Lithium and Berillium forms covalent bond on reacting with halogens whereas rest of the elements forms ionic bond.

                             

                                                                                      https://youtu.be/O3D2belxKBs

Inert paired effect

Inert paired effect : It is the non participation of s-pair of electron in the bond formation due to poor screening or shielding of d and f orbitals.

Consequence of inert paired effect :

1) Due to inert paired effect lower oxidation state of elements of group of "p" block becomes more stable.

exam:-In group 13, +1 oxidation state becomes more stable in Indium and Thallium due to inert paired effect.

2) Due to inert paired effect f-block shows lanthanoid and actinoid contraction.

                                                                                https://youtu.be/O3D2belxKBs

Molecular orbital theory (MOT)

Molecular orbital theory :Postulates of this theory are--

• Atoms combine to form molecules and their atomic orbitals also combines to form molecular orbitals.
• Just like electrons are present in an atomic orbitals of an atom similarly in a molecule electrons are present in its molecular orbitals.
• The atomic orbitals of same energy and similar symmetry combines to form molecular orbitals.
• Atomic orbital is mono centric due to one nucleus centre whereas, molecular orbital s are poly centric.
• The number of molecular orbitals forms are equal in number of combining orbitals.
• Two atomic orbitals combine to form one as BMO (bonding molecular orbital) and other as AMO (anti bonding molecular orbital).
• BMO has more stability and less energy than AMO.
• Electrons in molecular orbitals are filled according to Auf-bau's principle, Hund's rule and Pauli's exclusion principle.

                                                                                          https://youtu.be/O3D2belxKBs

Fajan rule

Fajan's rule : 1) Greater the charge on anion or cation, greater is the polarasibility of anion and greater is the polarising power of cation.

2) Smaller is the size of cation, greater is its polarising power.

3) Greater is the size of anion, greater is its polarasibility.

4) Greater polarising power and greater polarasibility induces higher non polar character in an ionic bond.  

                                                                       https://youtu.be/O3D2belxKBs

Spectrum

Spectrum : The collection of waves of different frequency or wavelength in increasing or decreasing order of their wavelength or frequency is called as spectrum.

Depending on nature waves are of two type:

a) Continuous spectrum : A spectrum in which different regions are not separated by dark lines are called as continuous spectrum.

b) Line spectrum : The spectrum in which different regions are separated by dark fine lines are called as line spectrum.

Line spectrum are also of two type:

1) Atom emission spectrum : It is obtained from the radiation  emitted from atom in its excited state (higher energy state of atom).

The radiation of excited atom are made to fall on prism so that a line emission spectrum of an atom is obtained.

2) Atom absorption spectrum :It is obtained from an atom in its ground state (lower most energy state).

When a white light is passed through an atom and it is taken up to prism after passing through an atom then it splits up and form a line absorption spectrum of  an atom.

                                                                               https://youtu.be/O3D2belxKBs