QUESTION

outline factors that enable elements to have diagonal similarities

A. similar electronegativity
B. similar atomic and ionic sizes.
C. have ions  with similar polarization power.

ANOMALOUS BEHAVIOUR OF THE FIRST ELEMENT IN A GROUP OF THE PERIODIC TABLE

The first element in every group  of the period show some  properties  which are not  shown  to other elements in the respective group .The  element is said  to show anomalous behavior when its properties differ with those  of  the rest  group member. The anomalous behavior   of the first element in a group is due to the following factors,

A.    The first  element in a group has the smallest  atomic  and  ionic size  when compared with the rest group  members

B.     The first  element in a group has the highest ionization energy

C.     The first element in a group has the highest electronegativity

D.    The first element in a group has the higher electronic  affinity

ANOMALOUS BEHAVIOUR OF LITHIUM 

                 I.   Lithium  forms covalent  compounds  while  other alkali  metals  form ionic  compound  example  LiCl is  a covalence  compound while NaCl  is ionic

                II.   Lithium reacts  with nitrogen  gas on heating to form ionic nitride  while other alkali metals do not react

                       

                 III.   Lithium reacts slowly with cold water while other alkali metals react vigorously

                  IV.    Lithium forms  hydrated chloride while the rest group member  form anhydrous chloride  example LiCl.2H₂O  and NaCl (Li can polarize water due to high polarizing power)

                   V.   When burnt in air ,lithium gives the monoxide while other alkali  metals form peroxide and super oxide

              

                                              Lithium monoxide

               

                                                                  Sodium peroxide

Potassium peroxide

                   VI.    Lithium  does not  form acetylide with ethyne (acetylene ) while other alkali metals form acetylide with ethyne

         

            

                 VII.   Lithium is only alkali metal whose salts may undergo hydrolysis

                   

                  

                VIII.   The hydroxides of lithium decomposes on heating to monoxide and water while hydroxide of other alkali metals sublime undecomposed

               

               

                   IX.    Lithium nitrate  decomposes on heating into Lithium monoxide, nitrogen dioxide and oxygen  while the nitrates of other alkali metals  decompose  into  nitrites  and oxygen.

                 

                 

                      

                    X.   Lithium carbonate  decomposes gently  heating  into monoxide  and carbon dioxide  while  the carbonates  of other  alkali metals  are stable .They decompose at higher temperature.

              e.g.   

                       

                   XI.     Lithium  hydroxide  is less soluble in water  and hence a much weak base than sodium  hydroxide a and potassium  hydroxide

                 XII.     Lithium  chloride  is deliquescent  while chloride  at the  rest group  members aren’t deliquescent

                XIII.    Lithium  sulphate  do not form alums  while  the sulphate of the  rest group form alums

ANOMALOUS BEHAVIOUR OF BERYLIUM

      1.  Beryllium  react  with concentrated  solution  of alkali to form hydroxo-complexes and hydrogen gas while other alkaline earth metal do not react

          E.g. 

                  

      2.  The  oxides and hydroxides of beryllium are amphoteric while those of other alkaline earth metals are basic

      3.  Beryllium chlorides hydrolyze in water while the chlorides of the rest group members do not.

        BeCl₂ + H₂O → Be(OH)₂ + 2HCl   (Hydrolysis)

       

      4.  Beryllium chloride dimerize in vapour state while the chloride of the rest group member do not dimerize.

          Beryllium chloride Dimer

      5.   Beryllium form fluoro-complexes while other alkali earth metals do not.

      6.  The chloride of beryllium readily dissolved in organic solvents while the chlorides of other alkali earth metals do not readily dissolved in organic solvents.

      7.   Beryllium  do not react with water or steam while other  group members can react with either cold or boiling water or steam.

      8.  Beryllium  oxide do not react with water while the oxide of the rest group members react with  water to form hydroxide.

          

       _9.    Beryllium  do not react with either dilute or concentrated  nitric acid  while the  rest  group  member react with both  dilute  and concentrated

     10.  Beryllium carbide hydrolyses  in  water  to form  methane  while  the carbides of other  group  members  give ethyne

       ()

CaC_2(s) + 2H₂O_(cold) → Ca(OH)₂ + H – C ≡ C – H  ((C^– = C^–)^-2 Oxidation state)

      11.  Beryllium chloride fumes in moist air while chloride of the rest   group members do not.

                 

                                  (From air)

The fumes   are due   to hydrolysis of  in water where    is given out.