Preparation of Sodium by Down's cell

In down's cell sodium is prepared by electrolysis of molten (fused) sodium chloride some Cacl2 is added to low the melting point of Nacl from 801 c to 600 c.The cell consists of n iron vessel. A large block of graphite acts as an anode. Above the anode there is an iron dome for the collection of chlorine.

The cathode is made of iron or copper. It is separated from anode by iron gauze screen. When electric current passes through molten Nacl, following reactions take place.

                                                Nacl------>  Na+ + cl-

                                                Na+ + e- -------> Na ( at cathode)

                                                2cl- -----------> Cl2 + 2e- (at anode)

The sodium collects over cathode and chlorine collects over anode. They are taken out from different holes. This process has following advantages.

(1) The metallic fog is not produced. 

(2) Liquid sodium is collected at 600c.

(3) It gives 99.9% pure sodium.

(4) Material of the cell is not attacked by the products formed during electrolysis.

Peculiar behaviour of Beryllium

(Differences between Be and other members)

1:- Be has small size and  high electronegativity as compered to other members of its family.
2:- BE has high melting and boiling point than other members of its family(group!!A)
3:- Be is much harder than other members of its own family. Be is as hard as iron and can scratch glass.
4:- BE reacts with alkalies but other members of its family do not
                                  Be +2Naoh----------> Na2beo2+ H2
                                                                        (sodium berryllate)
5:- Be does not oxidize completely due to formation of BeO coating.
6:- Be cannot reduce water completely but other alkali earth metals act as powerful reducing agents for water.

 General behavior  of alkali metals

A substance which can lose electron is called reducing agent. Alkali metals are strong reducing agent due to Low ionization energies. They are highly electropositive and can form halides.

The modern periodic table

6th period:- The 6th period contain 32 elements . It is first very long period it contain 8 normal elements, 10 transition elements and 14 inner transition elements called follow lanthanum are called landslides . They start from cerium t lutetium. They have inner transition or rare earth elements.

7th period:- The 7th period is the last period in periodic table. It is incomplete so for. It is second very long period . It contain 2 normal elements, 10 transition elements and 14 inner transition elements. A set of fourteen elements which follow Actinium are called Actinides. They start thorium to lawrencium. The elements in the Lanthanum and actinium series are called inner transition or rare earth elements.

The Modern Periodic table

The modern periodic table is based upon modern periodic law. This law states, " if elements are arranged in ascending order of their atomic number, their chemical properties repeat in a periodic manner." in modern periodic table all elements are arranged in ascending order of their atomic number/ Some essential features of modern periodic table are given below.

Groups:- The vertical columns of elements in periodic table are called groups. There are eight groups. They are represented by Roman numbers 1 to 8. Each group is divided into two sub-groups a and b. The sub-groups B contains transition elements . The elements of A group have similar properties.

Periods:- The horizontal rows of elements in periodic table are called periods. There are seven periods .They are represented by Arabic numbers 1 to 7.

1st period:- First period contains two elements, They are hydrogen and Helium . It is the shortest period.

2nd and 3rd periods:- Second and third periods contain eight elements each. They are called short periods. The elements of these periods are normal elements and belong to A sub-groups. In these periods the properties of every eight elements are similar to the first element. For example, Lithium of 2nd period is similar to sodium of 3rd period. Similarly Boron and Aluminium both show oxidation state of +3.

4th and 5th periods:- The 4th and 5th periods contain eighteen elements each. They are called long periods. There are eight normal elements and ten transition elements in these periods. In these periods properties repeat after 18 elements For example19k is similar to 37 rb.

The Modern Periodic Table

     The modern periodic table is based upon modern periodic law. This law states, “if elements are arranged in ascending order of their atomic number. Their chemical properties repeat in a periodic manner.” In modern periodic table all elements are arranged in ascending order of their atomic number. Some essential feature of modern periodic table is given below.

Groups: -     The vertical columns of elements in periodic table are called groups. There are eight groups. They are represented by Roman numbers 1 to 8. Each group is divided into two sub-groups A and B. The Sub-groups A contains typical or normal elements. The sub-groups B contain transition elements. There are seven periodic table are called periods. They are represented by Arabic numbers 1 to 7.

Improvement in Mendeleev's periodic table ( Modern periodic Law)

 In 1913 , Mosley discovered atomic number. After the discovery of atomic number the periodic table was improved. This improvement id based upon Modern periodic Law. This law states,
                                                                                                          "If the elements are arranged in ascending order of their atomic numbers, their chemical properties repeat in a periodic manner."
By modern periodic law, confusions (defects) in Mendeleev's  table are removed.

Periodic classification of elements and periodicity

Defect of Mendeleev's table:-
   (1) Mendeleev's table does not explain structure of atoms
   (2) It does bit clear the position of isotopes.
   (3) In this table position of K, Ar, and Ni. Co is against the periodic law.
   (4) In Mendeleev's table many position were vacant. These position were for unknown elements. e.g.     Germanium (GE) Gallium (GA).
   (5) ZN, Cd , Hg and alkaline earth metals have very different properties. They are placed in dame group. It is against the periodic law
   (6) In this table the position of Lanthanides and Actinides is against the periodic law.