chemistry

LONG FORM OF PERIODIC TABLE

It is based on modern periodic law or Mosley’s periodic law. It states that “the physical and chemical properties of elements are the periodic functions of their atomic numbers or electronic configuration.

The properties are repeated after regular intervals of time when the elements are arranged in the increasing order of their atomic numbers.

Neil’s Bohr constructed the modern periodic table based on the electronic configuration of the elements.

It is a graphical representation of Aufbau principle.

The vertical columns are called groups and the horizontal rows are called periods.

There are altogether 18 groups and 7 periods in the long form (or) extended form of periodic table. Elements are arranged in the increasing order of their atomic numbers.

From left to right the atomic number increases by one unit.

The electron which differentiates an element from the preceding element is called the differentiating electron.

The differentiating electron is the last coming electron of that element.

In each period, in the first element the differentiating electron enters into s-orbital and in the last element the differentiating electron enters into p-orbital.

The last element of the period completes the octet by attaining the stable electronic configuration ns²np⁶.

Thus every period start with the filling of valence s-orbital and ends with the complete filling of s and p-orbitals of valence shell.

First period contains only two elements H(1s¹) and He(1s²) and it is called very short period. Second period contains 8 elements and it is called 1^stshort period.

Third period also contains 8 elements and it is called 2^nd short period. The first 3 periods are discontinuous periods.

4^thperiod contains 18 elements and it is called 1^stlong period.

5^thperiod also contains 18 elements and it is called 2^ndlong period. Sixth period is the longest period containing 32 elements.

Elements do not exhibit horizontal similarities as they differ in the configuration.

Some periods are broken and some periods are extended to accommodate transition elements.

14 elements each of 6^thand 7^th periods have been separately placed at the bottom of table to maintain uniformity and effectiveness.

2^nd period elements are Bridge elements due to their diagonal relationship.

3^rdperiod elements are called typical elements as they represent the properties of below elements in the respective groups.

GROUPS :

There are 18 groups.

They are designated as group A and Group B except VIII and '0' groups. VIII group consists of 3 vertical rows or 3 groups.

'0' group consists of Noble gases.

Groups ‘A’ consists of representative elements and groups ‘B’ and VIII group consists of transition elements.

Elements belonging to group will exhibit similar properties due to similar valence shell configuration.

The elements which exhibit both vertical and horizontal similarities are transition elements. The number of electrons in valence shell is equal to the group number.

The seventh period is incomplete and has about 20 elements.