A periodic table is a
table that contains an arrangement of chemical elements.
There are more than 100 chemical elements
(118) identified so far in the world. So it is difficult to study each of
them, understand them and remember them and their physical and
chemical properties. Also it is difficult to discuss with other scientists
and experts with out a common platform.
The periodic table enlists the chemical elements
in a logical order of atomic number. Atomic number is the number of
protons or the number of electrons in an atom in that element.
A row is called a period. The atomic
number increases in a period as you move from left to right and increases as
you move from top to bottom. A column is called a group. The
elements in a group have similar physical and chemical characteristics.
The group number increases from 1 to 18 as you move from left to right in
The periodic table took a number of years to
develop. It was Mendeleev who published the first periodic table in 1869.
The current standard form of the table is attributed to HG Deming.
Seaborg published the placement of actinide elements in f block and
synthesized them. He won the Nobel prize for that in 1951.
The first element in the table is Hydrogen (N =
1). The last one is Unanoctium (N=118). The s block (groups 1 & 2) and p
block (groups 13 to 18) are most important. We study them in detail. The
remaining are more complicated and studied in advanced degrees. The
elements in between s & p block are called d block and those below d block
are called f block.
The atomic weight increases from left to right
and from top to bottom. Atomic number increases by 2 for the second period,
and by 8 for the 2nd and 3rd. It increases by 18 for the rest.
The elements in the rightmost 18 th
group are called the inert or noble gases.
The chemical properties are studied comparing
one element with another in the same group or period. Atomic radius increases
in a group from top to bottom. Atomic radius decreases from left to right in a
period. Similarly metallic charactr, eletron affinity etc are studied.
There are other forms of periodic table made by
different scientists in two dimensions, three dimensions and using colour also
in a four dimensional table. There are also extensions with g block consisting
of newly synthesized elements. A spiral table developed by T Benfy in
1960 with Hydrogen at the center is a popular one.