By: Farhan Hameed

The periodic table organizes the elements in a particular way. A great deal of information about an element can be gathered from its position in the period table.

For example, we can predict with reasonably good accuracy the physical and chemical properties of the element. We can also predict what other elements a particular element will react with chemically.

Understanding the organization and plan of the periodic table will help us to obtain basic information about each of the 118 known elements.

In 1869, a Russian chemist called Mendeleev published a periodic table , he realized that the physical and chemical properties of elements were related to their atomic mass in a 'periodic' way, so that groups of elements with similar properties fell into vertical columns in his table.

Position of Hydrogen

The position of hydrogen was not correctly defined. It was placed in Group I although its properties resembled both the Group I elements (the alkali metals) and the group VII elements (the halogens).

Grouping of Some Elements

In some cases Mendeleev placed elements according to their similarities in properties and not in increasing order of their atomic masses, while some dissimilar elements were grouped together. Thus, the position of these elements was not justified. For example, cobalt (at. mass 58.9) was placed before nickel (at. mass 58.6); copper and mercury are similar in their properties but were placed separately. Copper was placed in group I although it did not resemble the elements of this group.

Anomalous Pair

In certain pairs of elements like, Ar (40) and K (39); Co (58.9) and Ni (58.6); Te (127.6) and I (126.9) the arrangement was not justified. For example, argon was placed before potassium whereas its atomic mass is more than potassium.

Isotopes

Isotopes are atoms of the same element having different atomic mass but same atomic number. For e.g., there are three isotopes of hydrogen with atomic mass 1, 2, and 3. According to Mendeleev's periodic table these should be placed at three separate places. However isotopes have not been given separate places in the periodic table.

Moseley's Periodic Table

Using atomic number instead of atomic mass as the organizing principle was first proposed by the British chemist Henry Moseleyin 1913, and it solved anomalies that seem in Mendeleev’s periodic table.

Modern Periodic law states as,

“The properties of elements are the periodic function of their atomic number not atomic masses”

GroupsVerticals columns in periodic table , it is 18 in

number.

PeriodsHorizontal rows in periodic table, it is 7 in number.

Groups

Sub Group A (Representative

Elements)

S-Block

P-Block

Sub Group B (Transition Elements)

D-Block

F-Block

S-Block (groups)

I-A (Alkali family)

II-A (Alkaline earth

metals)

P-Block (groups)

III-A (Boron family)

IV-A (Carbon family)

V-A (Nitrogen

family)

VI-A (Oxygen family)

VII-A (Halogens)

VIII- A (Noble gases)

D-block called Outer Transition Elements.

F-Block

Lanthanide series

Actinide series

(14 Elements)

Elements which have small no. of e- in there valence

shall.

All s , d and f block elements and few of p-block are metals.

Elements which have large no. of e- in there valence

shall.

Most p-block elements are non metals.

Metals and non-metals are separated by a heavy steep diagonal line, which physical appearance like metals some non-metallic properties as well.