Periodic Table

Understanding Periodic Table: A shopkeeper dealing in different items say stationary, cosmetics, confectionery, etc. place things of one type at one place. In the library, books on one subject are placed in one almirah. This is done for convenience and to make things easy and simple.

Similarly, a total of 118 natural and synthetic elements are known. These elements have different physical and chemical properties and they combine with one another to form millions of compounds each having different properties. It becomes difficult to study the properties of elements and their compounds individually because of their vast number. So there is a need of a modern long form of table.

What is Periodic Table?

Periodic Table is one in which all the known elements have been arranged on the basis of their properties in such a way that elements with similar properties have been grouped together in the same vertical column and dissimilar elements are separated from one another.

Development of the Periodic Table

 Attempts have been made from early times to develop and classify the known elements so as to make the study of chemistry simpler, systematic and interesting. This leads an easy way to study properties of elements and their compounds. Thus, instead of studying each of 118 elements individually, it is much more convenient to study them into a few broad groups.

How to Read the Periodic Table?

We can study the properties of elements in two ways: one divide it into blocks and second considering periods and groups. The following is a study with groups and periods.


First period

This period is the shortest period. The first period has 2 elements hydrogen (1s1) and helium (1s2) only. In their case, the first shell K is completed. Here n = 1.

Second period

It contains the eight elements and termed as short period.The second period starts with n = 2, the first member is lithium and the shell (L) is completed at Neon.

Third period

Similarly, the third period (n = 3) starts with sodium (Z=11) and is completed at argon (Z=18). This period also contains the 8 elements.It is also called as a short period.

Fourth period

This period called as long period. It contains 18 elements with Z = 19 to 36. The fourth period (n = 4) starts with potassium and ends with Krypton but has 10 more elements than the 3rd period. It has total 18 elements.

Fifth period

The fifth period (n = 5) is similar to the fourth period and has 18 elements in all. It starts with rubidium and ends with xenon.

Sixth period

The sixth period (n = 6) has 32 elements in which the filling up of electrons takes place in 6s, 4f. 5d and 6 p orbitals respectively from Cs to Rn. Filling up of the 4f orbitals begins with cerium (Z = 58) and ends at lutetium (Z = 71) to give the first f transition series called Lanthanide series.

Seventh period

This seventh period (n = 7) would be similar to the sixth period but is incomplete and contains only 19 elements from Fr to Ha. It includes most of the man-made radioactive elements. Filling of 5 f orbitals after actinium (Z = 89) gives the second f transition series known as the actinide series.


The vertical columns are called as groups. There are 18 groups in total.

For the knowledge of Groups read the following subtopic:

Electronegativity Periodic Table

  • The value of electronegativity found to be maximum in fluorine and minimum in cesium.
  • Electronegativity is generally measured with the help of the Pauling scale.
  • Electronegativity has a great impact on the type of bond chemical bonding.
  •  Read more: Electronegativity.

Metals on the Periodic Table

Except for p block, the s, d and f block elements in the long form table are metals. Their metallic character decrease moving left to right and increases moving top to down. The elements are present on the left side are metals.  

Modern Periodic Table

In the year 1913, an English physicist, Henry Moseley, a young physicist from England, studied the frequencies of the X-rays which were emitted when certain metals were bombarded with high-speed electrons. He found that in all the cases, the square root of the frequency (v) was directly proportional to the atomic number of the atom of the metal.

These studies led Moseley to believe that instead of atomic mass, atomic number is the fundamental property of an element. In the light of the above observations, Moseley gave the modern periodic law which states that:

Physical and chemical properties of the elements are the periodic function of their atomic number.

The elements with a different electronic arrangement of the atoms possess different chemical properties. As the number of electrons in an atom is given by the atomic number and not by the mass number, therefore, the atomic number should form the basis of the classification of the elements in the long form of table and not atomic mass as predicted by Mendeleev.

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