Modern Periodic Law

Modern Periodic Law

The modern periodic table is developed after the periodic law and a periodic table given by Mendeleev. In the latter part of 18th century, Mendeleev made his periodic table. Scientists did not know about the internal structure of atom back then. The development of various atomic models and advances in quantum theory revealed that atomic number is the most basic property of a chemical element. This led to the modification of Mendeleev’s periodic law, which is today called as modern periodic law.

Modern Periodic law

The modern Periodic law can be stated as:

the physical and chemical properties of the elements are periodic functions of their atomic numbers”.

Atomic number is equal to the number of electrons or protons in a neutral atom. After knowing the fundamental unit of elements, scientists now had a clear idea about quantum numbers and electronic configuration of elements in the periodic table. After knowing the periodic law, chemists noticed that there is an analogy between the 94 naturally occurring chemical elements. This analogy made people more curious about the chemistry of these elements. Scientists made various artificial elements. A new periodic table was developed based on the modern periodic law by modifying the Mendeleev’s periodic table.

The Modern periodic table:

The present form of a periodic table which is widely used across the globe is the long form of the periodic table. In this form of a periodic table, the horizontal rows are called periods and the vertical columns are known as the groups.

Groups consist of elements that have similar outer shell electronic configuration in their atoms. Previously the groups were named as IA,…VIIIA, VIII, IB…VIIB and 0. But now they are named as 1, 2, 3…18. In the modern periodic table, periods are the seven horizontal rows. Principle quantum number ‘n’ decides the period of the element. Principle quantum number (n) is one of the four quantum numbers (n, l, m, and s). It tells us about the principle electron shell. For example, if n= 3, then it indicates the principle shell as 3.

Classification of the elements in the periodic table:

Classification of the elements in the periodic table can be done in four ways on the basis of their electronic configurations:

  1. Noble gas elements:

Elements of group 18 of the modern periodic table are considered a noble gas. Electronic configuration of the first element (helium) of this group is 1s2. Rest all the elements (neon, argon, krypton, xenon, and radon) have their outer shell electronic configuration is ns2np6. As the octet of these elements is complete, hence they are highly stable elements.

  1. Representative elements:

S-lock and P-block elements come under the category of representative elements. Elements in group 1 and 2 are known as the s – block elements (elements with 1s2and 2s2 outermost configuration). Group 13-17 are known as the p-block elements (outermost configuration varies from ns2np1 to ns2np5).

  1. Transition elements:

Elements which belong to group 3 to 12 and have their outer shell electronic configuration as (n-1)d1-10ns1-2 are referred to as transition elements. These elements are also known as the d-block elements.

  1. Inner transition elements:

Lanthanides and actinides series which falls at the bottom of the periodic table comes under the category of inner transition elements. In these elements the 4f and 5f orbitals are partially filled, rendering them special properties.

This is just a brief description of the periodic table and the classification of elements. To know more about it, register with Byju’s & download Byju’s – the learning app.

Learn more about Electron Gain Enthalpy here:

If you still have doubts regarding the periodic law and would like to learn more, check out our Introduction to the Periodic Table for detailed clarification.

Practise This Question

Atomic mass of X and Z is 20 and 40 respectively. If X, Y and Z is Dobereiner's Triad. What can be the atomic number of Y?