Modern Periodic Table

Modern Periodic Table

Scientist Henry Moseley proved that the atomic number of an element is the basic property and not the atomic mass. Thus atomic number forms the foundation for the Modern Periodic Table. The atomic number of an element is the number of protons in its nucleus. Elements arranged in ascending order of their atomic number has the same valence electrons repeated at regular intervals, thus causing periodicity.

In this topic, you will learn about modern periodic law and long form of periodic table.

Modern Periodic Law

Moseley modified Mendeleev’s periodic law to form the modern periodic law – The physical and chemical properties of elements are the periodic function of their atomic numbers.

Atomic number is the total number of protons present in the nucleus and is responsible for the chemical properties of the element. When elements are arranged according to increasing atomic number, there is periodicity in the number of valence electrons and corresponding periodicity in chemical properties.

The cause of periodicity is the recurrence of similar electronic configuration.

Long form of periodic table

Valency increases from 1-4 and then decreases from 4-0 across the period.

Valency remains the same down the group.

Ionisation potential increases down the group.

Atomic size increases down the group due to addition of a new shell.

Electron affinity decreases down the group.

Metallic nature and basic nature of oxides decreases across the period.