Page 1 - 3. Lesson Note Ch-5 MODERN PERIODIC TABLE

SAI International School
Class-X

Subject - Chemistry
Topic- Periodic Classification
Sub topic- Modern Periodic Classification

(Intro. & Description)

LESSON NOTES

➢ Modern Periodic Classification-
In the modern periodic table, elements are arranged in order of their-

a. increasing atomic numbers.
b. similarity in chemical properties.

Atomic number is considered to be a more fundamental property of an element as
compared to its atomic mass.

Reason- Atomic number gives us the number of protons & electrons in an element,
hence it also tells us the number of valence electrons, which is responsible for the
chemical properties of an element.

On arranging elements according to the increasing order of atomic numbers, they were
automatically arranged according to their gradual change in chemical properties.

So it was observed that elements with similar chemical properties were repeated at
regular intervals.

This lead to the framing of The Modern Periodic Law-
This Law states that “Properties of elements are a periodic function of their atomic
numbers.

On doing so, it was observed that the anomalies of Mendeleev’s periodic table were
removed.

Mendeleev’s Periodic table Modern Periodic table
1. Position of hydrogen was not 1.Hydrogen is placed in the group of
ascertained, as it had properties Alkalies.
similar to Alkali metals and
Halogens

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