Class 10 Periodic Classification of Elements Notes

Class 10 Periodic Classification of Elements Notes

These are CBSE textbook notes of chapter 5, class 10 science. These “Periodic Classification of Elements” notes will help you learn and revise this unit.

Why Do We Classify Elements?

Studying the chemistry of each element would be very time-consuming and difficult without the classification of elements. As a result, elements and their compounds are divided into groups and periods to make their study easier and more systematic.

Early Attempts at the Classification of Elements

The initial attempts to categorise elements were based on the chemical and physical properties that researchers had observed. We contrasted a few reactions with well-known materials and components.

The weights of their atoms determined their placement. To classify the properties, they attempted to investigate the periodicity of the characteristics as the atomic weight increased.

The law of octaves then followed the law of triads. Doberneiner, Chancourtois, and Newlands created several tables in addition to proposing these laws.

The Earliest Models of Periodic Table

Dobereiner’s Trails

The middle element’s atomic mass was equal to the average of the atomic masses of the other two elements when the elements were listed in order of increasing atomic mass.

Mass of Atomic Element

Ca= 40.1

Sr= 87.6

Ba= 136.3

Limitations: From the elements known at the time, only three triads were recognised.

The relative mass of an element’s atom, measured against the mass of a carbon-12 atom divided by 12, is known as the element’s atomic mass.

The Octave Law of Newland Is based on an increase in elemental atomic mass.

The Law of Octaves states that every eighth element has properties that are similar to the first element when elements are arranged. For instance, sodium and lithium have similar properties.


  • Only applicable up to Calcium
  • New elements’ properties couldn’t fit in it
  • Sometimes, an element’s properties did not match those specified by its octave. For instance, Co and Ni were far away from Fe
  • Only the lighter elements followed the law

The Periodic Table of Mendeleev 

Mendeleev’s law of periodicity states that an element’s properties are a periodic function of its atomic mass.

The periodic table created by Mendeleev is based on the chemical makeup of elements. It has horizontal rows called “periods” and vertical columns called “groups.”

He concentrated on classifying the oxides and hydrides these elements produced. He put them in order based on their atomic masses. Not only the chemical but also the physical properties were found to repeat at regular intervals.

Mendeleev’s Periodic Table’s Achievements

  • Elements with related characteristics may be grouped.
  • There were some gaps for the undiscovered elements.
  • No order could be disturbed by the placement of noble gases.


  • The position of hydrogen is not fixed.
  • Isotopes don’t belong here.
  • There is no consistent trend in atomic mass.
  • Co was positioned before Ni.

The Periodic Table of Today

Henry Mosley presented modern periodic law in 1913.

A periodic function of an element’s atomic number determines its properties. The number of protons in the atom’s nucleus, indicated by the letter Z, is known as the atomic number. The modern periodic table has 18 vertical groups (columns) and 7 horizontal periods (rows). The number of valence electrons shared by all members of a group is one.

As we move down the group, there are more shells. Elements in a period have the same number of shells. Each period represents the filling of a fresh electronic shell. The number of elements arranged in a given period depends on how electrons are arranged in the different shells.

The formula, where n is the number of the given shell, determines the maximum number of electrons that can fit in a shell. For instance, K shell – 2 (1) = 2 elements in the first period. In the second period, L shell – 2 (2) = 8 elements.

The periodic table’s placement of an element provides information about its reactivity.

The Modern Periodic Table’s Trends

  • The number of valence electrons found in the outermost shells is known as valency. The value fluctuates over a period but is constant within a group.
  • Atomic size is defined as the radius of an atom.
  • As the nuclear charge increases, the size, or radius, of an atom shrinks as it moves from left to right along a period.
  • The atomic size increases down the group because new shells are being added as we go down the group.
  • Metallic Character: The term “Metallic Character” refers to an atom’s propensity to lose electrons
  • Because the effective nuclear charge increases and the tendency to lose electrons decreases, the metallic character decreases over time.
  • Because they frequently lose electrons while forming bonds, metals are electro-positive.
  • As the effective nuclear charge decreases, the metallic character increases down the group. Electro-negative materials are non-metals. They frequently pick up electrons to form bonds.
  • In the periodic table, metals are on the left side, while non-metals are on the right.
  • Semi-metals, also known as metalloids, are in the middle because they exhibit traits of both metals and non-metals.
  • The nature of metal oxides is basic, whereas the nature of non-metal oxides is acidic.
S. No. Property Variation

across period

Reason Variation along group Reason
1. Atomic weight Decreases Because of an increase in nuclear charge Increase Because of the addition of new shells, the distance between the outermost electron and the nucleus grows.
2. Characteristics of Metal Decreases Due to an increase In an effective nuclear charge, the tendency to lose valence electrons decreases. Increases in Valence electrons suffer from a decrease in their effective nuclear charge. The tendency to lose electrons (metallic character) grows.
3. Character (electro-negativity) is enhanced by non-metallic compounds. Increase The tendency to gain electrons increases as the effective nuclear charge increases. Decreases The tendency to gain electrons decreases as the effective nuclear charge of the valence electron decreases (due to the addition of a new shell).

CBSE Class10 Revision Notes and Key Points

Use these Class 10 Notes for the periodic classification of elements to review the entire syllabus on exam days. CBSE quick revision notes for Class 10 Science, Chemistry, Math, Biology, and other subjects are very helpful. The revision notes cover every significant formula and idea presented in the chapter. These notes will undoubtedly save you time on those hectic exam days.


An element’s position on the periodic table reveals much more about it than just how many protons are in its nucleus. As we have seen, the periodic table also provides a wealth of knowledge regarding each element’s chemical and physical characteristics.

Frequently Asked Questions

1. When did Mendeleev create the periodic table?

Mendeleev created the periodic table in 1869.

2. Describe a halogen.

A halogen is a chemical element that reacts with a metal to produce salt.

3. What exactly is Electronegativity?

The propensity of an atom to draw electrons into a molecule is known as electronegativity. A complete transfer of an electron from one atom’s unfilled outer shell to another’s unfilled shell frequently results from significant changes in electronegativity between the atoms in a particular molecule.