Periodic Classification of Elements Class 10 Notes

Periodic Classification of Elements Class 10 Notes: See the CBSE Class 10 Science Notes for Chapter 5 – Periodic Classification of Materials for Quick Revision before the 2021 Board Exam. These notes are in accordance with the revised CBSE Class 10 Science syllabus. Everything is explained in a simple way. It will take about 10-15 minutes to revise the whole chapter with these quick revision notes. Periodic Classification of Elements 10 Notes – CBSE Class 10 Science Chapter 5 I will discuss in detail the chapter on ‘Periodic Classification of Elements’ with the meaning of difficult words.

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CBSE Class 10 Science Notes Chapter 5 Periodic Classification of Elements – Periodic Classification of Elements Class 10 Notes

“Periodic table is a table method of displaying elements in such a way that elements with similar properties occur in the same vertical column or group”.

Previous attempts at classification of elements: The Eighteenth Amendment of the Debreiners Triads, Newland.
I will first discuss the Debreiners Triads and the Eighth Law of Newland.

Dobreiner Trades: This classification is based on atomic mass. According to this, when elements are arranged to increase the mass of an atom, groups of three elements with the same properties are found. The atomic mass of the middle element of the triad is equal to the mean of the atomic mass of the other two elements.
E.g., Li (6.9), Na (23), K (39).



  1. The properties of the material were the same in each triad.
  2. The atomic mass of the middle element was roughly the average of the atomic masses of the other two elements.

Limitations of Dobereiner’s Triads: Dobreiner could only identify three trios from the material known at the time. Thus, he fails to arrange all known elements into a trilogy, even possessing the same properties.

Octave’s formula in Newland: According to this ‘when elements are placed in order of increasing atomic masses, the physical and chemical properties of every 8th element are a repetition of the properties of the first element.’

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The form of Newland’s octaves is given in the following table:

Limitations of Newt’s Octave law:

  1. Newland’s Octave law only applied to calcium, since every eighth element after calcium did not have the same properties as the first.
  2. The properties of the later discovered elements do not conform to Octave’s law.
  3. In some cases, Newlands adjusts two elements in the same slot to fit its table.
  4. He also grouped different elements under the same slot.


  1. It contained everything from hydrogen to thorium.
  2. The characteristics of each eighth element were the same as the first element.

Example: Cobalt and nickel are in the same slot and placed in the same column as fluorine, chlorine, and bromine which have different properties from these elements.

Mendeleev’s Periodic Table: It is in accordance with the fact that the bodily and chemical houses of the elements are the periodic functions in their atomic plenty. This reality is named Mendeleev’s Periodic Law.

Features of Mendeleev’s Periodic Table:

● Twelve horizontal rows, that have been condensed to 7, are referred to as periods.

● Eight vertical columns are referred to as groups.

● Groups I to VII are subdivided into A and B subgroups.

● Group VIII doesn’t have any subgroups and incorporates three parts in each and every row.

● Elements in a similar team show off identical properties.

Achievements of Mendeleev’s Periodic Table:

1. A systematic study of elements: Elements with similar properties were grouped together, which made the study of their chemical and physical properties easier.
2. Correction of atomic masses: Placement of elements in Mendeleev’s periodic table helped in correcting the atomic masses of certain elements. For example, the atomic mass of beryllium was corrected from 13.5 to 9. Similarly, atomic masses of indium, gold, platinum, etc., were also corrected.
3. Prediction of properties of yet-to-be-discovered elements: Eka-boron, eka-aluminum, and eka-silicon were the names given to yet-to-be-discovered elements. The properties of these elements could be predicted accurately from the elements that belonged to the same group. These elements, when discovered were named scandium, gallium, and germanium, respectively.
4. Placement of noble gases: When discovered, they were placed easily in a new group called zero groups of Mendeleev’s table, without disturbing the existing order.

The limitations of Mendeleev’s periodic table:

(a) No fixed position for hydrogen: No correct place of the hydrogen atom was once in Mendeleev’s periodic desk. Example: Position of hydrogen with alkali metals and halogens (17th crew).

(b) No place for isotopes: The position of isotopes used is no longer decided. Example: Cl-35 and Cl-37.

(c) No regular development in atomic mass: Position of a few components with lower atomic masses ahead of upper atomic mass. Example: Ni-58.7 prior to Co-58.nine.

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Modern Periodic Table – Periodic Classification of Elements Class 10 Notes

This table is in keeping with the Modern Period Law which states that “The physical and chemical properties of elements are the periodic function of their atomic numbers.”

All The elements on this table have been arranged in order of accelerating atomic numbers. Elements in the Modern Periodic Table are organized in 18 vertical columns referred to as teams and 7 horizontal rows called periods.

Modern Periodic Law: In 1913, Henry Moseley showed that the atomic number of an element is a more fundamental property than its atomic mass.

The period in modern periodic table:

The elements present in the same period have the same number of shells which is equal to the number of periods.
Moving from left to right over a period of time, the number of electrons in the valence shell increases from one to eight while the number of shells remains the same.

Number of Elements in a Period:

The first duration incorporates the handiest two parts 1Hand2He and is known as the shortest length.

The 2d period (3Li to 10Ne) and the 3rd length (11Na to 18Ar) include 8 components each and are known as brief sessions.

The fourth duration (19okay to 36Kr) and the 5th duration (37Rb to 54Xe) accommodates 18 parts every and are called long periods.

The 6th duration contains 32 components (55Cs and 86Rn) and is sometimes called the longest duration. The 7th period is an incomplete length.

(After the hot discoveries of the brand new components and their addition to the periodic table, the 7th period is formally complete).

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Groups in Modern Periodic Table – Periodic Classification of Elements Class 10 Notes

The modern periodic table contains 18 vertical columns known as groups.

Group 1 elements are known as alkali metals.
Group 2 elements are known as alkaline earth metals.
Group 15 elements are known as pnicogens.
Group 16 elements are known as chalcogens.
Group 17 elements are known as halogens.
Group 18  elements are known as noble gases.

Alkali Metals: The elements in the first group, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr) are called alkali metals.
They were given the name because they all react with water to form alkalis.
The alkali metals are all shiny, soft, highly reactive solids at standard temperature and pressure and readily lose their outermost electron to form cations with charge +1.
Number of valence electrons = 1

Alkali Earth Metals include beryllium (Be) – group 2 elements ranging from radium (Ra). They are less reactive than alkali metals found as compounds.

Transition element: This includes elements of groups 3 to 11. They are named because they show a change in their properties from left to right, including an increase in atomic size, ionization energy, and electronegativity.

Internal conversion material: These are elements with similar properties, placed at the end of group 3 in periods 7 and 8. These are called lanthanide series which starts with 14 elements from lanthanum (La) – lutetium (Lu). Period 7 contains 14 components ranging from Actinium (AC) -Lorensium (LR).


The elements in the seventeenth group (F, Cl, Br, I, and As) are called halogens and exist as diatomic molecules. The symbol ‘X’ is often used generically to refer to any halogen.
They were given the name halogen, from the Greek words, Hal (“salt”) and gen (“to produce”), because they all produce a wide range of salts reacting with metals.
The halogens exist at room temperature in all three states of matter: Solid – Iodine, Astatine. Liquid – Bromine. Gas – Fluorine, Chlorine.
Number of valence electrons = 7

Classification of modern periodic tables: Modern stage tables are divided into metals, non-metals, and metallic materials.

Metal: Metals are electropositive because they form bonds by losing electrons. In the general case, oxides of metals are fundamental in nature.

Non-metallic: Non-metals are electronegative because they form bonds by gaining electrons.
In general, non-metallic oxides are acidic in nature.

Metals: Materials that show the properties of both metals and non-metals are called metals or semimetals. Such as boron, silicon, germanium, arsenic, antimony, tellurium, and polonium.

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Trends in Modern Periodic Tables:

i) Valence: Valency may be outlined because of the combining capacity of the atom of an element with atoms of different parts to be able to gain the stable configuration (i.e. 8 electrons within the valence shell. In some particular instances it is 2 electrons).

ii) Atomic size: Atomic size refers back to the radius of an atom. It is the distance between the center of the nucleus and the outermost shell of a remoted atom. In Period: On shifting from left to right in a length, atomic size decreases as a result of nuclear fee increases.

Example: Size of 2nd length components: Li > Be > B > C > N > O > F

iii) Metal character: It is the tendency of an atom to lose electrons. In Period: Along the length from left to right, metallic characters decrease as a result of an inclination to lose electrons decreases because of the increase in nuclear price. Example: Metallic character of 2nd-period elements: Li > Be > B > C >> N > O > F In Group: Metallic persona, when moving from best to bottom increases because the atomic dimension and tendency to lose electrons increases. Example: First workforce part : Li < Na < ok < Rb < Cs

17th group elements: F < Cl < Br < I

iv) Non-metallic character: It is the tendency of an atom to gain electrons. In Period: Along with the era from left to right, the non-metallic personality increases for the reason that tends to achieve electrons increases because of an increase in nucleus charge. Example; Non-metallic character of second-period parts: Li < Be < B < C < N < O < F In Group: On moving from top to bottom in a group, non-metallic character decreases because atomic size increases and tendency to gain electrons decreases. Ex. Non-metallic character of 17th period element: F > Cl > Br > I

v) Chemical Reactivity: In metals: Chemical reactivity of metals increases down the group because the tendency to lose electrons will increase.

Example ; Li < Na < okay < Rb < Cs (1st group) In non-metals: Chemical reactivity of non-metals decreases down the group because tendency to gain electrons decreases. Example: F > Cl > Br > I (17th staff).

vi) Electronegativity: It is the tendency of an element to attract the shared pair of electrons towards it in a covalently bonded molecule. It increases with the rise in nuclear rate or decrease in atomic size. Along the duration electronegativity will increase.

Example ;Li < Be < B < C < N < O < F. Down the group electronegativity decreases. Example ; Li > Na > ok > Rb > Cs F > Cl > Br > I

vii) Nature of Oxides: Metal oxides are basic in nature. Ex. Na2O, MgO, etc.
Non-metal oxides are acidic in nature. Ex. Cl2O7, SO3, P2O5,

Group: The vertical columns in Mendeleev’s, as well as in Modern Periodic Table, are referred to as groups.

Period: The horizontal rows in the Modern Periodic Table and Mendeleev’s Periodic Table is known as classes. There are 18 teams and 7 (seven) classes within the Modern Periodic Table.

Atomic size: The atomic size may be visualized as the distance between the center of the nucleus and the outermost shell of an isolated atom.

The development of atomic measurement (radius) in shifting down a gaggle: Ongoing down in a group of the Periodic Table, the atomic measurement will increase because a brand new shell of electrons is added to the atoms at each step. There is an increase in distance between the outermost shell electrons and the nucleus of the atom.

The pattern of atomic measurement (radius) in transferring from left to right in a length: On transferring from left to right alongside a duration, the scale of atoms decreases because on transferring from left to right, the atomic collection of components increases which means that the collection of protons and electrons in the atoms increases. Due to the massive sure charge on the nucleus, the electrons are pulled in more closely to the nucleus, and the scale of the atom decreases.

  1. Characteristics of triads of J.W. Dobereiner.
  • Elements of a triad show similar chemical properties.
  • These elements of a triad show specific trends in their physical properties.
  • The atomic mass of the middle element was roughly the average of the atomic masses of the other two elements.

For example, The atomic mass of Na is 23 in the triad Li, Na, and K. This atomic mass is the average of the atomic masses of Li and K which have atomic masses 7 and 39 respectively.

2. Dobereiner’s triads: Johann Wolfgang Dobereiner, a German chemist, classified the identified elements in groups of 3 elements on the foundation of similarities of their homes. These teams were known as triads.

i) Characteristics of Triads:

  • Properties of elements in each triad were similar.
  • Atomic mass of the middle element was roughly the average of the atomic masses of the other two elements.

ii) Examples of Triads:

iii) Limitations: Dobreyan’s Cold Identify Only Three Trades. He was not aware of the pre-existing trades of all the conventional elements.

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