Class 10 Science Chapter 5 Periodic Classification of Elements

Here in class 10 science chapter 5 periodic classification of elements, we are going to study the different periodic tables, their history, and many more interesting facts. Make sure to read the whole article so that you can understand all the concepts clearly.

First, we will learn about the history and eventually move on towards the modern time-periodic table. However, as we have learned in class 9th, matter around us is in the form of elements, compounds, and mixtures. So, different scientists gave their studies while classifying the different elements in the periodic table. Such as Dobereiner, Newlands, and Mendeleev.

Class 10 Science Chapter 5 Periodic Classification of Elements

In this section of Class 10 Science Chapter 5 Periodic Classification of Elements, we are going to learn about the history of the periodic classification of elements.

# History of the periodic table

The date goes back to the 1800s when there were only 30 elements are present, but now today we have 118 elements present. Scientists tend to find some pattern in all the elements so, that they can arrange all the elements in the periodic table.

However, the 1st attempt to classify the atoms is done by metals and non-metals but after they get information about their properties they started classifying them using a completely different approach. So, let’s see which scientists use which approach and what are the results.

# Dobereiner’s Triads

Here we will learn about the approach of a scientist named Dobereiner. How he approaches it and what are the results.

What are Dobereiner’s Triads?

In 1817, he tried to arrange all the elements which share similar properties into a  group. So, he makes the group using 3 elements which are further known as triads. His triad is based on the atomic mass of the element.

So, further, he said that if we group all 3 elements according to the increasing atomic mass of the elements, then the atomic mass of the middle element is equal to the average of the other 2.

Example: Lithium (Li), Sodium (Na), Potassium (K) ⇒ Li (6.9), Na (23), K (39)

So: (39+6.9)/2 = 45.9/2 = 22.95 ~ 23 (Na)

Which elements are in Dobereiner’s Triads?

See the table below.

Elements of Dobereiner’s Triads
Li (6.9) Ca (40) Cl (35.4)
Na (23) Sr (87.6) Br (79.9)
K (39) Ba (137.3) I (126.9)

# Limitations of Dobereiner’s Triads

He could only identify 3 elements for its triad from all of the present elements at that time. So, when the number of the elements increased this classification was not useful as it was not able to fit in all of the elements in the triad.

Class 10 Science Chapter 5 Periodic Classification of Elements

Let’s now take a look at the Newlands law of octaves.

What is Newland’s Law of Octaves?

In 1866, he also tries to classify by using atomic mass and also group or classify the elements by increasing atomic mass.

How many elements were there in 1866?

Total elements present in 1866 were “56”.

So, in his classification, he found that every 8th element in the group have a similar property as of 1st element. Such as Hydrogen (H) ~ Florine (F).

He named his law octave because it is named after the musical notes i.e “sa, re, ga, ma, pa, dha, ni, sa”. So, the 8th note has the same sound as of 1st note. Now let’s talk about the limitation of this classification down.

# Limitations of Newland’s Law of Octaves

  1. It is only applicable up to Calcium (Ca)
  2. He only assumed that there are only 56 elements and there are new elements that repel the Newland’s Law of Octaves.
  3. To fit all the elements in the table, he put 2-2 elements in the same slot. Whether their property is similar or not.

Now, down in the article let’s talk about another classification of elements i.e Mendeleev’s Periodic Table.

Class 10 Science Chapter 5 Periodic Classification of Elements

In this section of Class 10 Science Chapter 5 Periodic Classification of Elements, we are going to learn about Mendeleev’s Periodic Table.

This is the most popular periodic table, which you will study in your future classes as well. So let’s see what approach did he choose while making his table.

He did the arrangement of the elements according to their atomic mass and also on the similarity of their chemical property. There were only 63 elements present at that time.

He tried to make the relationship of the atomic mass of the elements between their physical and chemical properties. For the chemical properties, he concentrated on the element which has hydrogen and oxygen because they are most reactive and react with most of the elements.

He created the formula of the elements for Hybrid and Oxide, depending on these, he put this into different positions and then classified them. He sorts the element according to similar chemical properties. He observed that all of the elements are automatically sorted out according to the increase in atomic mass.

He also observed that after a specific time those elements which have similar properties are occurring again and again or we can say that they are repeating.

What is a Periodic Law?

It states that all the elements which show similar properties occur after a regular time period when sorting them according to their increase in their atomic mass.

In the Periodic Table, the verticle columns are called groups, and horizontal columns are called periods. Now let’s learn about the Achievements of this classification.

Class 10 Science Chapter 5 Periodic Classification of Elements

In this section of Class 10 Science Chapter 5 Periodic Classification of Elements, we are going to learn about the achievements of Mendeleev’s Periodic Table.

# Achievements of Mendeleev’s Periodic Table

He creates his periodic table according to the increment on the atomic mass of an element, but sometimes to match the chemical property of the element he puts the higher atomic mass element before the element which has a lower atomic mass.

For Example Cobalt (58.9) comes before Nickel (58.7)

He also leaves some gaps in the table and predicts that in the future there are some elements that could be discovered which can fill these gaps.

He named them by using the prefix from the Sanskrit numeral i.e “Eka” which means one (1). See the example below:

For Example Eka-Boron, Eka-Aluminium, and Eka-Silicon. However, later these elements are replaced by the other elements with similar properties named Scandium, Gallium, and Germanium respectively. See the table below.

Properties Eka-Aluminium Scandium
Atomic Mass 68 69.7
Oxide formula E2O3 Ga2O3
Chloride formula ECl3 GaCl3

Why were Helium, Neon, and Argon discovered late?

This is because they are very inert and only available in extremely low concentrations. However, when they are being discovered all these gasses could be put in the group without disturbing the order.

# Limitation of Mendeleev’s Periodic Table

Here are some limitations listed regarding Mendeleev’s Periodic Table.

  1. The position of Hydrogen is not fixed because hydrogen has similar properties to both the alkali and halogen families. It has the same electronic configuration as alkali and Halogen. Also, have similar chemical properties as alkali and Halogen. It is because Hydrogen is diatomic (H2) exactly like halogens and makes the compound in the same way as it makes with the alkali.
  2. Isotopes are discovered after the periodic table is released. So, you have to put hydrogen according to the atomic mass due to the Periodic Law.
  3. Elements are not in the perfect order according to the atomic mass. So, you can’t know that how many elements are predicted between the 2 elements.

What are Isotopes?

They are like Hydrogen. They have the same atomic number but different atomic masses. See the example below.
Example: H_1^1,\ H_1^2,\ H_1^3

Class 10 Science Chapter 5 Periodic Classification of Elements

In this section of Class 10 Science Chapter 5 Periodic Classification of Elements, we are going to learn about the Modern Periodic Table.

As you can see in your science book there are different colors are given in the periodic table, did you wonder why? So let us tell you that.

These colors represent different types of elements i.e Metals are represented as green, Non-metals are represented as yellow, and Metalloids are represented as pink.

Also in the table, you can see that there is a difference between the number of some elements such as “La (57) & Hr (72)”. So, this is because those between elements are put outside the table, so that study could be done easily.

You also wonder why there is a huge gap in the table between the elements, so you will get to learn more about the modern periodic table in Class 11. Check out our website as we cover all of the classes and their all chapters.

# Posiotion of Elements in the Modern Periodic Table

All the positions of elements in the Periodic Table are according to their chemical reactivity because valence electrons determined the number of bonds formed by an element.

It has 18 verticle columns also called “group” and 7 horizontal columns also called “period”. So, all the elements present in a group have the same valance electron in their outermost shell. For example F (7) and Cl (17).

Also, as you can see that in the table the number of valance electrons of those elements which are in the “period” is increasing by 1 as their atom is increasing by 1. For example Li (3) and Be (4).

How many electrons are there in each period?

You can calculate the electrons in a period based on the number of electrons in the shells. So, to calculate this you just need to use a formula i.e. 2n².

There are different names given to the different groups such as “K, L, M, N, O, P, and Q” are given named “1, 2, 3, 4, 5, 6, and 7”.

So, by using the formula:

  • K-shell = 2 x (1)², which means 1st period has 2 elements.
  • L-shell = 2 x (2)², which means 2nd period has 8 elements.

Similarly, 3, 4, 5, 6, and 7 has “8, 18, 18, 32, and 32” respectively. Although, you are wondering if the calculation of 3, 4, 5, 6, and 7 periods are not exact to the formula of 2n². So, the reason behind this is what you will learn in the higher classes.

Class 10 Science Chapter 5 Periodic Classification of Elements

In this section of Class 10 Science Chapter 5 Periodic Classification of Elements, we are going to learn about the trends in the modern periodic table.

# Trends in Modern Periodic Table

It means that if you go from left to right in the periodic table the atomic size decreases or increases and if you go from up to down the atomic size increases or decreases.

So, if you go from up to down in the table the atomic radius and number increase. Also, if you go from right to left the atomic size and number increase.

1. Valency

As we already discussed that it is the number of valence electrons present in the outermost shell. So, if we go according to the group the valence of electrons is remains the same. However, if we go according to the period the valence of the electron increase.

For example:

  • Hydrogrn (H) = 1
  • Litium (Li) = 2, 1
  • Sodium (Na) = 2, 8, 1

All these elements have 1 electron in their outermost shell.

2. Atomic Size

It is also known as the radius of the atom. It may be identified by the distance between the center of an atom to its outermost shell. So, if we move from up to down the atomic size and shell number increases.

If you go left to right, then there is no increment on the shell but electron and protons are increases. Therefore, the atomic number increases but atomic size decreases. As the more electrons are in the shell the stronger bond it makes with its nuclear.

3. Metallic and Non-Metallic properties

All of the metals are found on the left side of the table and all of the non-metals are found on the right side of the table. Also, all the metalloids form a zig-zag line on the right side of the table.

All metals tend to lose electrons. So, from up to down the tendency to lose electrons increases, and it’s easy to lose the outermost electron due to the increasing distance of electrons from the proton.

If we move across the period (Left to right), then the tendency to lose electrons decreases, and the bond between outermost electron and proton becomes strong.

If atomic charge increases then the force of attraction also increases, so it’s difficult to lose the outermost electron. However, Non-Metallic tends to gain electrons.

So, if you go from left to right, then the tendency of gaining electrons increases. Also, if you go from up to down, then the tendency of gaining electrons decreases.

Class 10 Science Chapter 5 Periodic Classification of Elements

In this section of Class 10 Science Chapter 5 Periodic Classification of Elements, we are going to see the blueprint and more important things related to this chapter.

To see Class 10 Science Chapter 5 Periodic Classification of Elements blueprint down in the table.

Class 10 Science Chapter 5 Periodic Classification of Elements
3 Marker 1 questions
4 Marker 1 question
Total questions 2
Total marks 7
Class 10 Science Chapter 5 Periodic Classification of Elements Blueprint 2021-22

The total worth of Class 10 Science Chapter 5 Periodic Classification of Elements in terms of the board exam. According to the table, this chapter contains 3 marks for 1 question and 4 marks for 1 question. Please note that this marking scheme may vary in board exams.

So, this is all the information you want to know about the Class 10 Chapter 5 Periodic Classification of Elements.

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Updated: January 10, 2022 — 5:24 am

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