NCERT Solutions for Class 10 Science Chapter 5 Periodic Classification of Elements

NCERT Solutions for Class 10 Science Chapter 5 – CBSE Access Free PDF

*According to the latest update on the CBSE Syllabus 2023-24, this chapter has been removed.

NCERT Solutions for Class 10 Science Chapter 5 – Periodic Classification of Elements at BYJU’S provides detailed solutions to all the questions as per CBSE guidelines. The NCERT solutions are in sync with the questions provided in the NCERT textbook and have been solved by subject-matter experts in accordance with the understanding level of Class 10 students. The NCERT textbook is carefully designed so as to allow students to build complete knowledge of the subject.

The NCERT Solutions furthermore ease the task of students for last-minute studies. The solutions provided are accurate and simple. The main aim of providing students with NCERT Solutions for Class 10 Science is to be beneficial to students, saving time that they spend browsing through different websites for solutions. It is an ultimate one-stop-shop for all their learning requirements and serves as an effective reference tool.

NCERT Solutions for Class 10 Science Chapter 5 – Summary:

• Elements are classified on the basis of similarities in their properties.
• Döbereiner grouped the elements into triads and Newlands gave the Law of Octaves.
• Mendeléev arranged the elements in increasing order of their atomic masses and according to their chemical properties.
• Mendeléev even predicted the existence of some yet-to-be-discovered elements on the basis of gaps in his Periodic Table.
• Anomalies in the arrangement of elements based on increasing atomic mass could be removed when the elements were arranged in order of increasing atomic number, a fundamental property of the element discovered by Moseley.
• Elements in the Modern Periodic Table are arranged in 18 vertical columns called groups and 7 horizontal rows called periods.
• Elements thus arranged show periodicity of properties including atomic size, valency or combining capacity and metallic and non-metallic character.

NCERT Solutions for Class 10 Science Chapter 5 Periodic Classification of Elements

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Access Answers to NCERT Class 10 Science Chapter 5 – Periodic Classification Of Elements ( All In text and Exercise Questions Solved)

Questions Page number 81

1. Did Döbereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.

Solution:

Döbereiner’s triads did exist in the columns of Newlands’ Octaves; For example, the elements

Lithium (Li), Potassium (K) and Sodium (Na) constitute a Dobereiner’s Triad but are also found in the second column of Newland’s Octaves.

2. What were the limitations of Döbereiner’s classification?

Solution:

(i) They were not applicable for very low mass or very high mass elements.

(ii) All the elements couldn’t fit into Dobereiner’s triads.

(iii) As the methods to calculate atomic mass improved, Dobereiner’s triads’ validity began to decrease. For example, in the triad of F, Cl and Br, the arithmetic mean of atomic masses of F and Br is not equal to the atomic mass of CI.

3. What were the limitations of Newlands’ Law of Octaves?

Solution:

Limitations of Newlands’ Law of Octaves are as follows:

• Newlands’ Law of Octaves is applicable only to elements up to Calcium
• Newland assumed there were 56 elements in nature and no more elements would be discovered in the future.
• To fit elements into the table, Newland put two elements into one slot. Newland introduced unlike elements with different properties into one column.
• Iron (Fe) was placed away from elements that resemble in properties. Ex: Nickel and cobalt

Questions Page number 85

1. Use Mendeleev’s Periodic Table to predict the formulae for the oxides of the following elements: K, C, AI, Si, Ba.

Solution:

K- K₂O

C-C₂O₄ or CO₂

Al- Al₂O₃

Si-Si₂O₄ or SiO₂

Ba₂O₂ or BaO

Oxygen is a member of group VI A in Mendeleev’s periodic table. Its valency is 2. Similarly, the valencies of all the elements listed can be predicted from their respective groups. This will help in writing the formulae of their oxides.

(i) Potassium (K) is a member of group IA. Its valency is 1. Therefore, its formula is K₂O.

(ii) Carbon (C) is a member of group IV A. Its valency is 4. Therefore, the formula is C₂O₄ or CO₂.

(iii) Aluminium (Al) belongs to groups III A and its valency is 3. The formula of its oxide is Al₂O₃.

(iv) Silicon (Si) is present in group IV A after carbon. Its valency is also 4. The formula of oxide is Si₂O₄ or SiO₂.

(v) Barium (Ba) belongs to group II A and the valency of the element is 2. The formula of the oxide of the element is Ba₂O₂ or BaO.

2. Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (Any two)

Solution:

Germanium and Scandium are the elements that are left by Mendeleev in his Periodic Table since its discovery.

3. What were the criteria used by Mendeleev in creating his Periodic Table?

Solution:

Mendeleev concentrated on various compounds formed by the elements with Hydrogen and Oxygen. Among physical properties, he observed the relationship between the atomic masses of various elements while creating his periodic table.

4. Why do you think the noble gases are placed in a separate group?

Solution:

Noble gases are placed in a separate group because of their inert nature and low concentration in our atmosphere. They are kept in a separate group called the Zero group so that they don’t disturb the existing order.

Questions Page number 90

1. How could the Modern Periodic Table remove various anomalies of Mendeleev’s Periodic Table?

Solution:

(a) In the Modern Periodic table, elements are arranged in the increasing order of their atomic number. This removes the anomaly regarding certain pairs of elements in Mendeleev’s periodic table.

(b) The Atomic number of cobalt is 27, and that of nickel is 28. Hence, cobalt will come before nickel even though its atomic mass is greater.

c) All isotopes of the same elements have different atomic masses but the same atomic number; therefore, they are placed in the same position in the modern periodic table.

2. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?

Solution:

Calcium and Beryllium are similar to Magnesium because all three elements belong to the same group and have 2 valence electrons in their outer shell.

3. Name

(a) Three elements that have a single electron in their outermost shells.

(b) Two elements that have two electrons in their outermost shells.

(c) Three elements with filled outermost shells

Solution:

1. Lithium (Li), Sodium (Na) and potassium (k) have a single electron in their outermost shells.
2. Magnesium (Mg) and Calcium (Ca) have two electrons in their outermost shells
3. Neon (Ne), Argon (Ar and Xenon (Xe) filled outermost shells

4. a) Lithium, sodium, and potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?

(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?

Solution:

They’ve one valence electron in their outermost shells, and as a result of this, they are very unstable. So, they readily react with water to liberate hydrogen. They are also called alkali metals.

Their outermost shells are full, leading to high stability. They react only in extreme circumstances and hence are called noble gases.

5. In the Modern Periodic Table, which are the metals among the first ten elements?

Solution:

Lithium and Beryllium are the metals among the first ten elements in the Modern Periodic Table.

6. By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristic? Ga Ge As Se Be

Solution:

Among the elements listed in the question. Be and Ga are expected to be the most metallic. Out of Be and Ga, Ga is bigger in size and hence has a greater tendency to lose electrons than Be. Therefore, Ga is more metallic than Be.

Exercise questions Page number 91-92

1. Which of the following statements is not a correct statement about the trends when going from left to right across the periods of Periodic Table.

(a) The elements become less metallic in nature.

(b) The number of valence electrons increases.

(c) The atoms lose their electrons more easily.

(d) The oxides become more acidic

Solution:

The correct answer is c . The atoms lose their electrons more easily.

The atoms lose their electrons more easily is a wrong statement because as we move from left to right across the periods of the periodic table, the non-metallic character increases.

Therefore, the tendency to lose an electron decreases.

2. Element X forms a chloride with the formula XCl₂, which is a solid with a high melting point. X would most likely be in the same group of the Periodic Table as (a) Na (b) Mg (c) AI (d) Si

Solution:

The answer is Magnesium because Mg has the valency 2, which is the same as the group (a) Na (b) Mg (c) AI (d) Si

Also, Mg, when combined with chloride, forms MgCl₂.

3. Which element has?

(a) Two shells, both of which are completely filled with electrons?

(b) The electronic configuration 2, 8, 2?

(c) A total of three shells, with four electrons in its valence shell?

(d) A total of two shells, with three electrons in its valence shell?

(e) twice as many electrons in its second shell as in its first shell?

Solution:

a) Neon has two shells which are completely filled.

b) Magnesium has electronic configuration 2, 8, 2

c) Silicon has a total of three shells, with four electrons in its valence shell

d) Boron has a total of two shells, with three electrons in its valence shell

e) Carbon has twice as many electrons in its second shell as in its first shell

4. (a) What property do all elements in the same column of the Periodic Table as boron have in common?

(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?

Solution:

(a) All the elements which lie in me same column as that of boron belong to group 13. Therefore, they have three electrons in their respective valence shells. Except, boron which is a non-metal, all other elements (i.e., aluminum, gallium, indium and thallium) in this group are metals.

(b) All elements in the same column of the Periodic Table as fluorine have in common three electrons in their valence shell and they all belong to group thirteen.

5. An atom has electronic configuration 2, 8, 7.

(a) What is the atomic number of this element?

(b) To which of the following elements would it be chemically similar? (Atomic numbers are given in parentheses.) N(7), F(9), P(15), Ar(18)

Solution:

(a)The element with electronic configuration (2+8+7) 17 is chlorine.

The no. of atomic number = no. of electrons

Therefore, the atomic number is 17.

(b) An atom with electronic configuration 2, 8, 7 would be chemically similar to F (9)

6. The position of three elements A, B and C in the Periodic Table are shown below–

Group 16          Group 17

–                                –

–                                A

–                                –

B                               C

(a) State whether A is a metal or non-metal.

(b) State whether C is more reactive or less reactive than A.

(c) Will C be larger or smaller in size than B?

(d) Which type of ion, cation or anion, will be formed by element A?

Solution:

1. Element A is a non-metal
2. Element C is less reactive than Element A
3. C is smaller in size than B
4. A will form anion

7. Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?

Solution:

The atomic number of Nitrogen is 7 hence Electronic configuration of Nitrogen is 1s² 2s² 2p³

The atomic number of Nitrogen is 15 hence Electronic configuration of Phosphorous is 1s² 2s² 2p⁶ 3s² 3p³

On moving down a group in the periodic table, the number of shells increases. Due to this, valence electrons move away from the electrons and the effective nuclear charge decreases. This causes a decrease in the tendency to attract electrons and hence electro negativity decreases. Because of all these reasons Nitrogen is more electronegative than phosphorus.

8. How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?

Solution:

The number of valence electrons decides an atom’s position in the periodic table, while the electronic configuration decides the number of valence electrons.

9. In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38. Which of these have physical and chemical properties resembling calcium?

Solution:

Calcium has an atomic number of 20 and thus has an electronic configuration of 2, 8, 8, 2. Thus, calcium has 2 valence electrons. The electronic configuration of the element having atomic number 12 is 2, 8.2. Thus, this element with 2 valence electrons resembles calcium the most.

10. Compare and contrast the arrangement of elements in Mendeleev’s Periodic Table and the Modern Periodic Table.

Solution:

NCERT Solutions for Class 10 Science Chapter 5- Periodic Classification Of Elements

NCERT Class 10 Science Chapter 5- Periodic Classification of Elements is categorized under Unit Chemical Substances – Nature and behaviour. This unit, on the whole, comprises 25 marks in the board exam, with the most marks compared to any other chapter in the syllabus. Hence, all chapters in Unit Chemical Substances need to be studied thoroughly. Periodic classification of elements chapter alone holds 5 marks in the CBSE exam as expected and from a careful analysis of previous question papers.

List of subtopics covered in Chapter 5 – Periodic Classification Of Elements:

5.1 Making Order Out of Chaos – Early Attempts At the Classification of Elements

We have been learning how various things or living beings can be classified on the basis of their properties. Even in other situations, we come across instances of organisations based on some properties. The topic discusses concepts of Dobereiner’s Triads and Newlands’ Law of Octaves. Both concepts are explained with suitable examples.

5.2 Making Order Out of Chaos – Mendeleev’s Periodic Table

The topic explains Mendeleev’s Periodic table, achievements of Mendeleev’s Periodic Table and Limitations of Mendeleev’s Classification. The concepts are presented along with the periodic table and Dmitri Ivanovich Mendeleev’s creation of the periodic table.

5.3 Making Order Out of Chaos – The Modern Periodic Table

The Modern Periodic Table states that the properties of elements are a periodic function of their atomic number. The topic further discusses the Position of Elements in the Modern Periodic Table, trends in the Modern Periodic table, such as valency, Atomic Size, Metallic and Non – metallic Properties.

List of Exercise with questions

Number – 5.1 – Making order out of chaos 3 Questions (2 long, 1 short)

-Early attempts at the classification of elements

Number – 5.2 – Making order out of chaos

– Mendeleev’s Periodic Table 4 Question (1 long, 3 short)

Number – 5.3 – Making order out of chaos

-The Modern Periodic table 6 Question (1 long, 5 short)

Exercise Solutions – 10 Question (2 long, 8 short)

NCERT Solutions for Class 10 Science Chapter 5 – Periodic Classification of Elements

Periodic Classification of elements gives a brief idea about how elements are classified based on the similarities in the properties shared by different elements. It briefly discusses how Dobereiner classified various elements into triads and how Newland proposed the Law of Octaves. The chapter also briefly discusses the arrangement of elements in increasing order of their atomic numbers and chemical properties as suggested by Mendeleev, as he even predicted the existence and presence of some more elements that were to be yet discovered, which he arrived at due to gaps in the Periodic table.

The chapter also talks about the limitations of Mendeleev’s classification and hence the modern periodic table. It gives an idea of the positioning of elements in the modern periodic elements and also the vertical and horizontal arrangement known as groups and periods, respectively.

Key Features of NCERT Solutions for Class 10 Science Chapter 5 – Periodic Classification Of Elements

• NCERT Class 10 Solutions are answered considering chapter-wise marks distribution and question type aligning with the CBSE blueprint of Science
• Solutions have been elaborated, enabling students to understand better
• Numerical have been solved, giving a step-by-step explanation
• Tabular columns have been used wherever necessary, which enables students to learn at a faster pace
• The language used in the chapter is simplified and logical