CBSE Class 10 Science Chapter 5: Periodic Classification of Elements NCERT Solutions
This chapter delves into the historical development and principles of the periodic classification of elements. It covers early attempts like Döbereiner's Triads and Newland's Law of Octaves, highlighting their limitations. The solutions meticulously explain Mendeleev's Periodic Law, which arranged elements by atomic mass, and the significance of the gaps he left for undiscovered elements. It further elaborates on the Modern Periodic Table, based on increasing atomic number, and its structure of periods and groups. The provided solutions clarify how elements are grouped based on their electronic configurations and chemical properties, aiding students in understanding periodic trends. These solutions are designed to help Class 10 students grasp the fundamental concepts of atomic structure and its relation to elemental properties, crucial for exam preparation.
Quick info
| Board | CBSE |
|---|---|
| Class | Class 10 |
| Subject | Science (Exemplar) |
| Session | 2026 |
| Language | English |
| Type | NCERT Solutions |
| Chapter | 5. Periodic Classification of Elements |
Chapter summary
This chapter focuses on the evolution of the periodic table, from early classification systems to the modern periodic law. It explains the principles behind Mendeleev's Periodic Table and the Modern Periodic Table, emphasizing the arrangement of elements based on atomic mass and atomic number, respectively. The solutions cover the structure of the modern periodic table, including periods and groups, and how electronic configurations determine an element's position and properties. Key concepts like the limitations of earlier laws and the significance of atomic number as the basis for modern classification are detailed.
Learning outcomes
- Understand the historical development of the periodic table.
- Explain Newland's Law of Octaves and its limitations.
- Describe Mendeleev's Periodic Law and its contributions.
- Identify the basis of the Modern Periodic Table (atomic number).
- Recognize the structure of the Modern Periodic Table (periods and groups).
- Relate electronic configuration to an element's position in the periodic table.
Topics covered
Paper topics
- Need for Classification of Elements
- Early Attempts at Classification
- Döbereiner's Triads
- Newland's Law of Octaves
- Limitations of Newland's Law of Octaves
- Mendeleev's Periodic Law
- Mendeleev's Periodic Table
- Gaps in Mendeleev's Table
- Modern Periodic Law
- Modern Periodic Table
- Periods in the Modern Periodic Table
- Groups in the Modern Periodic Table
Important topics
- Mendeleev's Periodic Law and Table
- Modern Periodic Law and Table
- Basis of Modern Classification (Atomic Number)
- Structure of the Modern Periodic Table (Periods and Groups)
- Comparison of Mendeleev's and Modern Periodic Tables
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Questions and Solutions
Question 1
Options: (a) Oxygen (b) Calcium (c) Cobalt (d) Potassium
Newland's Law of Octaves, which stated that every eighth element possessed properties similar to the first when arranged in order of increasing atomic mass, was found to be applicable only up to elements with an atomic mass of approximately 40, which corresponds to Calcium. Beyond Calcium, the properties of the eighth element did not align with the first, indicating a limitation of this law.
Question 2
Options: (a) increasing atomic number (b) decreasing atomic number (c) increasing atomic masses (d) decreasing atomic masses
Mendeleev's Periodic Law proposed that the physical and chemical properties of elements are a periodic function of their atomic masses. Consequently, he arranged the elements in his periodic table in the order of their increasing atomic masses.
Question 3
Options: (a) Germanium (b) Chlorine (c) Oxygen (d) Silicon
Mendeleev ingeniously left gaps in his periodic table for elements that were yet to be discovered. He named these hypothetical elements 'Eka-Boron', 'Eka-Aluminum', and 'Eka-Silicon'. Later, when Germanium was discovered, its properties closely matched those predicted for Eka-Silicon, confirming the validity of Mendeleev's predictions and its placement in the table.
Question 4
Statements:
(i) The elements in the Modern Periodic Table are arranged on the basis of their decreasing atomic number.
(ii) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic masses.
(iii) Isotopes are placed in adjoining groups in the Periodic Table.
(iv) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic number.
Options:
(a) (i) only
(b) (i), (ii) and (iii)
(c) (i), (ii) and (iv)
(d) (iv) only
Let's analyze each statement:
(i) This statement is incorrect because the Modern Periodic Table arranges elements based on increasing atomic number, not decreasing atomic number.
(ii) This statement is incorrect. The Modern Periodic Table is based on atomic number, not atomic mass. Arranging by atomic mass was the basis of Mendeleev's table.
(iii) This statement is incorrect. Isotopes of an element have the same atomic number and thus occupy the same position in the Modern Periodic Table; they are not placed in adjoining groups.
(iv) This statement is correct. The fundamental principle of the Modern Periodic Table is the arrangement of elements in order of their increasing atomic number.
Therefore, statements (i), (ii), and (iii) are incorrect.
Question 5
Options: (a) It has 18 horizontal rows known as Periods. (b) It has 7 vertical columns known as Periods. (c) It has 18 vertical columns known as Groups. (d) It has 7 horizontal rows known as Groups.
The Modern Periodic Table is structured with 7 horizontal rows, which are called Periods, and 18 vertical columns, which are called Groups. Option (a) incorrectly identifies rows as periods and the number as 18. Option (b) incorrectly identifies columns as periods. Option (d) incorrectly identifies rows as groups.
Question 6
Options: (a) A, B, C (b) B, C, D (c) A, D, E (d) B, D, E
The period number of an element is determined by the number of the outermost electron shell. Let's determine the period for each element based on its atomic number: Element A (Atomic Number = 2): This is Helium (He). Its electronic configuration is 1s². It belongs to Period 1. Element B (Atomic Number = 3): This is Lithium (Li). Its electronic configuration is 1s²2s¹. It belongs to Period 2. Element C (Atomic Number = 7): This is Nitrogen (N). Its electronic configuration is 1s²2s²2p³. It belongs to Period 2. Element D (Atomic Number = 10): This is Neon (Ne). Its electronic configuration is 1s²2s²2p⁶. It belongs to Period 2. Element E (Atomic Number = 30): This is Zinc (Zn). Its electronic configuration is 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰. It belongs to Period 4. Elements B, C, and D all have their outermost electrons in the second shell (n=2), hence they belong to the same period, which is Period 2.
Common mistakes
- Confusing atomic mass with atomic number as the basis for the Modern Periodic Table.
- Incorrectly applying Newland's Law of Octaves beyond Calcium.
- Misunderstanding the arrangement of isotopes in the periodic table.
- Confusing the terms 'period' and 'group'.
Revision tips
- Focus on the key differences between Mendeleev's and the Modern Periodic Table.
- Memorize the basis of classification in each periodic system (atomic mass vs. atomic number).
- Understand why isotopes are placed in the same group in the Modern Periodic Table.
- Practice identifying elements belonging to the same period or group based on their atomic numbers.
Practice MCQs
Q1. According to Newland's Law of Octaves, which element's properties were found to be similar to the first element in a series?
Explanation: Newland's Law of Octaves stated that every eighth element, when arranged in order of increasing atomic mass, possessed properties similar to the first element, analogous to the eighth note in a musical scale.
Q2. Mendeleev's Periodic Law was based on the arrangement of elements in order of their:
Explanation: Mendeleev arranged elements in his periodic table based on their increasing atomic masses, which helped in establishing a relationship between atomic mass and the properties of elements.
Q3. Which of the following elements was predicted by Mendeleev and later discovered, fitting into his periodic table?
Explanation: Mendeleev left gaps for undiscovered elements and named them Eka-Silicon, Eka-Aluminum, and Eka-Boron. Germanium was later discovered and found to correspond to Eka-Silicon.
Q4. Which statement about the Modern Periodic Table is incorrect?
Explanation: The Modern Periodic Table arranges elements based on increasing atomic number. Isotopes have the same atomic number and thus occupy the same position in the periodic table.
Q5. In the Modern Periodic Table, vertical columns are known as:
Explanation: The vertical columns in the Modern Periodic Table are called Groups, and they contain elements with similar valence electron configurations, leading to similar chemical properties.
Q6. Elements with atomic numbers 2, 10, and 30 belong to which category based on their electronic configuration and position?
Explanation: Atomic number 2 is Helium (He), 10 is Neon (Ne), and 30 is Zinc (Zn). Helium and Neon are noble gases (Group 18). While Zinc is in Period 4, it doesn't share the same period or group with He and Ne.
Frequently asked questions
What is the basis of Mendeleev's Periodic Table?
Mendeleev's Periodic Table is based on the arrangement of elements in order of their increasing atomic masses. He observed that the properties of elements repeated at regular intervals when arranged in this manner.
What is the basis of the Modern Periodic Table?
The Modern Periodic Table is based on the Modern Periodic Law, which states that the physical and chemical properties of elements are periodic functions of their atomic numbers. Elements are arranged in order of increasing atomic number.
What are the limitations of Newland's Law of Octaves?
Newland's Law of Octaves was applicable only up to Calcium (the 20th element). Also, it assumed that only 56 elements existed in nature and that no new elements would be discovered. It did not leave any place for undiscovered elements, and the properties of some elements did not fit the pattern.
How are elements arranged in the Modern Periodic Table?
Elements are arranged in the Modern Periodic Table in order of increasing atomic number. Elements with similar electronic configurations and chemical properties are placed in the same vertical column (group).
What is the difference between a period and a group in the Modern Periodic Table?
Periods are the horizontal rows in the Modern Periodic Table, representing the principal energy levels (shells) being filled. Groups are the vertical columns, representing elements with the same number of valence electrons and similar chemical properties.
Why are isotopes placed in the same position in the Modern Periodic Table?
Isotopes of an element have the same atomic number because they have the same number of protons. Since the Modern Periodic Table is arranged based on atomic number, all isotopes of an element occupy the same position.
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