Lakhmir Singh Solutions for Class 10 Chemistry Chapter 5: This chapter explains how elements are classified based on their properties, covering early classification attempts like Dobereiner’s Triads, Newlands’ Law of Octaves, and Mendeleev’s Periodic Table. It then focuses on the modern periodic table, which arranges elements based on atomic number.
Key concepts include groups, periods, trends in atomic size, valency, ionization energy, electronegativity, and metallic and non-metallic properties. The solutions help students understand periodic trends with solved examples, reasoning-based questions, and numerical problems, making it easier to grasp classification principles and their significance in Chemistry.
Lakhmir Singh Solutions for Class 10 Chemistry Chapter 5 Overview
This chapter is crucial for understanding the systematic arrangement of elements in the periodic table. It explains classification methods like Dobereiner’s Triads, Newlands’ Law of Octaves, Mendeleev’s Periodic Table, and the Modern Periodic Table.
These solutions help students grasp periodic trends in atomic size, valency, ionization energy, and electronegativity, which are essential for predicting element behavior. By solving conceptual and numerical problems, students develop analytical skills and a strong foundation for advanced chemistry. Understanding periodic classification is vital for real-world applications in industries, research, and material science, making it a fundamental topic in chemistry education.
Lakhmir Singh Solutions for Class 10 Chemistry Chapter 5 PDF
Understanding the periodic classification of elements is essential for mastering chemistry concepts. This chapter explains the evolution of the periodic table, periodic trends, and their significance. To help students, we have provided a PDF containing detailed solutions to all textbook questions. These solutions will enhance conceptual clarity and problem-solving skills, making exam preparation easier. Download the PDF below for comprehensive guidance.
Lakhmir Singh Solutions for Class 10 Chemistry Chapter 5 PDF
Lakhmir Singh Solutions for Class 10 Chemistry Chapter 5 Periodic Classification of Elements
1. (a) On what basis did Mendeleev arrange the element in his periodic table?
(b) On what basis are they arranged now?
Solution:
(a) On the basis of atomic masses, Mendeleev arranged the elements in his periodic table.
(b) Now arranged on the basis of atomic numbers.
2. State whether the following statements are true or false:
(a) Newlands divided the elements into horizontal rows of eight elements each.
(b) According to Mendeleev’s periodic law, the properties of elements are a periodic function of their atomic numbers.
(c) The elements in a group have consecutive atomic numbers.
Solutions:
(a)False. Newlands divided the elements into horizontal rows of seven elements each.
(b) False. According to Mendeleev’s periodic law, the properties of elements are a periodic function of their atomic masses
(c) False. The elements in a period have consecutive atomic numbers.
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3. Name the Russian chemist who said that the properties of elements are a periodic function of their atomic masses.
Solution:
Mendeleev said that the properties of elements are a periodic function of their atomic masses.
4. Rewrite the following statements after correction, if necessary:
(a) Groups have elements with consecutive atomic numbers.
(b) Periods are the horizontal rows of elements.
(c) Isotopes are the elements of the same group.
Solution:
(a) Periods have elements with consecutive atomic numbers.
(b) Correct statement
(c) Correct statement
5. Name the scientists who gave the following laws in the early classification of elements:
(a) Law of octaves (b) Law of triads
Solution:
(a) Newlands put forth the law of octaves.
(b) Dobereiner put forth the law of triads.
6.A, B and C are the elements of Dobereiner’s triad. If the atomic mass of A is 7 and that of C is 39, what should be the atomic mass of B?
Solution:
Mass of A is 7
Mass of C is 39
Mass of B = 7+39/2 = 23
7. X and Y are the two elements having similar properties which obey Newlands’ law of octaves. How many elements are there in-between X and Y?
Solution:
Six elements will be there in between X and Y. Since X and Y are the two elements having similar properties and obey Newlands law of octaves.
8. What was Mendeleev’s basis for the classification of elements?
Solution:
Mendeleev’s basis for the classification of elements was the atomic mass of elements.
9. In the classification of the then-known elements, Mendeleev was guided by two factors. What are those two factors?
Solution:
1. Increasing atomic masses
2. Grouping together of elements having the same properties.
10. Name two elements whose properties were predicted on the basis of their positions in Mendeleev’s periodic table.
Solution:
Gallium and Scandium are the two elements whose properties are predicted on the basis of their positions in Mendeleev’s periodic table.
11.The three elements predicted by Mendeleev from the gaps in his periodic table were known as eka-boron, eka – aluminium and eka-silicon. What names were given to these elements when they were discovered later on?
Solution:
Scandium, Gallium, and Germanium are the three elements predicted by Mendeleev from the gaps in his periodic table and were known as eka-boron, eka – aluminium and eka-silicon.
12. Name two elements whose properties were predicted on the basis of their positions in Mendeleev’s periodic table.
Solution:
Eka- Aluminium (gallium) and Eka-Silicon (germanium) are the two elements whose properties were predicted on the basis of their positions.
13. State one example of Dobereiner’s triad, showing in it that the atomic mass of the middle element is halfway between those of the other two.
Solution:
Lithium, sodium and potassium are said to be triads in Mendeleev’s periodic table. Lithium is the first element in the triad and sodium, being middle, has an atomic mass of 23 and the third element is potassium.
Atomic mass of sodium = At. Mass of Li + At. Mass of K / 2
= 7+39/2
=23
14. Which group of elements could be placed in Mendeleev’s periodic table later on without disturbing the original order? Give reason.
Solution:
Noble gases which are chemically reactive and more stable could be placed in the periodic table in the form of a separate group.
15. Fill in the following blanks with suitable words:
(a) The basis for the modern periodic table is ______.
(b) The horizontal rows in a periodic table are called ______.
(c) Group 1 elements are called ______.
(d) Group 17 elements are known as ______.
(e) Group 18 elements are called ______.
(f) According to Newlands’ classification of elements, the properties of sulphur are similar to those of oxygen because sulphur is the ______ element starting from oxygen.
Solution:
(a) Atomic number.
(b) Periods.
(c) Alkali metals.
(d) Halogens.
(e) Noble Gases.
(f) Eighth.
Short Answer Type Questions
16.(a) What is meant by (i) a group, and (it) a period, in a periodic table?
(b) How many periods and groups are there in the long form of periodic table?
(c) Give two examples each of (i) group 1 elements (ii) group 17 elements (iii) group 18 elements.
Solution:
(a) Groups are the vertical columns in the periodic table
(i) A period is the horizontal rows of elements in the periodic table.
(b) There are seven periods and eighteen groups in the long form of [periodic table.
(c) (i) Group 1: Lithium and Sodium.
(ii) Group 17: Fluorine and Chlorine.
(iii) Group 18: Neon and Argon.
17. (a) In the modem periodic table, which are the metals among the first ten elements?
(b) What is the significance of the atomic number in the modern classification of elements? Explain with the help of an example.
Solution:
(a) In the modern periodic table, lithium and beryllium are the only metals among the first ten elements.
(b) The atomic number is important in the periodic table because elements are arranged based on their electronic configuration. Elements in the same group have similar chemical properties.
For example, lithium has an atomic number of 3, with an electronic configuration of 2,1. Since it has one valence electron, it is placed in Group 1. Similarly, sodium (atomic number 11) has an electronic configuration of 2,8,1 and also belongs to Group 1 because it has one valence electron.
18. (a) How were the positions of isotopes of an element decided in the modern periodic table?
(b) How were the positions of cobalt and nickel resolved in the modern periodic table?
(c) Where should hydrogen be placed in the modern periodic table? Give reason for your answer.
Solution:
(a) Isotopes have the same atomic number but different atomic masses. Since the periodic table is based on atomic numbers, isotopes are not given separate positions.
(b) In Mendeleev’s periodic table, elements were arranged by increasing atomic mass. However, cobalt (atomic mass 58.9) was placed before nickel (atomic mass 58.7). In the modern periodic table, elements are arranged by atomic number, so cobalt (atomic number 27) comes before nickel (atomic number 28).
(c) Hydrogen is placed at the top of the periodic table because it has properties similar to both alkali metals and halogens. It is placed in Group 1 due to its electronic configuration, but its small size gives it unique properties.
19.v(a) On which side of the periodic table will you find metals?
(b) On which side of the periodic table will you find non-metals?
(c) What is the name of those elements which divide metals and non-metals in the periodic table?
Solution:
(a) Metals are on left side of the periodic table
(b) Non-metals are on right side of the periodic table
(c) Metalloids is the name of those elements which divide metals and non-metals in the periodic table.
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20. (a) Name three elements that have a single electron in their outermost shells.
(b) Name two elements that have two electrons in their outermost shells.
(c) Name three elements with completely filled outermost shells.
Solution:
(a) Lithium, Sodium, and Potassium are elements having a single electron in their outermost electron.
(b) Magnesium, Calcium has two electrons in the outermost shell
(c) Helium, Neon, and Argon are completely filled.
21. What is Dobereiner’s law of triads? Explain with the help of one example of Dobereiner’s triad.
Solution:
According to Dobereiner’s Law of Triads, when elements are arranged in increasing order of their atomic masses, they form groups of three with similar chemical properties, called triads. The atomic mass of the middle element is approximately the average of the atomic masses of the other two.
For example, calcium, strontium, and barium form a triad. Their atomic masses are 40, 88, and 137, respectively. The atomic mass of strontium (88) is close to the average of calcium and barium:
(40 + 137) ÷ 2 = 88.5
22. What is Newlands’ law of octaves? Explain with an example.
Solution:
According to the Newlands’ law of octaves, when elements are arranged in the order of increasing atomic masses, the properties of the eighth element (starting from a given element) are a repetition of the properties of the first element.
For example, Lithium is the first element having valence electron 1, and we find the eighth element from it is sodium having similar properties of lithium.
Benefits of Using Lakhmir Singh Solutions for Class 10 Chemistry Chapter 5
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Concept Clarity – Provides a clear understanding of the periodic classification of elements and their properties.
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Easy Explanation – Simple language and step-by-step solutions make learning easier.
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Exam-Oriented – Solutions are structured as per the latest CBSE syllabus, helping in effective exam preparation.
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Covers All Questions – Includes answers to all textbook exercises, important questions, and additional practice problems.
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Strengthens Problem-Solving Skills – Enhances analytical thinking with reasoning-based and numerical problems.
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Time-Saving – Helps students quickly grasp concepts and revise efficiently.
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Boosts Confidence – Encourages self-study and improves performance in exams.
