NCERT Solutions for Class 10 Science Chapter 5

NCERT Solutions for Class 10 Science Chapter 5 Periodic Classification of elements intext questions on Page 81 or Page 85 or Page 90 or Exercises in English updated for new academic session 2020-2021 free for all. NCERT Solutions given on पेज 91 or पेज 94 or पेज 100 or अभ्यास के प्रश्न उत्तर in हिंदी मीडियम are also given to view online or download in PDF form for all boards who are using NCERT Books 2020-21. Download Offline Solutions Apps 2020-21 to use without internet, free of cost.

NCERT Solutions for Class 10 Science Chapter 5

Class: 10Science – विज्ञान
Chapter 5:Periodic Classification of elements

10th Science Chapter 5 Answers in English & Hindi Medium

NCERT Solutions for class X Science all chapter are in PDF updated for new academic session 2020-21. Online view is also being provided for the convenience of students. 10th Science Chapter 5 Periodic Classification of elements all intext questions and exercises questions are given below.

Write two reasons responsible for the late discovery of noble gases.

(a) Noble gasses are inert.
(b) These are present in nature in minute amounts.

State Modern Periodic Law. What is the Modern Periodic Table called?

Modern Periodic Law : the physical and chemical properties of elements are the function of their atomic numbers. The Modern Periodic Table is called ‘long form’ of the periodic table.

Metals have tendency to form cations. Why?

As the effective nuclear charge on the valence electrons in the metals is comparatively less, they have tendency to form cations.

Why is Fluorine atom smaller than chlorine atoms?

Fluorine atom is smaller than chlorine atom as it has less number (2) of shells compared to that in chlorine (shells 3).

Given reason why Non-metals have tendency to gain electrons?

Non-metals have high nuclear attraction on the outermost shells and thus these have tendency to attract/gain electrons.

Questions for Practice

Question 1:
What are the discrepancies in Mendeleev’s periodic table?
Or
List two observations which posed a challenge to Mendeleev’s Periodic law.
Answer 1:
(i) Position of isotopes: Isotopes of various elements cannot be filled into Mendeleev’s table. Isotopes are the elements having similar chemical properties but different atomic masses.
(ii) Anomalies of atomic weights and properties of elements: If arranged according to gradation in chemical properties, elements of higher atomic weights are to be placed before those of lower atomic weights at some place. This is contrary to Mendeleev’s law. For example, argon with atomic mass of 40 comes before potassium with atomic mass 39. Iodine (at. mass = 127) comes after tellurium (at. mass = 127.8).
(iii) Falling of dissimilar elements in same group: Some chemically similar elements fall in different group chemically dissimilar elements are placed together. For example, copper, silver and gold are placed in the same group with alkali metals. Mercury, lead and barium which possess similar properties fall into different groups.
(iv) Hydrogen resembles both alkali metals (group I) and halogens (group VII) and thus no fixed position could be given to hydrogen in the periodic table.

Question 2:
Mention the position of (i) hydrogen and (ii) isotopes of same element in the modern periodic table.
Answer 2:
(i) Hydrogen is placed at the top of group IA.
(ii) Isotopes of the same elements are placed in the same slot.

Questions from Board Papers

Question 1:
Why is atomic number of an element more important to a chemist than its atomic mass?
Or
Atomic number is considered to be a more appropriate parameter than atomic mass for classification of elements in a periodic table. Why?
Answer 1:
The properties of element depend upon the number of electrons present in the valence shell which are related to atomic number. Thus the properties of different elements can be compared if we know their atomic numbers. On the other hand, atomic mass can in no way determine the chemical properties of elements, because is does not vary regularly with gradation in the chemical properties of elements.

Question 2:
The atomic number of an element ‘X’ is 20. Write
(a) its valency,
(b) whether it is a metal or non-metal,
(c) the formula of compound formed when the element ‘X’ reacts with an element ‘Y’ of atomic number 8.
Justify your answer in each case.
Answer 2:
(a) Electronic configuration of X is 2, 8, 8, 2. Its valency is 2.
(b) It is a metal. It belongs to group 2 and can lose 2 electrons easily.
(c) Formula of compound of X and Y is XY. Since valency of Y is -2 (2, 6).

Question 3:
The element Li, Na and K, each having one valence electron, are in period 2, 3 and 4 respectively of Modern Periodic Table.
(a) In which group of the periodic table should they be?
(b) Which one of them is least reactive?
(c) Which one of them has the largest atomic radius? Give reason to justify your answer in each case.
Answer 3:
(a) Group 1. These all have one valency.
(b) Li. Its outermost orbit is very near to the nucleus and so removal of electron is a little difficult.
(c) K has largest atomic radius. It occupies three shells.

Important Questions on 10th Science Chapter 5

What property do all elements in the same column of the Periodic Table as boron have in common?
All the elements in the same column as boron have the same number of valence electrons (3). Hence, they all have valency equal to 3.
What property do all elements in the same column of the Periodic Table as fluorine have in common?
All the elements in the same column as fluorine have the same number of valence electrons (7). Hence, they all have valency equal to 1.
How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?
In the modern periodic table, atoms with similar electronic configurations are placed in the same column. In a group, the number of valence electrons remains the same. Elements across a period show an increase in the number of valence electrons.
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?
The element with atomic number 12 has same chemical properties as that of calcium.

This is because both of them have same number of valence electrons (2).

What were the limitations of Dobereiner’s classification?
Limitation of Dobereiner’s classification were as follows:
All known elements could not be classified into groups of triads on the basis of their properties. Only few triads were made.
What were the limitations of Newlands’ Law of Octaves?
Limitations of Newlands’ law of octaves:
a) It was not applicable throughout the arrangements. It was applicable up to calcium only. The properties of the elements listed after calcium showed no resemblance to the properties of the elements above them.
b) Those elements that were discovered after Newlands’ octaves did not follow the law of octaves.
c) The position of cobalt and nickel in the group of the elements (F, Cl) of different properties could not be explained.
d) Placing of iron far away from cobalt and nickel, which have similar properties as iron, could also not be explained.
What were the criteria used by Mendeleev in creating his Periodic Table?
Mendeleev’s periodic table was based on the observation that the properties of elements are a periodic function of their atomic masses. This means that if elements are arranged in the increasing order of their atomic masses, then their properties get repeated after regular intervals.
Why do you think the noble gases are placed in a separate group?
Noble gases are inert elements. Their properties are different from the all other elements. Therefore, the noble gases are placed in a separate group.

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