NCERT Solutions for Class 10 Science Chapter 5

NCERT Solutions for Class 10 Science Chapter 5 – Periodic Classification of Elements, contains solutions to various questions in Exercises for Chapter 5. Periodic Classification of Elements Class 10 NCERT Solutions have been explained in a simple and easy to understand manner. We are providing NCERT Solutions for Class 10 all subjects which can be accessed by clicking here.

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

NCERT Solutions for Class 10 Science Chapter 5 – Periodic Classification of Elements, Exercises includes all in text and exercise solved questions which helps you to understand the topic covered in Chapter 5 Periodic Classification of Elements Class 10, in a better manner to help you to score good marks in your examinations.

NCERT Solutions for Class 10 Science Chapter 5 – Intext Questions – Page 81

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

Answer:

Yes, Döbereiner’s triads did exist in Newlands’ Octaves. The elements Lithium (Li), Sodium (Na), and Potassium (K) make a Döbereiner’s triad but are also present in the second column of Newlands’ octaves.

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

Answer:

The Döbereiner’s classification had limitations because:

  1. They did not apply for elements with very low mass or very high mass.
  2. The validity of these triads began to decrease with emerging methods of calculation of mass.
  3. Döbereiner’s triads could not accommodate all the elements present and the new elements that were being discovered.

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

Answer:

Newland assumed that there are only 56 elements in nature and did not consider discovery of new elements. The law is such that it is applicable only for elements till Calcium. It fits two elements in same slot and many elements with differing properties in same columns. For example, Iron (Fe) was placed far away from elements like Nickel and Cobalt, that share its properties.

Intext Questions – Page 85

1. Use Mendeléev’s Periodic Table to predict the formulae for the oxides of the following elements:

K, C, AI, Si, Ba.

Answer:

In Mendeléev’s Periodic Table, Oxygen is a member of group VI A making its valency two. According to the table, the formula for oxides of:

K is K2O, as K is the member of group I A with valency 1.

C is CO2 or C2O4, as C is a member of group IV A with valency 4.

Al is Al2O3, as Al is a member of group III A with valency 3.

Si is SiO2 or Si2O4, as Si is a member of group IV A with valency 4.

Ba is BaOor Ba2O2, as C is a member of group II A with valency 2.

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

Answer:

Besides gallium, Germanium and Scandium were also the elements that were later discovered and were left by Mendeléev in his Periodic Table.




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

Answer:

Mendeléev used the following criteria to sort elements in his Periodic Table:

  1. Elements were segregated on the basis of various compounds formed by them with Hydrogen and Oxygen.
  2. He also observed the relationship between atomic masses of the elements to distribute them across the table in various columns.

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

Answer:

Noble gases are placed in group zero. Due to their inert nature, they don’t react with other elements easily. Their concentration in our atmosphere is also low. In order to distinguish them and maintain the order of periodic table, they are placed in a separate group.

Intext Questions – Page 90

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

Answer:

The Modern Periodic Table removes the anomalies of Mendeléev’s Periodic Table by arranging the elements on the basis of atomic numbers. Since Mendeléev arranged his periodic table on the basis of atomic mass, the anomaly due to elements with same atomic mass are removed. The isotopes of same elements with different atomic masses are assigned with a fixed position in the modern periodic table. Also, atomic number of cobalt is 27 and nickel is 28, cobalt will come before nickel even though its atomic mass is greater.

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

Answer:

Calcium and Beryllium will have chemical reactions similar to magnesium. Both Calcium and Beryllium have two valence electrons and belong to the same group to which magnesium belongs to.

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.

Answer:

(a) Lithium (Li), Sodium (Na), Potassium (K).

(b) Magnesium (Mg), Calcium (Ca).

(c) Neon (Ne), Argon (Ar), Xenon (Xe).

4. (a) Lithium, sodium, 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?

Answer:

(a) Lithium, sodium and potassium are all alkali metals. They have only one electron in their outermost shell. This makes them highly unstable. They readily lose this electron and react with water to liberate hydrogen gas.

(b) Both helium and neon are noble gases. They have completely filled outermost electrons making them very stable and unreactive.

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

Answer:

Lithium (Li) and Beryllium (Be) are the metals among the first ten elements in 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

Answer:

In the given elements, Gallium and Beryllium have the maximum metallic characteristics. However, Gallium (Ga) has a larger size than beryllium so it loses its outermost electrons more easily making it the most metallic among the given compounds.

NCERT Solutions for Class 10 Science Chapter 5 – NCERT Exercise – Page 91

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.

Answer:

(c ) The atoms lose their electrons more easily.

We can say that this statement is incorrect because on moving left to right, the non-metallic character increases in elements. It becomes harder to lose electrons.




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

Answer:

(b) Mg (Mg has a valency of 2 and Cl has a valency of 1, so they form 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?

Answer:

(a) Neon

(b) Magnesium (atomic number 12)

(c) Silicon (atomic number 14)

(d) Boron (atomic number 5)

(e) Carbon (2,4)

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?

Answer:

(a) All the elements in the same column of the Periodic table as boron have the same valency of 3.

(b) All the elements in the same column of the Periodic table as fluorine have the same valency of 1. They gain one electron to complete their octet.

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)

Answer:

(a) 2+8+7 = 17.

Hence, the atomic number of this element is 17.

(b) Electronic configuration of:

N(7) = 2,5

F(9) = 2,7

P(15) = 2,8,5

Ar(18) = 2,8,8

Since Fluorine has the same number of valence electrons in its outermost shell as the given element, it would be chemically similar to it.

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

(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?

Answer:

Keeping the trends of the Periodic Table in mind, we can answer these questions.

(a) Element A is a non-metal.

(b) Element C is less reactive than A.

(c) C is smaller in size than B.

(d) A will form an anion. ( negative ion)

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?

Answer:

Electronic Configuration of:

Nitrogen: 2,5

Phosphorus: 2,8,5

As we move down the group in a periodic table the electronegativity of the elements decreases because of increasing distance between nucleus and outermost shell. So, Nitrogen will be more electronegative than phosphorus.

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

Answer:

The electronic configuration of an atom determines the number of valence electrons. Atoms with the same number of electrons in its valence shell are kept in the same group as they share similar chemical properties. Hence, electronic configuration helps decide the position of an element on the basis of its 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?

Answer:

The outermost shell of calcium has two electrons. Hence, the element with atomic number 12 with same number of valence electrons will have properties resembling to calcium.

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

Answer:

The Mendeléev’s Periodic Table and the Modern Periodic Table are different in the following ways:

Mendeléev’s Periodic Table and the Modern Periodic Table




Topics Covered in Periodic Classification of Elements Class 10 Science

  • Classification of Elements
    • Döbereiner’s Triads
    • Newlands’ Law of Octaves
  • MENDELÉEV’S PERIODIC TABLE
    • Achievements of Mendeléev’s Periodic Table
    • Limitations of Mendeléev’s Classification
  • Modern Periodic Table
    • Position of Elements in the Modern Periodic Table
    • Trends in the Modern Periodic Table
    • Trends in the Modern Periodic Table-Metallic and Non-metallic Properties
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