NCERT Solutions for class 10 Science Chapter 5: Periodic Classification of Elements

NCERT Solutions for class 10 Science Chapter 5 Exercise Question

Question 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.

Question 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:

(b) Mg

Question 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 (2, 8, 2)

c) Silicon

d) Boron

e) Carbon

Question 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) The elements present in same column as boron have three electrons in valence shells.

(b) All elements in the same column as fluorine will have a valency of 1. .Also non-metals and are highly electronegative in character

Question 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)The atomic number of element (2+8+7) is 17 ,So its chlorine.

(b) it has 7 valence electrons, therefore it would be chemically similar to F(9)=2,7

Question 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

A is a non-metal
C is less reactive than Element A
C is smaller in size than B
A will form anion

Question 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

Atomic number of Nitrogen is 7
Electronic configuration 1s 2 ,5

Atomic number of phosphorus is 15
Electronic configuration 1s 2,8,5

Outermost shell of Nitrogen is nearest to nucleus ,a strong force of attraction act on electron also electron attracting tendency decreases When we move from top to bottom in group .So Nitrogen is more electronegative than phosphorus.

Question 8

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

Answer

Electronic configuration of an atom gives valence electrons and number of shell present in the atom. By using valence electrons We get the information of group and we get information of period with help of shells present in an atom as the number of shells present in an eatom is equal to the period number. For example
if an element has 3 or 4 electrons in its outermost shell, then it belong to group 3 or group 4.

Question 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

Electronic configuration atomic number 12 = 2, 8, 2
Electronic configuration atomic number 19 = 2, 8, 8, 1
Electronic configuration atomic number 20 = 2, 8, 8, 2
Electronic configuration atomic number 21 = 2, 8, 9, 2
Electronic configuration atomic number 38 = 2, 8, 18, 8, 2

Calcium has 2 valence electrons. The velency electrons of the element having atomic number 12 and 38 is 2, and this element with 2 valence electrons have physical and chemical properties resembling calcium.

Question 10

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

Answer