Tuesday, October 12, 2021

Periodic Classification of Elements | Class 10 | Activity 5.6 with Solution

Periodic Classification of Elements | Activities in Text Book with Solution

Activity 5.6

How do you calculate the valency of an element from its electronic configuration?

✅ Answer: 
  • Valency of metal: It is same as the number of valence electron.
  • Valency of non-metal: It is calculated by subtracting the number of valence electrons from 8. 
What is the valency of magnesium with atomic number 12 and sulphur with atomic number 16?

✅ Answer: 
  • Magnesium: 2, 8, 2. It is a metal. So valency= 2.
  • Sulphur: 2, 8, 6. It is a non-metal. So valency= 8-6 = 2 
Similarly, find out the valencies of the first twenty elements.

✅ Answer: 

Elements

Atomic No.

E. Config.

Valency

H

1

1

1

He

2

2

0

Li

3

2, 1

1

Be

4

2, 2

2

B

5

2, 3

3

C

6

2, 4

8 – 4 = 4

N

7

2, 5

8 – 5 = 3

O

8

2,6

8 – 6 = 2

F

9

2, 7

8 – 7 = 1

Ne

10

2, 8

8 – 8 = 0

Na

11

2, 8, 1

1

Mg

12

2, 8, 2

2

Al

13

2, 8, 3

3

Si

14

2, 8, 4

8 – 4= 4

P

15

2, 8, 5

8 – 5= 3

S

16

2, 8, 6

8 – 6= 2

Cl

17

2, 8, 7

8 – 7= 1

Ar

18

2, 8, 8

8 – 8= 0

K

19

2, 8, 8, 1

1

Ca

20

2, 8, 8, 2

2


How does the valency vary in a period on going from left to right?

✅ Answer: Valency first increases 1 to 4 then decreases from 4 to 0 (1, 2, 3, 4, 3, 2, 1, 0).

How does the valency vary in going down a group?

✅ Answer: Valency remains the same because valence electrons do not change on going down in a group.

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