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.