Activity 1.5


1
Write the electronic configuration of elements from atomic number 11 to 18.

Ans:
Element
Symbol
Atomic Number
Shell Configuration
Electronic Configuration
K (2)
L (8)
M (18)
N (32)
Sodium
Na
11
2
8
1

2, 8, 1
Magnesium
Mg
12
2
8
2

2, 8, 2
Aluminium
Al
13
2
8
3

2, 8, 3
Silicon
Si
14
2
8
4

2, 8, 4
Phosphorus
P
15
2
8
5

2, 8, 5
Sulphur
S
16
2
8
6

2, 8, 6
Chlorine
Cl
17
2
8
7

2, 8, 7
Argon
Ar
18
2
8
8

2, 8, 8

2
What similarities do you find in their electronic configuration?

Ans:
Elements from atomic number 11 to 18 have the same number of electrons in their first two shells.

3
How many valence electrons are present in sodium, aluminum and chlorine?

Ans:
Element
Sodium
Aluminium
Chlorine
Valence Electrons
1
3
7

4
Write the electronic configuration of (i) Mg and Ca and (ii) F and Cl.

Ans:
Element
Mg
Ca
F
Cl
Electronic Configuration
2, 8, 2
2, 8, 8, 2
2, 7
2, 8, 7

5
Do these elements contain same number of valence electrons?

Ans:
  • Yes, magnesium and calcium contain the same number of valence electrons.
  • Also, Fluorine and chlorine contain the same number of valence electrons.
(Valence electrons: The number of electrons in the outermost orbit)

6
Write the electronic configuration of B, O, Na, Al, S and K.

Ans:
Element
Electronic Configuration
Boron (B)
2, 3
Oxygen (O)
2, 6
Sodium (Na)
2, 8, 1
Aluminium (Al)
2, 8, 3
Sulphur (S)
2, 8, 6
Potassium (K)
2, 8, 8, 1