Question 4.
Write down the electronic configuration of the following elements from the given atomic numbers. Answer the following question with explanation.
3Li, 14Si, 2He, 11Na, 15P
Which of these elements belong to be period 3?
Answer:
Electronic configuration:
⇒ The atomic number of lithium = 3
The electronic configuration of 3Li = 2,1
⇒ The atomic number of silicon = 14
The electronic configuration of 14Si = 2,8,4
⇒ The atomic number of helium = 2
The electronic configuration of 2He = 2
⇒ The atomic number of sodium = 11
The electronic configuration of 11Na = 2,8,2
⇒ The atomic number of phosphorus = 15
The electronic configuration of 15P = 2,8,5
Among the given elements, Na(2,8,2), Si(2,8,4) and P(2,8,5) belong to group 3. Because in these elements, total three shells are present. Thus, these elements belong to group 3.
