NCERT Question 9 - Chapter 4 Class 9 - Structure of Atom

Na ⁺ has completely filled K and L shells. Explain.

Answer

Na ⁺ is an ion having a positive charge of +1

Positive charge of +1 indicates that the ion has 1 less electron than the stable neutral atom.

We know that,

Atomic number of Na (Sodium) = 11

That is, number of electrons in outer shell of Na = 1

Electronic configuration of Na is as follows:

K shell = 2 e ^-

L Shell = 8 e ^-

M Shell = 1 e ^-

Na ⁺ has 1 less electron than Na.

Therefore, number of electrons in Na ⁺ = 11 - 1 = 10 e ^-  

Electronic configuration of Na ⁺ is as follows:

K shell = 2 e ^-

L Shell = 8 e ^-

Now K and L Shell can contain maximum 2 and 8 electrons respectively. ( 2n ² rule)

Hence, they have completely filled K and L shells with 10 electrons .