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Write a note on ‘Principal Quantum number.

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Question

Write a note on ‘Principal Quantum number.

Answer in Brief
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Solution

Principal quantum number (n):

  1. Principal quantum number indicates the principal shell or main energy level to which the electron belongs.
  2. It is denoted by ‘n’ and is a positive integer with values 1, 2, 3, 4, 5, 6, ….
  3. A set of atomic orbitals with a given value of ‘n’ constitutes a single shell. These shells are also represented by the letters K, L, M, N, etc.
  4. With an increase of ‘n’, the number of allowed orbitals in that shell increases and is given by n2.
  5. The allowed orbitals in the first four shells are given below:
    Principal quantum number (n) Shell symbol Allowed number of orbitals (n2) Size of shell
    1 K 1 ↓ increases
    2 L 4
    3 M 9
    4 N 16
  6. As the value of ‘n’ increases, the distance of the shell from the nucleus increases, and the size of the shell increases. Its energy also goes on increasing.
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Chapter 4: Structure of Atom - Exercises [Page 54]

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Balbharati Chemistry [English] Standard 11 Maharashtra State Board
Chapter 4 Structure of Atom
Exercises | Q 6. (Q) | Page 54

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