What are 'energy levels'? Explain the arrangement and distribution of electrons in the various shells with reference to an atom in general and to an atom of potassium with special reference to the 2n² rule.

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KnowledgeBoat · Accepted Answer

Electrons revolve around the nucleus in fixed orbits. Each orbit is associated with a certain amount of energy hence named 'energy levels'. Arrangement of electrons : - The shell closest to the nucleus is called K shell [first shell or number one shell]. - The next shell is called the L shell [second shell or number 2 shell] - Following shells are M,N...etc. - An electron has minimum energy in the first or K shell and the energy increase in the order K, L, M, N. - The maximum number of electrons which can be present in any shell of an atom is given by or represented by a formula 2n², where n is equal to the number of the shell as counted from the nucleus. Shell | Shell
No.[n] | Formula
2n² | Max
Electrons ----- | ---------------- | ------------------------- | ---------------- K | 1 | 2 × (1)² | 2 L | 2 | 2 × (2)² | 8 M | 3 | 2 × (3)² | 18 N | 4 | 2 x (4)² | 32 - The outer most shell cannot have more than 8 electrons. - The penultimate shell [last but one ] cannot have more than 18 electrons. - A new shell is formed as soon as the - outermost shell attains 8 electrons. With reference to Potassium : No. of Electrons [e] = 19 No. of Protons [p] = 19 No. of Neutrons [n] = A - Z = 39 - 19 = 20 The two rules governing the distribution of electrons are: 1. Rule 1 — Maximum number of electrons in each shell is given by the formula 2n² 2. Rule 2 — The outermost shell cannot have more than 8 electrons. As per rule 1 (2n² rule), distribution of electrons for Potassium will be: Shell | Electrons ----- | --------- K | 2 L | 8 M | 9
[Last Shell] But as per rule 2, outermost shell cannot have more than 8 electrons. So M shell will have 8 electrons and a new shell (N) will be formed with 1 electron. Hence, the final electronic configuration of Potassium will be: Shell | Electrons ----- | --------- K | 2 L | 8 M | 8 N | 1 ∴ Electronic configuration of Potassium = 2, 8, 8, 1

Chemistry

What are 'energy levels'? Explain the arrangement and distribution of electrons in the various shells with reference to an atom in general and to an atom of potassium with special reference to the 2n<sup>2</sup> rule.

Atomic Structure

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