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Atomic Structure - Postulates of Bohr's Theory of Atom

Grade 7CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Electrons revolve around the nucleus in fixed circular paths called 'orbits' or 'shells'.

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Each orbit is associated with a fixed amount of energy, which is why they are also called energy levels or stationary states.

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These shells are represented by the letters K,L,M,N,…K, L, M, N, \dots or the numbers n=1,2,3,4,…n = 1, 2, 3, 4, \dots starting from the nucleus.

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While revolving in these discrete orbits, electrons do not radiate energy, ensuring the atom remains stable.

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The maximum number of electrons that can be accommodated in any shell is determined by the formula 2n22n^2.

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Energy is emitted or absorbed only when an electron jumps from one energy level to another: ΔE=Efinal−Einitial\Delta E = E_{\text{final}} - E_{\text{initial}}.

📐Formulae

Maximum electrons in a shell=2n2\text{Maximum electrons in a shell} = 2n^2

n=1(K),2(L),3(M),4(N),…n = 1 (K), 2 (L), 3 (M), 4 (N), \dots

ΔE=E2−E1\Delta E = E_2 - E_1

💡Examples

Problem 1:

Calculate the maximum number of electrons that can be accommodated in the MM shell of an atom.

Solution:

For the MM shell, the orbit number is n=3n = 3. Using the formula 2n22n^2: 2×(3)2=2×9=182 \times (3)^2 = 2 \times 9 = 18

Explanation:

According to Bohr's theory, the third shell (MM shell) can hold a maximum of 1818 electrons.

Problem 2:

Identify the shell represented by n=2n = 2 and calculate its electron capacity.

Solution:

The shell for n=2n = 2 is the LL shell. Its capacity is: 2×(2)2=2×4=82 \times (2)^2 = 2 \times 4 = 8

Explanation:

The second shell from the nucleus is the LL shell, which can hold up to 88 electrons.