CBSE Class 9 Answered

Distribution of Electrons in Orbits

• According to Bohr's model, electrons occupy certain stable orbits or shells. Each shell has definite energy.
• These orbits or shells are represented by the letters K, L, M, N, ...  or  the numbers 1, 2, 3, 4, …
• The maximum number of electrons present in the shell is given by the formula (2 n²), where n is the orbit number or shell number.
• The maximum numbers of electrons in different shells are as follows:

• The first orbit or K shell will have 2 × 1² = 2 electrons.
• The second shell will have 2 × 2² = 8 electrons.
• The third shell will have 2 × 3² = 18 electrons.
• The fourth shell will have 2 × 4² = 32 electrons and so on.

• The maximum number of electrons that can be accommodated in the outermost orbit is 8.
• The orbits or shells are filled in a step-wise manner.
• Electrons are not accommodated in a given shell unless the inner shells are filled.