ICSE Class 7 Answered

Rules given by Bohr - Bury for distribution of electrons:

• According to Bohr’s model, electrons occupy certain stable orbits or shells. Each shell has a 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 (2n²), where n is the orbit number or shell number.
• The maximum number of electrons in different shells is 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 which 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.