1. Atomic Structure

Dual Nature of Matter

The electrons which were treated to be particles, the evidence of photoelectric effect shows they also have wave nature. This was proved by Thomas young with the help of his double slit experiment.

De-Broglie concluded that since nature is symmetrical, so should be light or any other matter wave.

Quantum Numbers

  • Principal Quantum number (n): It denotes the orbital number or shell number of electron.
  • Azimuthal Quantum numbers (l): It denotes the orbital (sub-orbit) of the electron.
  • Magnetic Quantum number: It denotes the number of energy states in each orbit.
  • Spin Quantum number(s): It denotes the direction of spin, S = -½ = Anticlockwise and ½ = Clockwise.

Electronic Configuration of an Atom

The electrons have to be filled in the s, p, d, f in accordance with the following rule.

1. Aufbau’s principle: The filling of electrons should take place in accordance with the ascending order of energy of orbitals:

  • Lower energy orbital should be filled first and higher energy levels.
  • The energy of orbital α(p + l) value it two orbitals have same (n + l) value, E α n
  • Ascending order of energy 1s, 2s, 2p, 3s, 3p, 4s, 3d, . . .

2. Pauli’s exclusion principle: No two electrons can have all the four quantum numbers to be the same or if two electrons have to be placed in an energy state they should be placed with opposite spies.

3. Hund’s rule of maximum multiplicity: In the case of filling degenerate (same energy) orbitals, all the degenerate orbitals have to be singly filled first and then only pairing has to happen.

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