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Why does the 4s orbital get filled before the 3d orbital |
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Answer» Aufbau Principle suggests that the electrons be FILLED into different orbitals in the increasing order of energy STARTING with the ORBITAL with the lowest energy. Relative energies of VARIOUS orbitals is given by (n+l) Rule. Here lesser the value for (n+l), lesser will be the energy. And the one with lesser energy gets filled first according to Aufbau Principle. For 4s - n = 4 , s = 0 , (n+l) = 4FOR 3d-n = 3 , d= 2 , (n+l) = 5 Hence 4s is filled first. Remember the values of 'l' for orbitals s = 0 p = 1d = 2 f = 3 |
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