12/23/2023 0 Comments Aufbau principle sentenceHund’s rule, Aufbau Principle, Pauli Exclusion Principle It is used to determine the electronic configuration of an atom or ion.It explains the manner in which the electrons are filled in the orbital.In the context of copper, the correct electronic configuration is 3d 104s 1 rather than 3d 94s 2.This is due to the reason that Cu shifts its one 4s electron to 3d so that the 3d orbitals get fully filled.Īs we know that half-filled and full-filled orbitals possess greater stability, the electronic configuration 3d 104s 1 is more stable, and therefore correct than the expected electronic configuration of copper 3d 94s 2. But the correct electronic configuration of chromium that shows deviation from the principle us 3d 54s 1.Īs we know that half-filled and full-filled orbitals possess greater stability, the expected electronic configuration does not possess half-filled or full-filled orbital, while the correct configuration on shifting its one 4s electron to 3d electrons ( 3d 54s 1 ) acquires half-filled orbital, and is, therefore, the stable configuration than 3d 44s 2. In the case of Chromium, the expected electronic configuration is 3d 44s 2. One of the common elements that show exceptions to this principle is Chromium and Copper. The fully-filled or half-filled orbitals possess greater stability. This deviation/exception is due to the shifting of an electron from its ns orbital to (n-1)d orbital to achieve fully-filled or half-filled orbitals. Some of the elements show quite much deviation from this principle. Now, the electronic configuration of Chlorine according to the Principle is 1s 22s 23p 64s 23p 5 Aufbau Principle Violation/Exception/Limitations Thus, the electrons are filled in the increasing order of energy levels. Then, the remaining five electrons occupy at 3p orbitals which have (n+ l) value of 4. In such cases, the orbital with a low ‘n’ value is filled first, and hence 3s orbital is filled after 2p orbital. 3s orbitals are filled after 2p orbital though both have the same (n+l) value of 3. Then electron will occupy at 2s orbital having (n+l) value of 2, and then to the 2p orbital which has 3 ( (n+l) value. According to this Principle, as well as Hund’s rule and Pauli exclusion principle, the first two-electron will occupy in 1s orbital as this orbital possesses the lowest (n+l) value of 1. Let us write the electronic configuration of Chlorine (Cl).Ĭhlorine has an atomic number of 17, which means that it possesses 17 electrons. This is the reason, 2 p orbital is filled first before 3 s orbital. Thus the factor 2 explained above operates and the orbital with the lowest ‘n’ value gets filled first. In the case of 2p and 3s orbitals, both have same (n+ l ) value i.e. After filling of 1s orbital, electrons will be consequently filled in 2s, 2p, 3s, and so on. The diagram given below explains the correct sequence of filling up of energy levels.Īs shown in the figure, electrons will be first filled in 1s orbital as it possesses the lowest (n+ l ) value.
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