What is N+I rule?

N + I is called the Madelung Rule which is basically the order of filling and called the N + L rule. Here the n and I are quantum numbers that is used to specify the given electron orbital in the atom.

Here some facts about the Rule:

1. This is also called the Aufbau principle and it is named after German Aufbauprinzip which s actually the building up principle and it denotes that in the ground state of an atom or ion the electrons will fill up the atomic orbitals of the lowest energy level available before it goes to occupy the higher levels.
2. Let us take an example where the first sub shell is now filled and this happens before the second subtle fills and thus the electrons of the atom or ion will form stable electron configuration.
3. Let us study on the behaviour of the electrons here in this phenomenon. We know that electron behaviour is defined more in details by other principles of atomic physics like Hunds rule and so on. Hands rule say that the multiple orbitals of the same energy are there and electrons will now occupy the same orbitals in a single way before they are occupied in a double role. If we have double occupation the principles requires the electrons to occupy the same orbital but with different spins.
4. If we pass from element to next element with increasing atomic number then one proton and one electron are added each single time to the atom. The number of electrons which are maximum in nay shell is 2n2 where we can take the n as the principal quantum number. There are subtitles and having increasing electrons respectively and in the ground state this configuration is done by placing the electrons in the lowest place until and unless the electrons added is same to the atomic number.
5. The orbitals are filled up in the order of increasing energy and predicts the configuration of the electrons.These electrons are assigned in order of increasing value (N+I) . When we have sub shells with same number of electrons then the electrons are given to them with lowest value of N
6. The Aufbau principle also known as the nuclear shell model is also used for prediction for proton and neutron configuration in the atomic nucleus.

The Aufbau principle in the new quantum theory:

It was first formulated by Niels Bohr and Wolfgang Pauli in the 1920s. This was in the application of quantum physics and mechanics and it denoted the properties of the electrons and it did explain the process of the chemical reactions in physical terms. When we have one electron added and it is then subjected to the electric grid then we have an electric field and this is thus affected by the positive charges of the atomic nucleus and the negative charge of the electrons other than that and which are around and bound to the nucleus. However in the Hydrogen atom there is no known difference to the orbitals but it is not the same to the outer electrons of the other atoms.

In the old classical theory of quantum theory we have the mechanics where the electrons occupy the same elliptical orbitals and the orbits with highest angular momentum have circular shape which is outside the inner electrons but now the orbits who have lower angular momentum Which are the s and p orbitals have high orbitals and thus they are close to the nucleus and have strong nuclear charge.

Question: According to Aufbau principle the 19th electron in an atom goes into the :-

• 4s – orbital 2) 3d – orbital 3) 4p – orbital 5) 3p – orbital

The n + l energy ordering rule:

1. We take a periodic table where we have one row that corresponds to one value to n and l where n is the principal and l is the azimuthal quantum number Respectively.
2. This was given by Charles Janet in 1930
3. He said that the pattern which has a quantum basis which is based on atomic ground which we can find out by the analysis of atomic spectra.
4. He also adjusted some of the values of n and l and thus got that in the energy ordering rule he had some different values but which he said must be a result of some error in doing measures.
5. However when the n and l values that turned out to be correct it was just an approximation value and thus it denoted that the elements had low energy but were in excited state and were within chemical bond energies.
6. In the year 1936, The German physicist Erwin Madelung said this to be rule for calculating the order of filling up of atomic subtle and thereby came the Madelung Rule. It was also later said the sub shells should be