Question

The orbital diagram which violates the “Aufbau’s principle” is?

Answer 1

To be able to tell which of the following orbitals violate aufbau’s principles, we must know what aufbau’s principle is. Many laws were made regarding the filling of the electrons in the shells, subshells and orbitals like (n+l) rule, aufbau’s principle, hund’s rule of multiplicity and pauli’s exclusion principle.

Complete step by step solution:
-After a lot of experiments, atomic structure was proposed and the probability of electrons were found to be maximum in a space known as orbital. Based on further studies, 4 quantum numbers were proposed which were able to give a complete picture of the electron location.
-Principle quantum number represents the shell of the electrons. It is represented by n. It gives a complete picture of shells and also the number of sub-shells. Value of n is always in natural numbers. First shell is denoted as K, second as L, third as M and fourth as N. Number of subshells is given by value of n and of orbitals by ${{n}^{2}}$ .
-Next is azimuthal quantum number denoted as l. It tells about the subshell and the number of orbitals. It starts from 0 and continues till (n-1). It also gives us the shape of the orbitals. The number of orbitals lie in the range from (-l to +l) as integers.
-Third quantum number is magnetic quantum number and is denoted by m. It gives us the exact orbitals. Its total value can be given as ${{n}^{2}}$ or as (2l+1) since it lies in the range (-l to +l).
-Last quantum number is spin quantum number which tells us about the spin of an electron in the orbital. It is denoted as s. It has only 2 values, +0.5 and -0.5. If the orientation is clockwise, then the spin is positive or negative.
-After studying about the orbitals, rules were made so as to fill the electrons in those orbitals. Aufbau stated a law after certain experiments. There were 3 rules for electronic configuration.
1. (n+l) rule – It tells us in which subshell the electron goes first. Electrons enter in that subshell first which has the least value of n+l. This is because that subshell has the lowest energy level.
2. Hund’s rule of maximum multiplicity – Electrons are placed so as to obtain maximum multiplicity which is obtained by putting electrons of the same spin in different orbitals.
3. Pauli’s exclusion principle – It stated that no 2 electrons can exist with all 4 same quantum numbers.
-So, if we follow these rules, then we can see that option A is incorrect as it disobeys Hund’s rule of multiplicity. Option B disobeys the (n+l) rule. Electrons are first filled in the s subshell and not in the p subshell. Option C and D both follow the rules. So they are correct.

Thus the correct options are C and D.

Note: Many elements do not follow this law and so their configuration is different from that depicted by the law. Lanthanoid and actinoid series do not follow this law. Also elements like Nb, Cu, Cr, Mo, Tc, Ru, Rh, Pd, Ag, Au, Pt do not follow this law.