List the order in which the orbitals are filled as the atoms beyond hydrogen are built up. How many electrons overall can be accommodated in the first and second principal energy levels? How many electrons can be placed in a given s subshell? In a given p subshell? In a specific p orbital? Why do we assign unpaired electrons in the 2p orbitals of carbon, nitrogen, and oxygen?

Interpretation:

The order in which the orbitals are filled as the atoms beyond hydrogen are built up should be determined. The maximum number of electrons that can be accommodated by the first and second principle energy levels based on the number of electrons that can occupy a single atomic orbital should be determined. In addition, one must specify the presence of unpaired electrons in C, N and O atoms.

Concept Introduction:

Aufbau principle which in German means building up specifies the way how electrons are filled to the orbitals. It specifically states that the filling begins with the sublevel in lowest energy and continues upwards.

Pauli Exclusion Principle limits the number of electrons that could be accommodated in a single orbital.

Aufbau principle states the order in which electrons are filled to the orbitals. The basis for this is that “the filling begins with the sublevel lowest in energy and continues upwards accordingly. This order can be represented as follows:

1s→2s→3s→2p→3p→4s→3d→4p→5s→4d→5p→6s→4f→5d→6p→7s→5f→6d

The direction of the arrows starting from 1s shows the order in which electrons are filled to the sublevels.

The first principle energy level has only one s orbital (designated as 1s). The total number of electrons that a given orbital can occupy is two. Hence first principle energy level can accommodate only two electrons

The second principal energy level has a single s orbital (2s) and three p orbitals (designated as 2p_x, 2p_y and 2p_z ). This gives 4 total atomic orbitals for the second principle energy level. The total number of electrons that a given orbital can occupy is two. Hence the total number of electrons that the second principle energy level can accommodate is 8

According to Pauli Exclusion Principle an atomic orbital cannot hold more than two electrons, and the two electrons should have opposite spins.

Hence this imposes a restriction on the number of electrons as well as the way how their spins must be arranged