Atomic Structure - Aufbau Principle

Writing electronic configuration of the various elements require us to make use of the Aufbau Principle. This is because it is not all the electrons found in the principal quantum shell have the same amount of energy.

In each principal quantum shell (except when n=1), there are subshells. These subshells do not have the same energy level. Hence, they are not filled at the same time.

Below is the video which summaries the different energy level as well as a short description to how Aufbau Principle works. This video will make use of nitrogen and manganese to demonstrate how the principle works in the writing of electronic configuration.


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^{Article written by Kwok YL 2011.}

^{Disclaimer and remarks:}

• ^{If you would like to use this source, kindly drop me a note by leaving behind a comment with your name and institution. I am all for sharing as the materials on this blog is actually meant for the education purpose of my students.}
• ^{This material is entirely written by the author and my sincere thanks will be given to anyone who is kind, generous and gracious to point out any errors.}

Atomic Structure - Energy Level

In the study of atomic structure, there is a certain set of ground rules (please refer to lecture material for basics) which we make use to fill electrons. These rules are formulated because we fill electrons in shells, subshells and orbital which are of lower energy level first.

The following diagram illustrates the three main orbital which we are required to know at the GCE "A" Level curriculum. Of these three orbitals, the s-orbital has the lowest energy while the d-orbital has the highest.

This electrostatic attraction will result in the s-orbital to be of lower energy. This is abit perplexing, but we need to rationalise that electrostatic attraction is a form of potential energy (PE).

By definition, potential energy is a negative number and the weakest potential energy is at infinity. In that case, PE = 0. Hence, a greater electrostatic attraction will result in a larger numerical value of PE, but because of the definition of PE, the energy is lowered.
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Article written by Kwok YL 2009.}

^{Disclaimer and remarks:}

• ^{If you would like to use this source, kindly drop me a note by leaving behind a comment with your name and institution. I am all for sharing as the materials on this blog is actually meant for the education purpose of my students.}
• ^{This material is entirely written by the author and my sincere thanks will be given to anyone who is kind, generous and gracious to point out any errors.}

Atomic Structure - Introduction

The basic idea of the structure of an atom is that it contains protons and neutrons which make up the nucleus and electrons which circulate around the nucleus. In basic courses of chemistry, one learns that electrons are filled in shells and each shell encircles the nucleus, hence giving an atomic structure which is shown below.

Hence, if we examine the energy required to remove successive electron of an atom we will obtain a linear graph as depicted below. The increasing graph shows that it becomes increasing difficult to remove an electron from a particle which is increasing positive.

The graph will be coherent to the above model of a structure of an atom. That is because the electrons in a particular shell receives the same electrostatic attraction from the nucleus. (P.S. energy to remove an electron is known as ionisation energy).

However, the actual graph showing the ionisation energies of the atom is shown below. The graph shows that the removal of the 11th and 12th electron is more difficult than the earlier electrons and that using the reason "removal of an electron from a particle which is getting more positive" is insufficient. Hence, this implies that the 11th and 12th electron are closer to the nucleus than the 13th to the 18th electron.

Hence, the concept of orbital and subshell is conceived. The orbital is the area where the electrons are found. In the A level syllabus, we focus on three types of orbitals, (i) s, (ii) p and (iii) d. Their illustration is shown below and each orbital can only occupy a maximum of two electrons.

Therefore, there is the idea of subshell; where each subshell contains a number of orbtial. The s-subshell contains just one s orbital, while the p-subshell contains three p orbital and the d-subshell contains five d orbtial.

This idea of atomic structure is the correct interpretation of the atomic structure and it allows for us to account for the ionisation energies of the atom.

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Article written by Kwok YL 2009.}

^{Disclaimer and remarks:}

• ^{If you would like to use this source, kindly drop me a note by leaving behind a comment with your name and institution. I am all for sharing as the materials on this blog is actually meant for the education purpose of my students.}
• ^{This material is entirely written by the author and my sincere thanks will be given to anyone who is kind, generous and gracious to point out any errors.}