We all learned in Basic Chemistry Course/Syllabus such as GCE-O Levels Chemistry that elements are found in the electron shell(s) and each shell can only accommodate up to a maximum of electrons.
This is what you might have learned previously:
- Shell 1 – Maximum of 2 Electrons
- Shell 2 – Maximum of 8 Electrons
- Shell 3 – Maximum of 8 Electrons
- Shell 8 – Maximum of 8 Electrons etc etc
As such, you would have heard previously that all elements can only hold 2 or 8 electrons in their valence shell – terms such as Duplet and Octet structure exists.
And the Electronic Configurations for Sodium (Ar=11) would be 2.8.1.
Now, when you come to doing Advanced Level Chemistry such as GCE A-Level Chemistry, we are going to learn a little more in depth, and perhaps what you learned in Basic Chemistry Course would not be so true now.
Let’s see what is new and additional!
Electron shells are also known as Principal Quantum Numbers i.e. first shell has principal quantum number = 1
Each electron shell consists of a number of Sub-Shells, labelled s, p, d or f.
The number of sub-shells in each shell equals to the shell number i.e. 1st shell has 1 sub-shell and 2nd shell has 2 sub-shells, etc
Each sub-shell contains a number of Orbitals. in which the electrons are placed. The number of orbitals in each sub-shell depends on the type of sub-shell as shown below:
| Type of Sub-Shell | Number of Orbitals |
| s | 1 |
| p | 3 |
| d | 5 |
| f | 7 |
Each of this orbitals can each take up 2 electrons.
Let’s take a look at an YouTube video now to have a better understanding on the connections between principal quantum shells, sub-shells, types of orbitals and the maximum number of electrons which can be occupied.
Length of video: 3.48 minutes
Direct video link: https://www.youtube.com/watch?v=xXdlAv-SO7c&t=1s
Stay tuned for next blogpost for Part 2 of Electronic Configuration of Atoms!