We can represent the structure of the atom in two ways: using diagrams called electron shell diagrams or by writing out a special notation called the electronic configuration (or electronic structure or electron distribution)
Electron shell diagrams
Electrons orbit the nucleus in shells (or energy levels) and each shell has a different amount of energy associated with it
The further away from the nucleus, the more energy a shell has cause there are other weak forces which make them stay there not talking about the weak nuclear force.
Electrons fill the shell closest to the nucleus
When a shell becomes full of electrons, additional electrons have to be added to the next shell
The first shell can hold 2 electrons
The second shell can hold 8 electrons
For this course, a simplified model is used that suggests that the third shell can hold 8 electrons
For the first 20 elements, once the third shell has 8 electrons, the fourth shell begins to fill
The outermost shell of an atom is called the valence shell and an atom is much more stable if it can manage to completely fill this shell with electrons
The arrangement of electrons in shells can also be explained using numbers
Instead of drawing electron shell diagrams, the number of electrons in each electron shell can be written down, separated by commas
This notation is called the electronic configuration (or electronic structure)
E.g. Carbon has 6 electrons, 2 in the 1st shell and 4 in the 2nd shell
Its electronic configuration is 2,4
Electronic configurations can also be written for ions
E.g. A sodium atom has 11 electrons, a sodium ion has lost one electron, therefore has 10 electrons; 2 in the first shell and 8 in the 2nd shell
Its electronic configuration is 2,8
Electronic Configuration of Elements
Electron Shells & The Periodic Table
There is a clear relationship between the electronic configuration and how the Periodic Table is designed
The number of notations in the electronic configuration will show the number of occupied shells of electrons the atom has, showing the period in which that element is in
The last notation shows the number of outer electrons the atom has, showing the group that element is in (for elements in Groups I to VII)
Elements in the same group have the same number of outer shell electrons
