Shell Diagrams & Electronic Configuration
Specification Point 1.19 (a):
Predict the electronic configurations of the first 20 elements in the periodic table as 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 then the more energy a shell has.
- Electrons occupy the shell closest to the nucleus which can hold only 2 electrons and which go in separately.
- When a shell becomes full electrons then fill the next shell.
- The second shell can hold 8 electrons and the third shell can hold eighteen electrons and the electrons organise themselves in pairs in these shells.
- 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 electron shells
Shell Diagrams & Electronic Configuration II
Specification Point 1.19 (b):
Predict the electronic configurations of the first 20 elements in the form: 2.8.1
- The arrangement of electrons in shells can also be explained using numbers called the electronic configuration.
- Lithium for example has 3 electrons, so its electronic configuration is 2, 1.
The Electronic configuration of the first twenty elements
Element Atomic number Electronic configuration
Hydrogen 1 1
Helium 2 2
Lithium 3 2,1
Beryllium 4 2,2
Boron 5 2,3
Carbon 6 2,4
Nitrogen 7 2,5
Oxygen 8 2,6
Fluorine 9 2,7
Neon 10 2,8
Sodium 11 2,8,1
Magnesium 12 2,8,2
Aluminium 13 2,8,3
Silicon 14 2,8,4
Phosphorus 15 2,8,5
Sulfur 16 2,8,6
Chlorine 17 2,8,7
Argon 18 2,8,8
Potassium 19 2,8,8,1
Calcium 20 2,8,8,2
Note: although the third shell can hold up to 18 electrons, the filling of the shells follows a more complicated pattern after potassium and calcium. For these two elements, the third shell holds 8 and the remaining electrons (for reasons of stability) occupy the fourth shell first before filling the third shell.
Number of Electrons & the Periodic Table
Specification Point 1.20:
Explain how the electronic configuration of an element is related to its position in the periodic table.
- There is a clear relationship between the outer shell electrons and how the Periodic Table is designed.
- The number of notations in the electronic configuration will show the number of 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.
The electronic configuration of chlorine as it should be written
The position of chlorine on the Periodic table which can be deduced from its electronic configuration
Edexcel GCSE Chemistry Notes
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Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.
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