Principles of Chemistry
The Periodic Table and Electronic Configuration
Pearson Edexcel International GCSE Chemistry
Arrangement of the Periodic Table
- The elements are arranged in order of increasing atomic number.
- Rows are periods; columns are groups, numbered 1 to 7 and 0.
Electronic configuration
- Electrons fill the shells from the inside out: the first shell holds up to 2 electrons, the second up to 8, and the third takes 8 before the fourth shell starts.
- Write the number of electrons in each shell, inner shell first, separated by full stops.
- Never write a charge on the electronic configuration of an atom.
Configuration and position
- For Groups 1 to 7, group number = the number of electrons in the outer shell.
- Period number = the number of shells: the number of shells determines the period.
Metals and non-metals
| Property | Metals | Non-metals |
|---|---|---|
| Electrical conductivity | good conductors of electricity | do not conduct electricity |
| Oxide | basic oxide | acidic oxide |
| Position | left of the staircase line | right of the staircase line |
Groups and noble gases
Elements in the same group have similar chemical properties because they have the same number of electrons in their outer shell.
The noble gases (Group 0) do not readily react:
- a full outer shell of electrons
- so the atom does not lose, gain or share electrons
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