Electron arrangements and the periodic table
The The order electrons are arranged into between different energy levels. of an A substance made of one type of atom only. is related to its position on the periodic table.
| Electronic structure feature | Link to the periodic table |
| Number or numbers of shells | Period number |
| Number of electrons in outermost shell | Group number |
| Total number of electrons in all shells | Atomic number |
| Electronic structure feature | Number or numbers of shells |
|---|---|
| Link to the periodic table | Period number |
| Electronic structure feature | Number of electrons in outermost shell |
|---|---|
| Link to the periodic table | Group number |
| Electronic structure feature | Total number of electrons in all shells |
|---|---|
| Link to the periodic table | Atomic number |
The electron arrangement of sodium (2.8.1) shows that sodium, Na:
- is in period 3
- is in group 1
- has an The number of protons in the nucleus of an atom. Also called the proton number. of (2 + 8 + 1) = 11
The number of Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. shells is therefore the same across a period but increases when moving down a group.
Electron arrangements and properties of elements
The electron arrangements of The smallest part of an element that can exist. help explain the The characteristics of something. In chemistry, chemical properties include the reactions a substance can take part in. Physical properties include colour and boiling point. of elements and the structure of the periodic table. When substances react, it is only the outer electrons in the atoms that are involved - the nature of the reactions which occur depend upon the number of outer shell electrons in the reacting atoms.
So, elements in the same group have similar A description of how a substance reacts with other substances. For example, flammability, pH, reaction with acid, etc. because they have the same number of electrons in their outer shell.
The electron arrangements of the first three elements in group 1:
The atoms of all group 1 elements have similar chemical properties and reactions because they all have one electron in their outer shell. Similarly, the atoms of all group 7 elements have similar chemical properties and reactions to each other, because they all have seven electrons in their outer shell.
