The Number of Valence Electrons
The number of valence electrons of an element is determined by its periodic table group (vertical column) in which the element is categorized. With the exception of groups 3–12 (the transition metals), the number within the unit's place identifies how many valence electrons may be associated with an atom of an element listed under that particular column.
| Periodic table group | Valence electrons |
|---|---|
| Group 1 (I) (alkali metals) | 1 |
| Group 2 (II) (alkaline earth metals) | 2 |
| Groups 3-12 (transition metals) | See note * |
| Group 13 (III) (boron group) | 3 |
| Group 14 (IV) (carbon group) | 4 |
| Group 15 (V) (pnictogens) | 5 |
| Group 16 (VI) (chalcogens) | 6 |
| Group 17 (VII) (halogens) | 7 |
| Group 18 (noble gases) | 8** |
* The general method for counting valence electrons is generally not useful for transition metals. Instead the modified d electron count method is used.
** Except for helium, which has only two valence electrons.
Read more about this topic: Valence Electron
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