Valence Electrons Periodic Table
For any main-group element, the periodic table tells you its valence electron count directly from its group number.
| Groupe | Électrons de valence | Examples |
|---|---|---|
| Groupe 1 | 1 | Li, Na, K |
| Groupe 2 | 2 | Be, Mg, Ca |
| Groupe 13 | 3 | B, Al, Ga |
| Groupe 14 | 4 | C, Si, Ge |
| Groupe 15 | 5 | N, P, As |
| Groupe 16 | 6 | O, S, Se |
| Groupe 17 | 7 | F, Cl, Br |
| Groupe 18 | 8 | Ne, Ar, Kr (He has 2) |
How to find valence electrons by hand
- Find the element's group (column) number on the periodic table.
- Groups 1 and 2: the valence electron count equals the group number (1 or 2).
- Groups 13–18: subtract 10 from the group number (group 17 → 17 − 10 = 7 valence electrons).
- Helium is the one exception in group 18: it has only 2 valence electrons, not 8, because its first shell holds at most 2.
Exemple résolu
Nitrogen is in group 15. Subtracting 10 gives 15 − 10 = 5 valence electrons — matching the 3 bonds and 1 lone pair nitrogen typically forms, as in ammonia (NH₃).
Build an atom's full electron shell structure in the Laboratoire d'Électronique below, or look up any element's details on the periodic table.
Foire aux questions
What are valence electrons?
The electrons in an atom's outermost shell — the ones involved in bonding with other atoms. They decide how an element reacts.
How do you find the number of valence electrons from the periodic table?
For main-group elements (groups 1, 2 and 13–18), the group number gives it directly: groups 1–2 have 1–2 valence electrons, and groups 13–18 have (group number − 10) valence electrons.
How many valence electrons does oxygen have?
Six. Oxygen is in group 16, and 16 − 10 = 6.
Why don’t transition metals follow the simple group rule?
Transition metals (groups 3–12) can lose electrons from more than one shell, so their valence electron count depends on which ion they form rather than a fixed group rule.
