Periods and groups

Definition

The rows (periods) and columns (groups) of the periodic table, where periods mark the filling of a new electron shell and groups collect elements with matching valence configurations.

Moving left to right across a period increases atomic number and adds electrons to the same outer shell, changing behavior gradually and predictably. Elements in a group form ions of the same charge, bond similarly, and dissolve similarly. This is why Group 1 sodium and potassium are highly soluble and Group 2 calcium and magnesium form similar scales.

Related concepts

Valence electrons · Electron shells · Periodic Table

---

Part of The Blueprint of Water · 🧪 chemistry