⚛️Periodic Table

About this tool

The standard 18-column table with lanthanides and actinides in the two rows below. Search by name, symbol or atomic number, click a category in the legend to highlight it, and click any element for its atomic number, standard atomic weight, category, period and group, with a copy button.

Reading the periodic table

Elements are arranged by atomic number — the number of protons — in rows called periods and columns called groups. Elements in the same group have the same arrangement of outer electrons and so behave alike: the alkali metals in group 1 react violently with water, the halogens in group 17 form salts, the noble gases in group 18 barely react at all. Moving across a period, metals give way to metalloids and then non-metals; the f-block lanthanides and actinides are drawn underneath so the table fits a page. Atomic weights here are IUPAC's abridged standard values — the averages you use in chemistry calculations; for elements with no stable isotopes, such as technetium and everything from polonium on, the bracketed figure is the mass number of the longest-lived known isotope. Category boundaries are debated in places (astatine is variously a halogen or a metalloid), and the chemistry of the superheavy elements from 104 onwards is mostly predicted rather than measured, since only a few atoms have ever been made. The molar mass calculator uses these weights for whole formulas, the scientific notation tool handles Avogadro-sized numbers, and the significant figures calculator rounds results.

Frequently asked questions