Periodic Table

This interactive periodic table covers all 118 elements confirmed by IUPAC. Select any element to see its atomic number, standard atomic weight, electron configuration, category, period and group, electronegativity, first ionization energy, atomic radius, density, melting and boiling points, state at room temperature and who discovered it, along with a simple sketch of its electron shells.

Search by name, symbol or atomic number to jump to an element and highlight it. You can also color the whole table by electronegativity, atomic radius, ionization energy, density or melting point instead of by category, which makes the periodic trends visible at a glance. The selected element and coloring are kept in the page link, so you can share exactly what you are looking at.

Elements are arranged in order of atomic number, the number of protons in the nucleus. Each row, or period, starts a new electron shell, and each column, or group, holds elements with the same arrangement of outer electrons, which is why they behave alike. Groups 1 and 2 form the s-block, groups 13 to 18 the p-block, and the transition metals in groups 3 to 12 the d-block. The lanthanides and actinides, the f-block, are usually drawn below the main table to keep it a manageable width; they belong between groups 2 and 3 in periods 6 and 7.

Atoms get smaller from left to right across a period, because added protons pull the same shell in tighter, and larger down a group as new shells are added. Ionization energy and electronegativity follow the opposite pattern: they rise toward the top right. Fluorine is the most electronegative element at 3.98 on the Pauling scale, while cesium is among the least at 0.79. Helium has the highest first ionization energy, 24.587 eV.

Physical properties show broader patterns. Of the elements, 14 are gases at room temperature and only Bromine and Mercury are liquids. Osmium is the densest, about 22.59 g/cm³, and tungsten has the highest melting point of any metal at 3422 °C.

Atomic weights are the IUPAC CIAAW 2021 standard values in abridged form, the same ones used by this site's molar mass and stoichiometry calculators; for elements with no stable isotopes, the mass number of the longest-lived isotope is shown. Electronegativities, radii, ionization energies, densities and transition temperatures come from the CRC Handbook of Chemistry and Physics and NIST data. Gas densities are given at 0 °C and 1 atm. For the heaviest elements, many properties have never been measured and are left blank rather than estimated.

Dmitri Mendeleev published the first widely recognized periodic table in 1869, arranging the 63 elements then known by atomic weight and grouping those with similar chemistry. He left gaps for elements he predicted but had not seen, and the later discovery of gallium, scandium and germanium with properties close to his forecasts made the table famous. In 1913 Henry Moseley showed from X-ray spectra that atomic number, not weight, sets the order, which explained why a few pairs such as tellurium and iodine seemed out of place. Quantum mechanics later explained the shape of the table through electron shells and subshells.