Explore 118 elements, compare properties, and visualize trends and states with a simplified 1 atm model
Mendeleev (1869) arranged the elements mainly by atomic mass and noticed that properties recurred — so clearly that he left gapsand predicted the properties of elements not yet discovered (his "eka-silicon" turned out to be germanium). Moseley (1913) used X-ray spectra to establish that the correct ordering criterion is the atomic number , the number of protons; nuclear charge is . This is the basis of the modern periodic law:
In chemistry, "periodic" means that as you move through certain configurations and properties recur. It is not a mathematical periodic function with a fixed interval: the periods contain 2, 8, 8, 18, 18, 32 and 32 elements. Each main row represents one period, with the f block detached for convenience.
The recurrence has an electronic cause. Each period begins when a new principal level starts to fill, although and subshells may also fill along the way. Among representative elements, a group shares a valence pattern and therefore similar chemistry: alkali metals end in and tend to lose one electron; halogens end in; and noble gases have closed shells, although the heavier ones can form compounds.
The s, p, d and f blocks identify the subshell receiving the differentiating electron. The f block is the reason for the two detached rows at the bottom: drawn in their true place, lanthanides and actinides would stretch the table to 32 columns. That is what the 57–71 and 89–103 markers in column 3 are for — click them to highlight how those series fit into the long form. The exact assignment of group 3 varies among published tables.
Almost every trend follows from a single idea: the effective nuclear charge , the charge an outer electron actually "feels" after the inner electrons screen the nucleus. Moving right across a period adds protons while the shell stays the same, so grows; moving down adds a whole new shell, leaving the outer electron farther away and better screened.
You can seethis trend in the calculator: switch "Color by → Electronegativity" and the diagonal gradient toward fluorine appears on its own. Mind the exceptions: full and half-full subshells add extra stability. Noble gases are not treated uniformly across compilations either: He, Ne and Ar have no in this dataset, while Kr, Xe and Rn have tabulated values.
When a standard atomic weight exists, the tabulated value is the weighted average of isotopes in terrestrial materials by abundance :
That is why chlorine "weighs" 35.45 u: it is ~76% and ~24% , not an isotope of mass 35.45. And when you see a mass in brackets — [97] for Tc, [223] for Fr or [294] for Og — the element has no standard atomic weight. Following IUPAC, the table shows the mass number of the nuclide with the longest confirmed half-life; this does not simply depend on whether the element occurs naturally in trace amounts.
At 25 °C and 1 atm only two elements are liquid: Hg and Br. But gallium melts at 29.8 °C and cesium at 28.4 °C. The "Physical state at T" mode uses a simplified 1 atm model, not a complete phase diagram:
At an exact transition point, phases coexist; by convention the visualization shows the higher-temperature phase. Two exceptions are explicit: helium does not solidify by cooling at 1 atm, and arsenic sublimes near 614 °C. Its 817 °C value is the triple point at about 28 atm, so it is not used as an atmospheric-pressure melting point. The model also omits plasma, ionization and allotrope transitions.
?element=Fe&vs=Cu.Read the colors carefully
Density is colored by quantiles: each color band holds an equal share of elements. With 5 orders of magnitude between gaseous H and osmium, a linear or logarithmic scale would leave almost every solid the same blue. Gas densities are converted from values at standard conditions, while solids and liquids may use other reference conditions: the map compares ranges rather than measurements at one common temperature. Gray means data are missing; ≈ marks predictions for superheavy elements. The phase model assumes 1 atm and omits other pressures, supercritical regions and plasma.
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The atomic masses in this table are the ones Advanced Stoichiometry uses to compute molar masses and balance equations. The oxidation states on each card are the starting point of Redox Balancing by Half-Reactions. And electronegativity anticipates the bond type you will meet in those compounds.