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Periodic table (names, atomic mass, electron configuration)

Browse all 118 elements: name, atomic mass, metal / metalloid / nonmetal class, group and period, electron configuration, melting and boiling points. Click an element for its electron configuration and shell diagram.

Atomic masses are abridged IUPAC standard values; a value in parentheses is the mass number of the longest-lived isotope, used when an element has no stable isotope. Electronegativity is on the Pauling scale; melting and boiling points are at 1 atm, left blank where uncertain or where pressure is needed. Most properties of elements above 103 are predicted, as only a few atoms have ever been made.

FAQ

Is a metalloid a metal or a nonmetal?
Something in between. Boron, silicon, germanium, arsenic, antimony and tellurium are the usual ones, and they are widely used in semiconductors. Sources draw the line slightly differently; this tool uses those six.
What does a notation like [Ar] mean in an electron configuration?
It stands for the electron configuration of that noble gas (argon here), written in place of the inner shells. The detail view also shows the full, unabbreviated configuration.
Why do chromium and copper break the filling rule?
A half-filled or completely filled d subshell is slightly more stable. Chromium (3d⁵ 4s¹) and copper (3d¹⁰ 4s¹) are the classic cases; a few other transition metals, lanthanides and actinides are exceptions too, and the detail view marks them.
What do the parentheses around an atomic mass mean?
The element has no stable isotope, so no standard atomic weight exists. The mass number of its longest-lived isotope is shown instead.
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