About Periodic Table
The periodic table arranges the chemical elements by atomic number, the count of protons in the nucleus, so that elements with similar properties fall in the same column. This table lists all 118 known elements with symbol, name, atomic mass, period (row), group (column, 1 to 18), and electron block. Atomic masses are abridged standard atomic weights. A value in square brackets is the mass number of a long-lived isotope of an element that has no stable form.
How to use Periodic Table
- Fill in "Search by name, symbol, or atomic number" and "Block".
- The result appears below and updates as you type.
- Copy the result with the copy button, or download it as a file where that is offered.
Questions about Periodic Table
Why do some elements show a mass in brackets?
Those elements have no stable isotopes, so no standard atomic weight can be defined from natural samples. The bracketed number is the mass number of one of the longest-lived known isotopes, and sources differ for the heaviest elements.
Why do lanthanides and actinides have no group number?
The 15 lanthanides and 15 actinides fill the f electron subshell and are usually drawn in two separate rows below the main table. They are not assigned to the 18 numbered groups, so this table labels them as f-block.
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