Periodic table of the elements
Tap any element to see its atomic number, standard atomic weight, group, period, block and category. Search by name, symbol or number, and switch between the classic table and a plain list that is easier on a small screen.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Look at the table or switch to List. Colours show the category; the key is under the table.
- Type in the search box to find an element by name, symbol (He) or atomic number (2). In the table, elements that do not match fade out.
- Tap an element to see its details under the table.
What the details mean
- Atomic number: the number of protons, which defines the element.
- Atomic weight: the average atomic mass, as a conventional rounded value.
- Group and period: the column (1 to 18) and the row (1 to 7).
- Block: s for groups 1 and 2 and helium, p for groups 13 to 18, d for groups 3 to 12, and f for the two lower rows. Lutetium and lawrencium are sometimes placed in the d block.
- Category: a common grouping by properties. Elements 109 to 118 have been made only a few atoms at a time, so their chemistry is not established and they are left unclassified.
Worked example
Search for Fe. Iron is element 26 with a weight of 55.845, in group 8, period 4, d block, a transition metal.
Tips
- Atomic weights here are for study and quick reference. For exact work, use the current IUPAC table.
- Some charts classify a few elements differently, for example polonium or astatine. Categories are a convention.
Frequently asked questions
How many elements are there?
There are 118 confirmed elements, from hydrogen (1) to oganesson (118). The last four, nihonium, moscovium, tennessine and oganesson, were named in 2016.
What is atomic weight?
It is the average mass of an element's atoms as found in nature, in atomic mass units, so it is not a whole number for most elements. For elements with no stable isotope, the table shows the mass number of the longest-lived isotope in square brackets.
What do group, period and block mean?
A group is a column (1 to 18) of elements with similar behaviour. A period is a row (1 to 7). The block (s, p, d or f) names the kind of orbital that is being filled across the table.
Why are the lanthanides and actinides below the table?
They are 15 elements each that would make the table very wide, so they are shown in two separate rows. This table gives them no group number because textbooks disagree on which elements belong in group 3.
Why does the table say aluminium and caesium?
Those are the IUPAC spellings. Searching for the US spellings aluminum and cesium also finds them.