Periodic Table
Click any element to see its atomic number and mass, electron configuration, electronegativity, group, period and state. Search by name or symbol, filter by type, and work out molar masses.
Molar mass calculator
Examples:
| Element | Atoms | Atomic mass | Total mass | Mass % |
|---|
How to use the periodic table
- Click or tap any element to see its details below the table: atomic mass, electron configuration, electronegativity, group, period, block and state at room temperature.
- Type a name, symbol or atomic number in the search box to jump to an element, or pick a family such as halogens from the menu (or click a color in the key) to highlight it.
- To find a molar mass, type a formula such as Ca(OH)2 or CuSO4·5H2O. The total and the share of each element appear instantly.
How the periodic table is organized
Elements are listed in order of atomic number, the number of protons in the nucleus. Each row is a period: elements in the same period have the same number of electron shells. Each column is a group: elements in a group have the same number of outer (valence) electrons, so they behave similarly. That is why sodium and potassium, both in group 1, react the same violent way with water.
The two rows below the main table, the lanthanides and actinides, belong in periods 6 and 7. They are shown separately so the table fits on a page. Colors show each element’s family, from reactive alkali metals on the left to unreactive noble gases on the right, with metalloids forming a staircase between the metals and nonmetals.
Reading the details
Atomic mass is the average mass of an element’s atoms in atomic mass units (u), weighted by how common each isotope is in nature. Values in brackets, such as [98] for technetium, are the mass number of the longest-lived isotope, for elements with no stable form. Electron configuration shows how electrons fill the shells, written after the previous noble gas; a few elements such as chromium and copper are exceptions to the usual filling order. Electronegativity (Pauling scale) measures how strongly an atom pulls shared electrons, from 0.79 for caesium to 3.98 for fluorine.
Working out molar mass
Molar mass is the mass of one mole of a substance in grams. Add up the atomic masses of every atom in the formula: water, H₂O, is 2 × 1.008 + 15.999 = 18.015 g/mol. For brackets, multiply everything inside by the number after them, so Ca(OH)₂ has two oxygen and two hydrogen atoms. In a hydrate such as CuSO₄·5H₂O, the 5 multiplies the whole water molecule.
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Frequently asked questions
Where do the atomic masses come from?
They are the standard atomic weights published by IUPAC, rounded to a practical number of decimal places, which is what most textbooks use.
How many elements are there?
118 elements are confirmed, from hydrogen (1) to oganesson (118). Elements beyond 94 do not occur naturally in any meaningful amount and are made in laboratories.
Why are some element properties marked predicted or unknown?
The heaviest elements have only been made a few atoms at a time and last fractions of a second, so their chemistry is based on theory rather than measurement.
Can the molar mass calculator handle brackets and hydrates?
Yes. Use round, square or curly brackets, and a dot, asterisk or · for hydrates, for example [Cu(NH3)4]SO4 or MgSO4*7H2O. Symbols are case-sensitive: Co is cobalt, CO is carbon monoxide.
Is anything sent to a server?
No. Everything is calculated in your browser, and nothing you enter leaves your device.