Periodic table of the elements
All 118 elements, with the official IUPAC name and symbol and the standard atomic weight published by CIAAW. Select any box to see the full record.
Updated on October 7, 2026
The table
The table is laid out the usual way: 18 columns, 7 rows, and the f-block (lanthanides and actinides) pulled out underneath so the grid stays readable. Colour marks the chemical family; the search box filters by name, symbol or atomic number.
- Alkali metal
- Alkaline earth metal
- Transition metal
- Post-transition metal
- Metalloid
- Reactive nonmetal
- Halogen
- Noble gas
- Lanthanide
- Actinide
Source: CRC Handbook of Chemistry and Physics — raio atômico covalente e eletronegatividade de Pauling (tabelas de referência clássicas)
How to read an atomic weight honestly
An atomic weight is not a single clean number for every element. For most, IUPAC publishes a value plus a standard uncertainty, shown here in brackets after the last digits. For fourteen elements — hydrogen, lithium, boron, carbon, nitrogen, oxygen, magnesium, silicon, sulfur, chlorine, argon, bromine, thallium and lead — IUPAC publishes a range instead, because the mixture of isotopes genuinely differs from one sample to another. For those we show the conventional atomic weight and say so on the element record.
Elements with no stable nuclide, such as technetium, promethium and everything from polonium upwards except thorium, protactinium and uranium, get no standard atomic weight at all. For them the number in brackets is the mass number of the longest-lived isotope, which is a different kind of statement. Any page that prints one number and hides this distinction is simplifying.
Groups, periods and blocks
The group is the column and tells you how many electrons sit in the outer shell, which is why group 1 metals all react with water and group 18 gases react with almost nothing. The period is the row, that is the outermost occupied shell. The block (s, p, d, f) says which type of orbital is being filled.
We leave the group empty for the 15 lanthanides and the 15 actinides. Group 3 is the one place where tables genuinely disagree: IUPAC has a provisional recommendation putting lutetium and lawrencium there, while many printed tables use lanthanum and actinium. Rather than pick a side silently, we show no group for the whole f-block.
How to read this page
How to read the numbers here
Every value on "Periodic table of the elements" comes from the source named beside its section, never from an estimate of our own with no origin.
Where the data comes from
Each section of "Periodic table of the elements" names its official source; the verification date sits at the top of the page.
What the number doesn’t tell you
Atomic weight, molar mass and standard uncertainty are measurement concepts: none of them say anything about a real sample’s purity, physical state or specific isotope.
More about “Periodic table of the elements”
How many elements sit in each block
Of the 118 elements on this table, 14 sit in the s block, 36 in the p block, 38 in the d block (the transition metals) and 30 in the f block (lanthanides and actinides). The d block alone is bigger than the s and f blocks combined.
14 elements have their atomic weight published as a range and 34 have no stable nuclide — add the two groups together, and more than a quarter of the table you’re looking at in "Periodic table of the elements" has no "clean" atomic weight in the sense of a single exact measurement.
Words on this page
Atomic number
The number of protons in an atom’s nucleus, written Z. It is this number, not the mass, that defines which element an atom is: every atom with 8 protons is oxygen, whether it has 8 or 18 neutrons.
Standard definition by IUPAC · Atomic number
Atomic weight
The average weight of an element’s atoms, weighted by how abundant each isotope is in nature, in atomic mass units. For 14 elements CIAAW publishes a range instead of a single value, because that abundance varies a little from sample to sample.
Standard definition by CIAAW — Commission on Isotopic Abundances and Atomic Weights · Atomic weight
Isotope
Atoms of the same element (same number of protons) with a different number of neutrons, and therefore a different mass. Carbon-12 and carbon-14 are isotopes of carbon; only the second one is radioactive.
Group and period
The group is the periodic table’s column and shows how many electrons sit in the outer shell; the period is the row and shows how many shells the atom has. Elements in the same group tend to react in similar ways.
Standard definition by IUPAC · Group and period
s/p/d/f block
A split of the periodic table by the type of orbital receiving the atom’s last electron. Alkali and alkaline-earth metals sit in the s block, most everyday elements in the p block, transition metals in the d block, and lanthanides and actinides in the f block.
Standard definition by IUPAC · s/p/d/f block