Rows are periods
The seven rows each stand for one electron shell being filled. Move along a row and atoms get smaller and hold their electrons more tightly, because the growing nuclear charge pulls the same shell in closer.
Chemistry reference
All 118 elements with atomic mass, electron configuration, melting points and more. Click a square for the full page, or colour the whole table by any property.
118
elements, free to use
Point at any square for a quick look, or click through for the full page.
All 118
The coloured line on top of each square marks its family. Pick a scheme above to fill the squares in.
The ten families chemists group the elements into, plus a slot for the handful of superheavy elements whose chemistry is still an open question.
Blocks name the outermost orbital an element fills, which is why the shape of the table follows them so closely.
Measured at 25 degrees Celsius. Only bromine and mercury are liquid, and eleven elements are gases. For the heaviest synthetic ones the state is a prediction, since too few atoms have ever existed to look at.
Everything from polonium upward is radioactive, and so are the two gaps lower down the table at technetium and promethium.
Hatched squares have no published measurement, so they are left blank rather than set to zero.
How it works
The seven rows each stand for one electron shell being filled. Move along a row and atoms get smaller and hold their electrons more tightly, because the growing nuclear charge pulls the same shell in closer.
The eighteen columns gather elements with the same number of outer electrons, which is why sodium and potassium both fizz in water and why the noble gases in the last column mostly refuse to react with anything.
The s, p, d and f labels say which type of orbital the outermost electrons sit in. That is the reason for the table's odd shape, including the two rows of lanthanides and actinides usually printed underneath.
118
confirmed elements, from hydrogen to oganesson
94
of them occur naturally somewhere on Earth
2
are liquid at room temperature: bromine and mercury
1869
the year Mendeleev published his version of the table
Browse
Every element has its own page with the full set of measured properties, a shell diagram, and bars showing where it sits against the other 117.
Questions
The periodic table is a chart of all the known chemical elements, arranged in order of atomic number, which is the number of protons in one atom of that element. Reading left to right and top to bottom takes you from hydrogen at number 1 through to oganesson at number 118. Elements in the same vertical column behave in similar ways because they have the same number of electrons in their outer shell.
There are 118 confirmed elements. Ninety-four of them occur naturally on Earth, at least in trace amounts, and the remaining twenty-four have only ever been made in particle accelerators. The last four to be named were nihonium, moscovium, tennessine and oganesson, all added in 2016.
Dmitri Mendeleev published the version the modern table grew out of in 1869. Several chemists had spotted the repeating pattern before him, but Mendeleev was the one who left gaps for elements nobody had found yet and predicted their properties. Gallium, scandium and germanium turned up later and matched his predictions closely, which is what convinced everyone else.
The seven horizontal rows are called periods, and each one corresponds to an electron shell being filled. The eighteen vertical columns are called groups, and elements sharing a group share a valence electron count, so they react in similar ways. Group 1 holds the reactive alkali metals, group 17 the halogens, and group 18 the noble gases that barely react at all.
Atomic number counts the protons in the nucleus and never changes for a given element. Atomic mass is the average weight of that element’s atoms, measured in unified atomic mass units, and it accounts for the mix of isotopes found in nature. Carbon has atomic number 6 and atomic mass 12.011, because most carbon is carbon-12 but a small fraction is heavier.
Yes. Every element page, every trend chart and every game on this site is free, with no account, no sign up, no trial and no subscription. Nothing is held back behind a paywall and you do not need to give an email address to use any of it.
It does. The table scrolls sideways on a narrow screen so the squares stay big enough to tap, and every element page is built to read comfortably on a phone. There is no app to install.
Please do. The site is free for students and teachers, works on a school network without a login, and each element page lists the data it uses so a value can be checked against its source. Printing a page from the browser gives a clean copy without the navigation.
Practise
Three free games for learning the periodic table properly. Nothing to sign up for, and your scores stay on your own device.
Daily
Wordle, with an element as the answer. Six guesses, and every wrong one narrows the group, period, block and atomic number until only one is left.
PlayTimed
Sixty seconds of symbols and names. The quickest way to find out which ones you actually know.
PlaySpatial
Given a name, click its square on a blank table. The layout is the part exams test, so it is the part worth drilling.
Play