Tap an element to open its card and 3D atom. Tap a family in the key to highlight it. On a phone, swipe the table sideways.
Add and remove protons, neutrons and electrons. The protons decide the element, protons + neutrons give the mass number, and protons − electrons give the charge. Can you make a stable isotope, a radioactive one and an ion? (Up to calcium, element 20.)
Plot a property against atomic number and the pattern repeats in every period, which is why the table is called periodic. Highlight a group or a period, then tap a point to open that element.
Elements in the same group react in the same way, just faster or slower. Drop alkali metals into water, mix halogens with salt solutions, and hold metal compounds in a Bunsen flame.
| Halogen | At room temperature | Colour | Reactivity |
|---|---|---|---|
| Fluorine, F₂ | gas | pale yellow | most reactive |
| Chlorine, Cl₂ | gas | yellow-green | ↓ less reactive down the group |
| Bromine, Br₂ | liquid | red-brown (orange vapour) | |
| Iodine, I₂ | solid | grey-black (purple vapour) |
Safety: chlorine and bromine are toxic and rubidium and caesium are far too dangerous for school labs. These animations show what happens; do not try them without a teacher.
Atoms lose or gain electrons until their shells are full like a noble gas. Metals lose electrons and become positive ions; non-metals gain electrons and become negative ions. Then the charges have to cancel out in a compound.
Advanced level adds transition-metal ions such as Fe²⁺ and Fe³⁺, and groups of atoms with a charge (hydroxide, nitrate, sulfate, carbonate, ammonium).
Slide through the years and watch the table fill in. Only about a dozen elements were known in ancient times; most were found between 1750 and 1900, and the heaviest were made in laboratories.
In 1871 Mendeleev described three missing elements in detail: eka-boron, eka-aluminium and eka-silicon (“eka” means “one beyond”). When scandium (1879), gallium (1875) and germanium (1886) were found, they matched his predictions closely, and chemists accepted his table. Here are two of them (X = the missing element):
| Property | Eka-aluminium (predicted 1871) | Gallium (found 1875) | Eka-silicon (predicted 1871) | Germanium (found 1886) |
|---|---|---|---|---|
| Relative atomic mass | about 68 | 69.7 | about 72 | 72.6 |
| Density | 5.9 g/cm³ | 5.9 g/cm³ | 5.5 g/cm³ | 5.3 g/cm³ |
| Melting point | low | 30 °C | high | 938 °C |
| Oxide | X₂O₃ | Ga₂O₃ | XO₂, density 4.7 g/cm³ | GeO₂, density 4.2 g/cm³ |
| Chloride | XCl₃ | GaCl₃ | XCl₄, boils below 100 °C | GeCl₄, boils at 86 °C |
Mendeleev also swapped tellurium and iodine so that iodine sat with the other halogens, even though tellurium is heavier. Moseley’s work in 1913 showed why he was right: the order is by atomic number, not mass.
Ten rounds. Read the clue, then tap the right element on the table as fast as you can. The squares are all one colour, so you have to know where the families are. Basic clues use names, symbols, groups and periods; Advanced clues use electron configurations and trends.
A blank periodic table to label, the kind you meet in tests. Pick Basic (9 labels) or Advanced (13). Switch between the labeled table, a blank one, a label quiz and match the jobs, where you pair each label with its description. On a phone, swipe the diagram sideways.
Tap a word, then tap the numbered box it belongs to (on the diagram or in the list below). Tap a filled box to take the word back.
Each line describes the job of one part. Tap a part name, then tap the box next to the job it does. Tap a filled box to take the word back.
A printable worksheet: label a blank periodic table, fill in protons, neutrons and electrons, draw electron shells, multiple choice and explain-the-trend questions, with an answer key. Also a full-colour periodic table and a blank one to print on A4 (landscape), or save as PDF.
An element is a substance made of only one kind of atom. Every atom has a tiny nucleus of protons (+) and neutrons (no charge), with electrons (−) around it. The number of protons, the atomic number, decides which element it is: 6 protons is always carbon, 26 is always iron. A neutral atom has as many electrons as protons.
Each square shows the atomic number, the chemical symbol (one or two letters, the first a capital), the name and the relative atomic mass, the average mass of its atoms compared with 1/12 of a carbon-12 atom. Protons = atomic number; neutrons in an atom = mass number − atomic number (for chlorine-35: 35 − 17 = 18).
Electrons fill shells: 2 in the first, then 8, 8 for the first 20 elements. The period number tells you how many shells are in use, and for the main groups the last digit of the group number tells you the outer electrons (sodium: period 3, group 1, shells 2, 8, 1). Atoms react to gain, lose or share outer electrons, so a group shares its chemistry: group 1 metals all fizz in water, group 17 halogens all form salts, group 18 noble gases hardly react at all.
Going down a group, atoms get bigger because there are more shells, so the outer electron is held more weakly: alkali metals get more reactive, and halogens get less reactive. Going across a period, protons are added while the shell stays the same, so atoms get smaller and hold their electrons more tightly: ionisation energy and electronegativity rise. Metals are on the left, non-metals on the right, with the metalloids along the staircase between them.
Open sodium and chlorine and compare their shells. Slide the temperature to 30 °C and watch gallium and caesium melt. Colour the table by atomic radius, then look at the Periodic Trends chart: the radius jumps up at each group 1 metal and shrinks across each period.
| Part | What it tells you | Example |
|---|---|---|
| Atomic number | Number of protons (and electrons in a neutral atom); the order of the table | Na = 11 |
| Relative atomic mass | Average mass of the atoms, counting all isotopes; round it to get the mass number of the most common isotope (not always exact) | Cl = 35.45 |
| Group (column 1–18) | Same outer electrons, similar reactions | Group 1: Li, Na, K… |
| Period (row 1–7) | Number of electron shells in use | Period 3: 3 shells |
| Metals / non-metals | Metals (about three-quarters of all elements) are on the left and centre; non-metals on the right; metalloids along the staircase | Si is a metalloid |
| Blocks s, p, d, f | Which type of orbital the last electron goes into (Advanced) | Fe is d-block |
Element data come from the PubChem Periodic Table (U.S. National Library of Medicine), with IUPAC abridged standard atomic weights. For elements with no stable isotope the mass number of a long-lived or reference isotope is shown in brackets, for example [222] for radon. Atomic radius here is the calculated radius (Clementi, Raimondi & Reinhardt, 1967, available up to radon); measured covalent or metallic radii give different numbers but the same trends. Polonium is shown as a metalloid, as in PubChem; many school tables call it a metal. Where lanthanum, actinium, lutetium and lawrencium belong is still debated; this table puts all of 57–71 and 89–103 in the two bottom rows. Melting and boiling points are at normal pressure; values for the heaviest elements are predicted or unknown, and the categories of elements beyond 103 are predictions because only a few atoms have ever been made. Neutron numbers are for the most common isotope (or the reference isotope for radioactive elements).
Formulas: neutrons = mass number − atomic number · electrons (neutral atom) = protons · shells for the first 20 elements fill 2, 8, 8, 2.
References: PubChem Periodic Table, pubchem.ncbi.nlm.nih.gov/periodic-table; Clementi, Raimondi & Reinhardt (1967), Journal of Chemical Physics 47:1300; IUPAC Commission on Isotopic Abundances and Atomic Weights, standard atomic weights (2021); Atkins & Jones, Chemical Principles; Royal Society of Chemistry, Periodic Table.
There are 118 confirmed elements. About 90 occur naturally on Earth; the rest have been made in laboratories and reactors. The newest four (nihonium, moscovium, tennessine and oganesson) were named in 2016.
Key takeaway: Element 118, oganesson, is the heaviest made so far.Protons = atomic number. In a neutral atom, electrons = protons. Neutrons = mass number − atomic number; for a quick estimate round the relative atomic mass (carbon: 12 − 6 = 6 neutrons). The card above shows the most common isotope.
Key takeaway: Atomic number gives protons and electrons; mass number minus atomic number gives neutrons.A group is a column (1–18): its elements have the same number of outer electrons and react in similar ways. A period is a row (1–7): its elements have the same number of electron shells.
Key takeaway: Groups go down, periods go across.Hydrogen has one outer electron like the alkali metals, so it is placed above group 1, but it is a gas and a non-metal. Some tables float it above the middle because it also behaves a little like the halogens (it can gain an electron).
Key takeaway: Hydrogen is a special case: one electron, but a non-metal.Only two: bromine (a non-metal) and mercury (a metal). Gallium and caesium melt just above room temperature (about 30 °C and 28 °C), so they melt on a hot day or in your hand. Try the temperature slider.
Key takeaway: Bromine and mercury are the only liquid elements at 20 °C.Dmitri Mendeleev published his table in 1869. He left gaps for elements nobody had found yet and predicted their properties; gallium (1875), scandium (1879) and germanium (1886) fitted his predictions. Today the table is ordered by atomic number, an idea that came from Henry Moseley in 1913.
Key takeaway: Mendeleev’s gaps and predictions made the table famous.They belong in periods 6 and 7 between groups 2 and 4, but writing them in place would make the table 32 columns wide, so they are printed as two separate rows. They are the f-block, where electrons fill f orbitals.
Key takeaway: The two bottom rows are cut out of periods 6 and 7 to save space.Across a period each element has one more proton but its outer electrons are in the same shell. The bigger nuclear charge pulls the shells in more tightly, and the inner electrons do not shield much more. Down a group a new shell is added each time, so atoms get bigger.
Key takeaway: More protons, same shell: smaller atoms.Their outer shell is full (2 electrons for helium, 8 for the others), so they have no tendency to gain, lose or share electrons. Under special conditions xenon and krypton do form a few compounds.
Key takeaway: A full outer shell makes an atom stable.For potassium and calcium the 4s orbital is lower in energy than 3d, so it fills first. For chromium ([Ar]3d54s1) and copper ([Ar]3d104s1) a half-full or full d subshell gives a lower total energy, so one 4s electron moves into 3d. When transition metals form ions they lose 4s electrons first.
Key takeaway: Electron energies change as the nuclear charge grows; Cr and Cu are the famous exceptions.