🎮 How to Use
- Click any element to see its name, atomic number, mass, and category.
- Color-coded by group: alkali metals, halogens, noble gases, etc.
About this tool
118 known chemical elements. Organized by atomic number (proton count). Rows = periods (electron shells). Columns = groups (similar properties). Color groups: alkali metals, alkaline earth, transition metals, lanthanides, actinides, post-transition, metalloids, nonmetals, halogens, noble gases.
What the periodic table is
The periodic table is a chart that arranges all 118 known chemical elements by increasing atomic number so that elements with similar properties line up in columns. It is the single most useful map in chemistry: an element's position tells you, at a glance, how it is likely to react, what charge its ions tend to take, and which other elements it resembles.
This interactive version lets you explore each element and its group. The genius of the layout, first published by Dmitri Mendeleev in 1869, is that it turns a long list of substances into a grid whose shape encodes the rules of chemical behaviour.
The name comes from periodicity: chemical properties repeat at regular intervals as atomic number rises, which is why each new row begins a fresh cycle from a reactive metal on the left to an inert noble gas on the right. Mendeleev trusted this pattern so completely that he left gaps for elements not yet discovered, such as gallium and germanium, and correctly predicted their properties years before anyone found them. That is the lasting power of the table: it is not just a catalogue but a working model that lets chemists anticipate how an element will behave from its place in the grid alone.
How the layout encodes structure
Two coordinates place every element, and each carries chemical meaning.
Atomic number Z = number of protons (also electrons if neutral) Period (row) = highest occupied electron shell (1 to 7) Group (column) = number of valence (outer-shell) electrons Reading order = left to right, top to bottom, by rising Z
Moving left to right across a period adds one proton and one electron at a time, so elements shift gradually from reactive metals, through metalloids, to non-metals and finally a noble gas. Moving down a group keeps the valence count the same, which is why a column shares a family resemblance.
Worked example: reading sodium
Take sodium, symbol Na, at atomic number 11.
- Atomic number 11: the nucleus has 11 protons, and a neutral atom has 11 electrons.
- Electron shells: 2 in the first, 8 in the second, 1 in the third, so sodium sits in period 3.
- Valence electrons: just 1 in the outer shell, placing it in group 1.
- Group 1 means alkali metal: it gives up that single electron easily, forming a 1+ ion.
- Predicted behaviour: soft, very reactive, reacts vigorously with water, and pairs with group 17 elements like chlorine to make salts (NaCl).
The main element families
Elements are coloured by family, each defined by shared outer-electron structure and behaviour.
| Family | Group(s) | Characteristic |
|---|---|---|
| Alkali metals | 1 | Soft, very reactive, form 1+ ions |
| Alkaline earth metals | 2 | Reactive, form 2+ ions |
| Transition metals | 3 to 12 | Hard, dense, multiple oxidation states |
| Metalloids | along the metal/non-metal line | Semiconducting, mixed properties |
| Halogens | 17 | Very reactive non-metals, form 1- ions |
| Noble gases | 18 | Full outer shell, almost inert |
| Lanthanides / actinides | f-block | Rare earths and radioactive metals |
Common pitfalls
- Confusing atomic number with atomic mass. The atomic number is the proton count and is always a whole number; atomic mass is roughly protons plus neutrons and is usually a decimal average over isotopes.
- Assuming group numbers run 1 to 8. The modern convention numbers groups 1 to 18 across the full table, including the transition metals.
- Placing hydrogen with a fixed family. Hydrogen has one electron like group 1 but behaves uniquely and is often shown apart; it is not a typical alkali metal.
- Reading periods and groups the wrong way. Periods are horizontal rows, groups are vertical columns. Properties trend gradually across a period and repeat down a group.
- Thinking all elements are natural. Elements above 94 are synthetic and many exist only for moments before decaying.
- Ignoring the lanthanides and actinides. The two detached rows belong inside the table; they are pulled out only to keep the chart a sensible width.
Related tools
Frequently asked questions
How is the periodic table organised?
Elements are arranged by increasing atomic number, which is the number of protons. Rows are called periods and correspond to electron shells, while columns are called groups and contain elements with similar chemical behaviour because they share the same number of outer-shell electrons.
What is the difference between a period and a group?
A period is a horizontal row; moving across it, atomic number rises one at a time and properties shift gradually. A group is a vertical column; elements within it react in similar ways, such as the highly reactive alkali metals in group 1 or the inert noble gases in group 18.
What does the atomic number tell me?
The atomic number equals the number of protons in the nucleus, and in a neutral atom it also equals the number of electrons. It uniquely identifies the element and sets its position in the table. Hydrogen is 1, carbon is 6, and oxygen is 8.
Why do elements in the same group behave alike?
Because chemical reactions are driven by the outermost electrons, and elements in a group all have the same number of them. Group 1 metals each have one outer electron they readily give up, while group 17 halogens each need just one more electron, which is why both groups are so reactive.
How many elements are there?
There are 118 confirmed elements, numbered 1 (hydrogen) through 118 (oganesson). The first 94 occur naturally on Earth in at least trace amounts, and elements 95 and above are synthetic, created in particle accelerators and often existing only for fractions of a second.