Periodic table
Tap an element to watch its atom build itself. Heat the table, play its history, or color it by trends and charges.
- Atomic mass
- 12.011
- Per shell
- 2, 4
- Valence electrons
- 4
- Protons · neutrons
- 6 · 6
- Configuration
- [He] 2s² 2p²
How to read the periodic table
Every tile shows one element. The small number is its atomic number, the count of protons in its nucleus. The letters are its symbol. Elements run in order of atomic number, left to right and top to bottom.
The 7 rows are periods: each one adds a new electron shell, which is why atoms grow down the table. The 18 columns are groups: elements in a group share the same number of valence electrons, so they react in similar ways. Sodium and potassium both fizz in water; neon and argon both ignore almost everything.
Two patterns explain most of chemistry. Moving right, atoms hold their electrons tighter (higher electronegativity and ionization energy). Moving down, atoms get bigger and their outer electrons get easier to remove.
Explore with animations
- Electron configuration explorer: add electrons one at a time and watch the orbitals fill.
- Periodic trends: see electronegativity, atomic radius and ionization energy rise and fall.
- Periodic table with charges: the ion each element usually forms.
- Groups and families: alkali metals to noble gases.
- Printable periodic table: a clean copy for class.
Periodic table questions
How many elements are on the periodic table?
118. The last four, nihonium (113), moscovium (115), tennessine (117) and oganesson (118), were named in 2016. Oganesson is the heaviest element made so far.
How is the periodic table arranged?
Elements are placed in order of atomic number, the number of protons in the nucleus. Rows are called periods; columns are groups. Elements in the same group have the same number of valence electrons, so they behave alike.
What do the colors mean?
Each color is a family of elements: alkali metals, alkaline earth metals, transition metals, post-transition metals, metalloids, nonmetals, halogens, noble gases, lanthanides and actinides. Switch to Trends, State or Charges to color the table by other properties.
Why are two rows separated at the bottom?
The lanthanides (57–71) and actinides (89–103) belong in periods 6 and 7. Pulling them out keeps the table narrow enough to read.
Who made the periodic table?
Dmitri Mendeleev published the first widely used periodic table in 1869. He left gaps for elements no one had found yet and predicted their properties, and gallium, scandium and germanium later filled them.