Periodic table of elements

118 elements · point, tap, or tab to an element for details

Runs entirely in your browser; nothing is uploaded or stored. On a small screen, scroll the table sideways. Hazard notes are rough orientation only: toxicity depends on the chemical form, dose, route, and exposure—not just the element name.

6 C 12.011
2 4
atomic number symbol atomic mass (u) electrons per shell (top = inner)
Lanthanides — period 6, groups 3 (elements 57–71)
Actinides — period 7, groups 3 (elements 89–103)
Atomic number
Atomic mass
Group
Period
State (25°C)
Electron shells
Valence electrons
Electronegativity
Toxicity

Element groups

Alkali metals
Alkaline earth metals
Transition metals
Post-transition metals
Metalloids
Reactive nonmetals
Halogens
Noble gases
Lanthanides
Actinides

Key formulas & constants

Avogadro's number (Nₐ)6.022 × 10²³ mol⁻¹
Molar massM = m / n
Ideal gas lawPV = nRT
Gas constant (R)8.314 J mol⁻¹ K⁻¹
Molarityc = n / V
pH definitionpH = −log[H⁺]
pH + pOH at 25°C= 14
Moles ↔ massn = m / M
Atomic mass unit (u)1.661 × 10⁻²⁷ kg
Max electronegativityF = 3.98 (Pauling)
Periodic trends
Atomic radius↑ down ↓ right
Ionisation energy↓ down ↑ right
Electronegativity↓ down ↑ right
Metallic character↑ down ↓ right

Beginner glossary — A to M

Atom
Smallest unit of an element that retains its chemical properties. Made of protons, neutrons, and electrons.
Atomic mass (u)
Average mass of an element's atoms, weighted by natural isotope abundance. Unit: unified atomic mass unit.
Atomic number (Z)
Number of protons in the nucleus. Uniquely identifies every element — no two elements share the same Z.
Electron
Negatively charged particle orbiting the nucleus in shells. Determines how an element behaves chemically.
Electronegativity
How strongly an atom pulls shared electrons toward itself in a bond. Fluorine is the most electronegative element.
Group (column)
Vertical column 1–18. Elements in the same group share the same number of valence electrons and have similar chemistry.
Ion
An atom that has gained or lost electrons, giving it a net electric charge. Na⁺ and Cl⁻ are common examples.
Isotope
Atoms of the same element with different numbers of neutrons. Same atomic number, different mass.
Mole (mol)
6.022 × 10²³ particles — the chemist's "dozen" for counting atoms or molecules in a usable quantity.
Molecule
Two or more atoms bonded together. H₂O (water), CO₂, and NH₃ (ammonia) are familiar examples.

Beginner glossary — N to Z + states

Neutron
Neutral particle in the nucleus. Adds to the atomic mass but does not affect charge or chemical behaviour.
Nucleus
Dense central core of an atom containing protons and neutrons. Extremely small relative to the atom's total size.
Period (row)
Horizontal row 1–7. All elements in the same period have the same number of electron shells.
Proton
Positively charged particle in the nucleus. The number of protons equals the atomic number and defines the element.
Radioactive
An unstable nucleus that emits radiation over time. Elements with masses in [brackets] have no stable isotope.
Valence electrons
Electrons in the outermost shell. These form chemical bonds with other atoms. Group number = valence electron count.
States at room temperature (25°C)
Solidmost metals + several nonmetals
LiquidHg (80), Br (35)
GasH, N, O, F, Cl + noble gases
Brackets e.g. [98]radioactive, no stable isotope
Synthetic (Z ≥ 95)Americium and above