Interactive Periodic Table of Elements
The periodic table arranges all 118 known elements by atomic number, so elements in the same column (group) have similar chemistry. Hover or tap any element to see its atomic mass, electron configuration and physical properties.
- Alkali metal
- Alkaline earth metal
- Transition metal
- Post-transition metal
- Metalloid
- Reactive nonmetal
- Noble gas
- Lanthanide
- Actinide
- Unknown properties
Iron
Transition metal
- Atomic number
- 26
- Atomic mass
- 55.845 g/mol
- Electron configuration
- [Ar] 3d⁶ 4s²
- Group · period · block
- 8 · 4 · d
- Electronegativity (Pauling)
- 1.83
- State at room temperature
- Solid
- Melting point
- 1,537.9 °C / 2,800.1 °F
- Boiling point
- 2,860.9 °C / 5,181.5 °F
- Density
- 7.874 g/cm³
How the periodic table is organized
Elements are placed in order of atomic number, which is the number of protons in the nucleus. Each row is a period: a new period starts whenever a new electron shell begins to fill, so hydrogen and helium sit alone in period 1, and periods 6 and 7 are long enough that the lanthanides and actinides are split off into the two rows at the bottom to keep the table a sensible width.
Each column is a group. Elements in a group have the same number of electrons in their outer shell, which is why they behave alike: the group 1 alkali metals all react vigorously with water, and the group 18 noble gases barely react at all.
The table is also divided into blocks named after the orbital being filled. Groups 1 and 2 (plus helium) make up the s-block, groups 13 to 18 the p-block, the transition metals the d-block, and the lanthanides and actinides the f-block. Switch the coloring to Block above to see them.
Reading an element's details
Atomic mass is the average mass of an element's atoms, weighted by how common each isotope is in nature, in grams per mole. It's the number you use to find a compound's molar mass. Elements with no stable isotopes have no standard atomic weight, so the table shows the mass number of the longest-lived known isotope in [square brackets] instead.
The electron configuration lists which orbitals the electrons occupy. The shorthand starts from the previous noble gas, so iron's [Ar] 3d⁶ 4s² means "argon's 18 electrons, then 6 in the 3d orbitals and 2 in the 4s". Electronegativity, on the Pauling scale, measures how strongly an atom pulls on shared electrons: fluorine is the highest at 3.98, and the alkali metals on the left are the lowest.
Melting and boiling points are given at normal atmospheric pressure, and density is in grams per cubic centimeter for solids and liquids and grams per liter for gases. Many values for the heaviest elements are unknown because only a handful of atoms have ever been made, and they decay within seconds.
Frequently asked questions
- How many elements are on the periodic table?
- 118. The last four, nihonium (113), moscovium (115), tennessine (117) and oganesson (118), were officially named in 2016, which completed the seventh row.
- Why are the lanthanides and actinides shown separately?
- They belong in periods 6 and 7 between groups 2 and 3, but including them inline would make the table 32 columns wide. Pulling them out underneath is a layout choice; the dashed 57–71 and 89–103 boxes mark where they fit.
- Why are some atomic masses in square brackets?
- Those elements have no stable isotopes and so no fixed natural mix to average over. The bracketed number is the mass number of the longest-lived isotope, which is the conventional value used in calculations.
- Which elements are liquid at room temperature?
- Only mercury and bromine. Gallium and cesium melt just above room temperature (about 30 °C and 28 °C), so gallium will melt in your hand.
- What is the most electronegative element?
- Fluorine, at 3.98 on the Pauling scale. Electronegativity generally increases from left to right across a period and decreases going down a group.