Atomic number
The whole number is the proton count. It uniquely identifies the element and determines the table order.
Chemical element reference
Periodic Table of Elements
Explore all 118 elements with names, atomic numbers, atomic masses, common charges, electron configurations, phases, and key physical properties.
- Elements
- 118
- Groups
- 18
- Periods
- 7
- Data review
- Aug 2026
118 elements
Interactive periodic table of the elements
123456789101112131415161718123456757-7189-103LanthanidesActinides
Quick answer
What is the periodic table?
The periodic table organizes chemical elements by increasing atomic number. Its rows, called periods, track repeating electron-shell patterns; its 18 columns, called groups, collect elements with related valence structures and chemical behavior. Position is not merely a filing system: it helps predict bonding, reactivity, atomic size, and ion formation.
Foundations
How to read the periodic table
Each position and number communicates a different piece of atomic structure.
Chemical symbol
The one- or two-letter symbol is the compact notation used in formulas and chemical equations.
Atomic mass
For naturally occurring elements, this is generally the abundance-weighted mass of their isotopes in atomic mass units.
Groups and periods
Groups run vertically from 1 to 18. Periods run horizontally from 1 to 7 and correspond to principal electron shells.
Family reference
Periodic table groups and common charges
Common oxidation states are useful patterns, but actual charge depends on the compound and bonding environment.
| Group | Family | Common oxidation states | Valence electrons |
|---|---|---|---|
| 1 | Alkali metals | +1 | 1 |
| 2 | Alkaline earth metals | +2 | 2 |
| 3-12 | Transition metals | Variable | 2 (often) |
| 13 | Boron group | +3 | 3 |
| 14 | Carbon group | +4, +2, -4 | 4 |
| 15 | Pnictogens | -3, +3, +5 | 5 |
| 16 | Chalcogens | -2, +4, +6 | 6 |
| 17 | Halogens | -1, +1, +5, +7 | 7 |
| 18 | Noble gases | 0 (usually) | 8 (He: 2) |
Patterns
Periodic trends at a glance
These broad directions describe the main-group pattern. Electron structure creates important exceptions.
Top leftTop rightBottom leftBottom right
Electronegativity
Generally increases toward fluorine.
Ionization energy
Generally increases up and to the right.
Atomic radius
Generally increases down and to the left.
Metallic character
Generally increases down and to the left.
Study reference
First 20 elements of the periodic table
The first 20 run from hydrogen to calcium and include the complete first three periods plus the start of period four.
| Atomic no. | Symbol | Element | Atomic mass | Common charges | Electron configuration |
|---|---|---|---|---|---|
| 1 | H | Hydrogen | 1.0080 | +1, -1 | 1s1 |
| 2 | He | Helium | 4.00260 | 0 | 1s2 |
| 3 | Li | Lithium | 6.94 | +1 | [He]2s1 |
| 4 | Be | Beryllium | 9.012183 | +2 | [He]2s2 |
| 5 | B | Boron | 10.81 | +3 | [He]2s2 2p1 |
| 6 | C | Carbon | 12.011 | +4, +2, -4 | [He]2s2 2p2 |
| 7 | N | Nitrogen | 14.007 | +5, +4, +3, +2, +1, -1, -2, -3 | [He] 2s2 2p3 |
| 8 | O | Oxygen | 15.999 | -2 | [He]2s2 2p4 |
| 9 | F | Fluorine | 18.998 | -1 | [He]2s2 2p5 |
| 10 | Ne | Neon | 20.180 | 0 | [He]2s2 2p6 |
| 11 | Na | Sodium | 22.990 | +1 | [Ne]3s1 |
| 12 | Mg | Magnesium | 24.305 | +2 | [Ne]3s2 |
| 13 | Al | Aluminum | 26.982 | +3 | [Ne]3s2 3p1 |
| 14 | Si | Silicon | 28.085 | +4, +2, -4 | [Ne]3s2 3p2 |
| 15 | P | Phosphorus | 30.974 | +5, +3, -3 | [Ne]3s2 3p3 |
| 16 | S | Sulfur | 32.06 | +6, +4, -2 | [Ne]3s2 3p4 |
| 17 | Cl | Chlorine | 35.45 | +7, +5, +1, -1 | [Ne]3s2 3p5 |
| 18 | Ar | Argon | 39.9 | 0 | [Ne]3s2 3p6 |
| 19 | K | Potassium | 39.098 | +1 | [Ar]4s1 |
| 20 | Ca | Calcium | 40.078 | +2 | [Ar]4s2 |
Common questions
Periodic table FAQ
How many elements are in the periodic table?
The modern periodic table contains 118 confirmed chemical elements, from hydrogen (atomic number 1) through oganesson (atomic number 118).
How is the periodic table arranged?
Elements are ordered by increasing atomic number, which is the number of protons in the nucleus. Rows are periods and columns are groups. Elements in a group often share valence-electron patterns and chemical behavior.
What are groups and periods?
A group is one of the 18 vertical columns. A period is one of the seven horizontal rows. The two detached rows are the lanthanide and actinide series from periods 6 and 7.
What does atomic mass mean on the periodic table?
For most elements, the displayed atomic mass is a weighted average based on naturally occurring isotopes. Radioactive elements without a standard atomic weight are represented by an isotope mass value in the source data.
What do the charges on the periodic table mean?
The listed charges are common oxidation states, not a promise that an element always forms one ion. Transition metals commonly have several oxidation states, while many main-group elements follow more predictable patterns.
Who created the periodic table?
Dmitri Mendeleev is most often credited with the periodic table. In 1869 he arranged known elements by recurring properties, left gaps, and successfully predicted properties of elements that had not yet been discovered.
Sources and data method
Element properties use the PubChem periodic table snapshot retrieved August 29, 2026. Names, group numbering, and standard atomic-weight context are checked against the IUPAC Periodic Table. Isotope context is cross-referenced with NIST isotopic composition data.
Last reviewed August 29, 2026 · Values marked unavailable are not replaced with estimates.