Interactive Periodic Table

How to use this tool

1. Search by element name, symbol, atomic number, or category.
2. Click on an element to see its properties.

How to read the periodic table

Each element cell typically shows:

• Atomic number: the number of protons in the nucleus (defines the element)
• Symbol: 1–3 letter abbreviation (H, He, Li, Na, Fe...)
• Atomic mass: weighted average of naturally occurring isotopes when a standard atomic weight is available

Organization

• Periods (rows): elements in the same period have the same number of electron shells.
• Groups (columns): elements in the same group have the same number of valence electrons and similar chemical properties.
• Blocks: s, p, d, f blocks correspond to which subshell the outermost electrons occupy.

Special groups

• Group 1 (Alkali metals): highly reactive; 1 valence electron
• Group 17 (Halogens): very reactive nonmetals; form salts with metals
• Group 18 (Noble gases): largely inert; complete outer electron shells

Periodic trends

Several properties change predictably across rows and columns:

Discovery timeline highlights

• 1669: Phosphorus - first element isolated by a known individual (Hennig Brandt)
• 1869: Dmitri Mendeleev publishes the first periodic table, predicting gaps for undiscovered elements
• 1898: Pierre and Marie Curie discover Polonium and Radium
• 1940: Plutonium synthesized - first transuranic element (Glenn Seaborg's team)
• 2016: Four new elements (113–118) officially named: Nihonium, Moscovium, Tennessine, Oganesson

Reading atomic mass

Atomic mass (also called atomic weight) is a weighted average of an element's isotopes when a standard atomic weight can be determined. For example, chlorine has two stable isotopes: ³⁵Cl (75.77%) and ³⁷Cl (24.23%), giving an average atomic mass of about 35.45 u. Some radioactive elements without a standard atomic weight are instead shown with the mass number of a representative isotope in square brackets: Technetium [98] and Promethium [145] are examples. Radioactivity alone does not determine the notation: Bismuth has a standard atomic weight (208.98), as do Thorium and Uranium, so their values are not bracketed here.