The periodic table reference shows key elements with atomic number, symbol, mass, electron configuration, and common uses. Click any element for details. Search by name, symbol, or atomic number.
About the Periodic Table
The periodic table organizes all known chemical elements by atomic number (number of protons), electron configuration, and recurring chemical properties. Dmitri Mendeleev created the first widely recognized version in 1869. The modern table has 118 confirmed elements, from hydrogen (1) to oganesson (118).
How to read an element entry
Each element box shows the atomic number (top left), chemical symbol (1-2 letters), element name, and atomic mass (weighted average of isotopes). The color indicates the element category. Atomic mass in parentheses indicates the most stable isotope (for radioactive elements).
Frequently Asked Questions
How many elements are in the periodic table?
There are 118 confirmed elements in the modern periodic table, from hydrogen (atomic number 1) to oganesson (atomic number 118). Elements 1-94 occur naturally; elements 95-118 are synthesized.
What does the atomic number mean?
The atomic number is the number of protons in an atom's nucleus. It uniquely defines the element — every atom of carbon has exactly 6 protons, every atom of gold has exactly 79 protons. The atomic number also equals the number of electrons in a neutral atom.
What is atomic mass?
Atomic mass is the weighted average mass of all naturally occurring isotopes of an element, measured in atomic mass units (amu). It differs from atomic number because neutrons contribute to mass but not to atomic number. Carbon's atomic mass of 12.011 reflects a mix of C-12 and C-13 isotopes.
What are the categories of elements?
Elements are categorized as: alkali metals, alkaline earth metals, transition metals, post-transition metals, metalloids, nonmetals, halogens, noble gases, lanthanides, and actinides. The category affects chemical behavior and physical properties.
Is this periodic table free?
Yes, completely free and no signup required.