Interactive Periodic Table
Click any element to explore its properties
The Periodic Table of Elements
The periodic table organises all 118 known chemical elements by increasing atomic number. Elements in the same column (group) share similar chemical properties because they have the same number of valence electrons. Elements in the same row (period) have the same number of electron shells.
Groups and Periods
The 18 vertical columns are called groups. Group 1 contains the alkali metals (Li, Na, K…), Group 17 the halogens (F, Cl, Br…), and Group 18 the noble gases (He, Ne, Ar…). The 7 horizontal rows are called periods. As you move across a period from left to right, atomic number increases and elements transition from metals to metalloids to nonmetals.
Periodic Trends
Atomic Radius
Increases down a group (more electron shells) and decreases across a period (stronger nuclear charge pulls electrons closer).
Electronegativity
Increases across a period and decreases down a group. Fluorine (3.98) is the most electronegative element.
Ionization Energy
Increases across a period and decreases down a group. Noble gases have the highest ionization energies in each period.
Electron Affinity
Generally increases across a period. Halogens have the highest electron affinities because they need just one electron to complete their valence shell.
Element Categories
Elements are classified into categories based on their physical and chemical properties. Metals (alkali metals, alkaline earth metals, transition metals, post-transition metals, lanthanides, actinides) are generally shiny, conduct electricity, and form positive ions. Nonmetals are poor conductors and tend to gain electrons. Metalloids (B, Si, Ge, As, Sb, Te) have properties intermediate between metals and nonmetals and are widely used as semiconductors.
Lanthanides and Actinides
The lanthanides (elements 57–71) and actinides (elements 89–103) are placed below the main table to keep it compact. Lanthanides are used in magnets, lasers, and catalytic converters. Actinides include uranium and plutonium, which are critical for nuclear energy and research.
History of the Periodic Table
Dmitri Mendeleev published the first widely recognised periodic table in 1869, arranging elements by atomic weight and predicting the existence of undiscovered elements. Henry Moseley later reordered the table by atomic number (1913), which resolved inconsistencies in Mendeleev's arrangement. Today the table contains 118 confirmed elements, with oganesson (Og, 118) being the most recently named.
More Chemistry Tools
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