Period 1 element | Wikipedia Easy Search

Periodic table
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Periodic table forms 18-column 32-column Alternative and extended forms
Periodic table history D. Mendeleev 1871 table 1869 predictions Discovery of elements Naming and etymology for people for places controversies (in East Asia) Systematic element names
Sets of elements
By periodic table structure Groups (1–18) 1 (alkali metals) 2 (alkaline earth metals) 3 4 5 6 7 8 9 10 11 12 13 14 15 (pnictogens) 16 (chalcogens) 17 (halogens) 18 (noble gases) Periods (1–7, ...) 1 2 3 4 5 6 7 8+ Blocks (s, p, d, f, ...) Atomic orbitals Aufbau principle
By metallic classification Metals alkali alkaline earth transition post-transition lanthanide actinide (superactinide) Metalloids dividing metals and nonmetals Nonmetals unclassified nonmetal halogen noble gas
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Elements
List of chemical elements by abundance (in human body) by atomic properties by isotope stability by symbol
Properties of elements Atomic weight Crystal structure Electron affinity configuration Electronegativity (Allen, Pauling) Goldschmidt classification Nutrition Valence
Data pages for elements Abundance Atomic radius Boiling point Critical point Density Elasticity Electrical resistivity Electron affinity / configuration Electronegativity Hardness Heat capacity / of fusion / of vaporization Ionization energy Melting point Oxidation state Speed of sound Thermal conductivity / expansion coefficient Vapor pressure
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A period 1 element is one of the chemical elements in the first row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate periodic (recurring) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that analog elements fall into the same vertical columns. The first period contains fewer elements than any other row in the table, with only two: hydrogen and helium. This situation can be explained by modern theories of atomic structure. In a quantum mechanical description of atomic structure, this period corresponds to the filling of the 1s orbital. Period 1 elements obey the duet rule in that they need two electrons to complete their valence shell.

Hydrogen and helium are the oldest and the most abundant elements in the universe.