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This is a list of chemical elements and their atomic properties, ordered by atomic number (Z).. Since valence electrons are not clearly defined for the d-block and f-block elements, there not being a clear point at which further ionisation becomes unprofitable, a purely formal definition as number of electrons in the outermost shell has been used.
Each distinct atomic number therefore corresponds to a class of atom: these classes are called the chemical elements. [5] The chemical elements are what the periodic table classifies and organizes. Hydrogen is the element with atomic number 1; helium, atomic number 2; lithium, atomic number 3; and so on.
118 chemical elements have been identified and named officially by IUPAC.A chemical element, often simply called an element, is a type of atom which has a specific number of protons in its atomic nucleus (i.e., a specific atomic number, or Z).
Element Origin of name [1] [2] Group Period Block Standard atomic weight A r °(E) [a] Density [b] [c] Melting point [d] Boiling point [e] Specific heat capacity [f] Electronegativity [g] Abundance in Earth's crust [h] Origin [i] Phase at r.t. [j] Atomic number Z Symbol Name ( g / cm 3 ) (K) ( J / g · K ) ( mg / kg ) 1 H ...
Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to its heavier homologues strontium and barium.
Copernicium is a synthetic chemical element; it has symbol Cn and atomic number 112. Its known isotopes are extremely radioactive , and have only been created in a laboratory. The most stable known isotope , copernicium-285, has a half-life of approximately 30 seconds.
[15] 89 Y has a mass number close to 90 and has 50 neutrons in its nucleus. At least 32 synthetic isotopes of yttrium have been observed, and these range in atomic mass number from 76 to 108. [30] The least stable of these is 109 Y with a half-life of 25 ms and the most stable is 88 Y with half-life 106.629 days. [31]
The lightest elements are hydrogen and helium, both created by Big Bang nucleosynthesis in the first 20 minutes of the universe [3] in a ratio of around 3:1 by mass (or 12:1 by number of atoms), [4] [5] along with tiny traces of the next two elements, lithium and beryllium.
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