See also: List of elements by atomic number

In chemistry and physics, the atomic number (also known as the proton number) is the number of protons found in the nucleus of an atom. A table of Chemical elements ordered by Atomic number and color coded according to type of element Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive The nucleus of an Atom is the very dense region consisting of Nucleons ( Protons and Neutrons, at the center of an atom History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny It is traditionally represented by the symbol Z. The atomic number uniquely identifies a chemical element. A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. In an atom of neutral charge, atomic number is equal to the number of electrons. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J

The atomic number is closely related to the mass number, which is the total number of protons and neutrons in the nucleus of an atom. The mass number ( A) also called atomic mass number or nucleon number, is the total number of Protons and Neutrons (together known as This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron.

Contents 1 History 2 Chemical properties 3 New elements 4 See also 5 Notes

History

The atomic number originally was used to signify the element's location in the periodic table. The periodic table of the chemical elements is a tabular method of displaying the Chemical elements Although precursors to this table exist its invention is Dmitri Mendeleev arranged the known elements in increasing order of atomic weight and grouped by their similar chemical properties. Dmitri Ivanovich Mendeleev (sometimes spelled Mendeleyev; Дми́трий Ива́нович Менделе́ев) ( &ndash) was a Russian chemist and The atomic mass (ma is the Mass of an atom most often expressed in unified atomic mass units The atomic mass may be considered to be the total mass ^[1] However, placing the elements in strict order of atomic weight resulted in some mismatches. Iodine and tellurium, if listed by atomic weight, appeared to be in the wrong order; and would fit better by chemical properties if their places in the table were swapped. Iodine (ˈaɪədaɪn ˈaɪədɪn or /ˈaɪədiːn/ from ιώδης iodes "violet" is a Chemical element that has the symbol I and Atomic Tellurium (tɪˈlʊəriəm/ /tɛl- is a Chemical element that has the symbol Te and Atomic number 52 ^[2] Placing them in the order which fit their properties most closely, their number in the table was their atomic number. This number appeared to be related to the mass of the atom but, as the discrepancy showed, reflected some property other than mass.

The anomalies in this sequence were finally explained after research by Henry Gwyn Jeffreys Moseley in 1913. Henry Gwyn Jeffreys Moseley ( November 23, 1887 – August 10, 1915) was an English physicist. ^[3] Moseley discovered a strict relationship between the x-ray diffraction spectra of elements, and their correct location in the periodic table. X-ray scattering techniques are a family of non-destructive analytical techniques which reveal information about the crystallographic structure chemical composition This led to the conclusion that the atomic number corresponds to the electric charge of the nucleus—the charge of the protons. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. The atomic number is the number of protons that is equal to the number of electrons. The proton charge is positive and the electron charge is negative.

Chemical properties

Each element has a specific set of chemical properties as a consequence of the number of protons in its nucleus. The charge of an atom's nucleus defines its electron configuration based on principles of quantum mechanics. In Atomic physics and Quantum chemistry, electron configuration is the arrangement of Electrons in an Atom, Molecule, or other Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons The form of each element's electron shells, particularly the valence shell, is the primary factor in determining its chemical bonding behavior. An electron shell may be crudely thought of as an Orbit followed by Electrons around an Atom nucleus. An electron shell may be crudely thought of as an Orbit followed by Electrons around an Atom nucleus. A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic

New elements

The quest for new elements is usually described using atomic number. As of early 2007, elements with atomic numbers through 118 (excluding 117) have been discovered. Synthesis of new elements is accomplished by bombarding target atoms of heavy elements with ions, such that the sum of the atomic numbers of the target and ion elements equals the atomic number of the element being created. In general, the half-life becomes shorter as atomic number increases, though an "island of stability" may exist for undiscovered isotopes with certain numbers of protons and neutrons. Half-Life (computer-game page here It's already listed in the disambiguation page The island of stability is a term from Nuclear physics that describes the possibility of elements with particularly stable " magic numbers "

See also

• History of the periodic table
• Effective atomic number
• Atomic Theory
• Prout's hypothesis

Notes

The Periodic table is a tabular method of displaying the chemical elements Effective atomic number has two different meanings one that is the effective nuclear charge of an atom and one that calculates the average Atomic number for a compound or mixture This article focuses on the historical models of the atom For a history of the study of how atoms combine to form molecules see History of the molecule. Prout's hypothesis was an early 19th century attempt to explain the existence of the various Chemical elements through a hypothesis regarding the internal structure of the

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