In chemistry Chemistry is the science of matter and the changes it undergoes. The science of matter is also addressed by physics, but while physics takes a more general and fundamental approach, chemistry is more specialized, being concerned with the composition, behavior, structure, and properties of matter, as well as the changes it undergoes during chemical and physics Physics is a natural science that involves the study of matter and its motion through space-time, as well as all applicable concepts, such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves, the atomic number (also known as the proton number) is the number of protons The proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom, along with neutrons, but is also stable by itself and has a second identity as the hydrogen ion, H+. It is composed of three fundamental particles: two up quarks and one down quark found in the nucleus The nucleus is the very dense region consisting of nucleons at the center of an atom. Almost all of the mass in an atom is made up from the protons and neutrons in the nucleus, with a very small contribution from the orbiting electrons. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford of an atom The name Atom applies to a pair of related standards. The Atom Syndication Format is an XML language used for web feeds, while the Atom Publishing Protocol is a simple HTTP-based protocol for creating and updating web resources and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons. Common examples of elements are iron, copper, silver, gold, hydrogen, carbon,. In an atom of neutral charge Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields. The interaction between a moving charge and an electromagnetic field is the source of the electromagnetic force, which is one of the, the atomic number is also equal to the number of electrons The electron is a subatomic particle carrying a negative electric charge. It has no known components or substructure, and therefore is believed to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton. The intrinsic angular momentum of the electron is a half integer value in units of ħ, which means that.
The atomic number, Z, should not be confused with the mass number The mass number , also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus. Because protons and neutrons both are baryons, the mass number A is identical with the baryon number B as of the nucleus as of the whole atom or ion. The mass number is different for, A, which is the total number of protons and neutrons The neutron is a subatomic particle with no net electric charge and a mass slightly larger than that of a proton. They are usually found in atomic nuclei. The nuclei of most atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of protons in a nucleus is the atomic number and defines the type in the nucleus of an atom. The number of neutrons, N, is known as the neutron number Atomic number plus neutron number equals mass number: Z+N=A of the atom; thus, A = Z + N. Since protons and neutrons have approximately the same mass (and the mass of the electrons is negligible Negligible refers to the quantities so small that they can be ignored when studying the larger effect. Although related to the more mathematical concepts of infinitesimal, the idea of negligibility is particularly useful in practical disciplines like physics, chemistry, mechanical and electronic engineering, computer programming and in everyday for many purposes), the atomic mass The atomic mass 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 of protons, neutrons and electrons in a single atom (when the atom is motionless). The atomic mass is sometimes incorrectly used as a synonym of relative atomic mass, average atomic mass and atomic of an atom is roughly equal to A.
Atoms having the same atomic number Z but different neutron number N, and hence different atomic mass, are known as isotopes Isotopes are different types of atoms of the same chemical element, each having a different number of neutrons. In a corresponding manner, isotopes differ in mass number (or number of nucleons) but never in atomic number. The number of protons (the atomic number) is the same because that is what characterizes a chemical element. For example,. Most naturally occurring elements exist as a mixture of isotopes, and the average atomic mass of this mixture determines the element's atomic weight Atomic weight is a dimensionless physical quantity, the ratio of the average mass of atoms of an element (from a given source) to 1/12 of the mass of an atom of carbon-12 (known as the unified atomic mass unit). The term is usually used, without further qualification, to refer to the standard atomic weights published at regular intervals by the.
Contents |
History
Loosely speaking, the existence of a periodic table The periodic table of the chemical elements is a tabular display of the chemical elements. Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869, who intended the table to illustrate recurring ("periodic") trends in the properties of the elements. The layout of the table creates an ordering for the elements. Such an ordering is not necessarily a numbering, but can be used to construct a numbering by fiat. Dmitri Mendeleev Dmitri Ivanovich Mendeleev (also romanized Mendeleyev or Mendeleef; Russian: Дми́трий Ива́нович Менделе́ев listen ) (8 February [O.S. 27 January] 1834 – 2 February [O.S. 20 January] 1907), was a Russian chemist and inventor. He is credited as being the creator of the first version of the periodic table of elements claimed he arranged his tables in order of atomic weight Atomic weight is a dimensionless physical quantity, the ratio of the average mass of atoms of an element (from a given source) to 1/12 of the mass of an atom of carbon-12 (known as the unified atomic mass unit). The term is usually used, without further qualification, to refer to the standard atomic weights published at regular intervals by the ("Atomgewicht")[1] However, in deference to the observed chemical properties, he violated his own rule and placed tellurium Tellurium is a chemical element that has the symbol Te and atomic number 52. A brittle, mildly toxic, silver-white metalloid which looks similar to tin, tellurium is chemically related to selenium and sulfur. Tellurium was discovered in 1782 by Franz-Joseph Müller von Reichenstein in a mineral containing gold and tellurium. Martin Heinrich (atomic weight 127.6) ahead of iodine Iodine , from Greek: ιώδης iodes, meaning violet or purple, is a chemical element that has the symbol I and the atomic number 53 (atomic weight 126.9).[1][2] This placement is consistent with the modern practice of ordering the elements by proton number, Z, but this number was not known or suspected at the time.
A simple numbering based on periodic table position was never entirely satisfactory. Besides iodine and tellurium, several other pairs of elements (such as cobalt and nickel) were known to have nearly identical or reversed atomic weights, leaving their placement in the periodic table by chemical properties to be in violation of known physical properties. Another problem was that the gradual identification of more and more chemically similar and indistinguishable lanthanides The lanthanide or lanthanoid series comprises the fourteen elements with atomic numbers 58 through 71, from cerium to lutetium. All lanthanides are f-block elements, corresponding to the filling of the 4f electron shell. Lanthanum, which is a d-block element, may also be considered to be a lanthanide. All lanthanide elements form trivalent cations,, which were of an uncertain number, led to inconsistency and uncertainty in the numbering of all elements at least from lutetium Lutetium is a chemical element with the symbol Lu and atomic number 71. It is in the d-block of the periodic table, not the f-block, but the IUPAC classifies it as a lanthanide. It is one of the elements that traditionally were included in the classification, "rare earths". One of its radioactive isotopes is used in nuclear technology to (element 71) onwards (hafnium Hafnium is a chemical element with the symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869. Hafnium was the penultimate stable isotope element to be discovered . Hafnium was found by was not known at this time).
In 1911 Ernest Rutherford Ernest Rutherford, 1st Baron Rutherford of Nelson, OM, FRS was a British-New Zealand chemist and physicist who became known as the father of nuclear physics. In early work he discovered the concept of radioactive half life, proved that radioactivity involved the transmutation of one chemical element to another, and also differentiated and named gave a model of the atom in which a central core held most of the atom's mass and a positive charge which, in units of the electron's charge, was to be approximately equal to half of the atom's atomic weight, expressed in numbers of hydrogen atoms. This central charge would thus be approximately half the atomic weight (though it was almost 25% off the figure for the atomic number in gold (Z = 79, A = 197), the single element from which Rutherford made his guess). Nevertheless, in spite of Rutherford's estimation that gold had a central charge of about 100 (but was element Z=79 on the periodic table), a month after Rutherford's paper appeared, Antonius van den Broek first formally suggested that the central charge and number of electrons in an atom was exactly equal to its place in the periodic table (also known as element number, atomic number, and symbolized Z). This proved eventually to be the case.
The experimental situation improved dramatically after research by Henry Moseley in 1913.[3] Moseley, after discussions with Bohr who was at the same lab (and who had used Van den Broek's hypothesis in his Bohr model In atomic physics, the Bohr model, devised by Niels Bohr, depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravity. This was an improvement on the earlier cubic of the atom), decided to test Van den Broek and Bohr's hypothesis directly, by seeing if spectral lines emitted from excited atoms fit the Bohr theory's demand that the frequency of the spectral lines be proportional to a measure of the square of Z.
To do this, Moseley measured the wavelengths of the innermost photon transitions (K and L lines) produced by the elements from aluminum (Z = 13) to gold (Z = 79) used as a series of movable anodic targets inside an x-ray tube An X-ray tube is a vacuum tube that produces X-rays. They are used in X-ray machines. X-rays are part of the electromagnetic spectrum, an ionizing radiation with wavelengths shorter than ultraviolet light. X-ray tubes evolved from experimental Crookes tubes with which X-rays were first discovered in the late 1800s, and the availability of this.[4] The square root of the frequency of these photons (x-rays) increased from one target to the next in a linear fashion. This led to the conclusion (Moseley's law) that the atomic number does closely correspond (with an offset of one unit for K-lines, in Moseley's work) to the calculated electric charge Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields. The interaction between a moving charge and an electromagnetic field is the source of the electromagnetic force, which is one of the of the nucleus, i.e. the proton number Z. Among other things, Moseley demonstrated that the lanthanide The lanthanide or lanthanoid series comprises the fourteen elements with atomic numbers 58 through 71, from cerium to lutetium. All lanthanides are f-block elements, corresponding to the filling of the 4f electron shell. Lanthanum, which is a d-block element, may also be considered to be a lanthanide. All lanthanide elements form trivalent cations, series (from lanthanum Lanthanum is a chemical element with the symbol La and atomic number 57. Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is a lanthanide. It is found in some rare-earth minerals, usually in combination with cerium and other rare earth elements. Lanthanum is a malleable, ductile, and soft metal that to lutetium Lutetium is a chemical element with the symbol Lu and atomic number 71. It is in the d-block of the periodic table, not the f-block, but the IUPAC classifies it as a lanthanide. It is one of the elements that traditionally were included in the classification, "rare earths". One of its radioactive isotopes is used in nuclear technology to inclusive) must have 15 members — no fewer and no more — which was far from obvious from the chemistry at that time.
The conventional symbol Z presumably comes from the German word Atomzahl (atomic number).[5]
Chemical properties
Each element has a specific set of chemical properties as a consequence of the number of electrons present in the neutral atom, which is Z. The configuration In atomic physics and quantum chemistry, electron configuration is the arrangement of electrons of an atom, a molecule, or other physical structure. It concerns the way electrons can be distributed in the orbitals of the given system of these electrons follows from the principles of quantum mechanics Quantum mechanics , also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic scales. In advanced topics of QM, some of these. The number of electrons in each element's electron shells An electron shell may be thought of as an orbit followed by electrons around an atom nucleus. Because each shell can contain only a fixed number of electrons, each shell is associated with a particular range of electron energy, and thus each shell must fill completely before electrons can be added to an outer shell. The electrons in the outermost, particularly the outermost valence shell An electron shell may be thought of as an orbit followed by electrons around an atom nucleus. Because each shell can contain only a fixed number of electrons, each shell is associated with a particular range of electron energy, and thus each shell must fill completely before electrons can be added to an outer shell. The electrons in the outermost, is the primary factor in determining its chemical bonding A chemical bond is an interaction between atoms or molecules and allows the formation of polyatomic chemical compounds. A chemical bond is the attraction caused by the electromagnetic force between opposing charges, either between electrons and nuclei, or as the result of a dipole attraction. The strength of bonds varies considerably; there are & behavior. Hence it is the atomic number alone that determines the chemical properties of an element; and it is for this reason that an element can be defined as consisting of any mixture of atoms with a given atomic number.
New elements
The quest for new elements is usually described using atomic numbers. As of 2010, elements with atomic numbers 1 to 118 have been observed. 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 Half-life is the period of time it takes for a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but may apply to any quantity which follows a set-rate decay becomes shorter as atomic number increases, though an "island of stability The island of stability is a term from nuclear physics that describes the possibility of elements with particularly stable "magic numbers" of protons and neutrons. This would allow certain isotopes of some transuranic elements to be far more stable than others; that is, decay much more slowly" may exist for undiscovered isotopes with certain numbers of protons and neutrons.
See also
- History of the periodic table The history of the periodic table reflects over a century of growth in the understanding of chemical properties, and culminates with the publication of the first actual periodic table by Dmitri Mendeleev in 1869. While Mendeleev built upon earlier discoveries by such scientists as Antoine-Laurent de Lavoisier, the Russian scientist is generally
- Effective atomic number
- Atomic theory In chemistry and physics, atomic theory is a theory of the nature of matter, which states that matter is composed of discrete units called atoms, as opposed to the obsolete notion that matter could be divided into any arbitrarily small quantity. It began as a philosophical concept in ancient Greece and India and entered the scientific mainstream
- Prout's hypothesis 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 atom. In 1815 and 1816, the English chemist William Prout published two papers in which he observed that the atomic weights that had been measured for the elements known at that
Notes
- ^ a b The Periodic Table of Elements (American Institute of Physics)
- ^ The Development of the Periodic Table (Chemsoc)
- ^ Ordering the Elements in the Periodic Table (Chemsoc)
- ^ http://www.chemistry.co.nz/henry_moseley_article.htm Moseley's paper with illustrations
- ^ Origin of symbol Z
Categories: Chemical properties | Nuclear physics Categories: Atomic physics | Particle physics | Quantum mechanics
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