化学英文介绍

A. 绿色化学 英文介绍 the green chemistry

楼上那个是绿色化学专业系统，不是绿色化学...

Green chemistry

This article is about the concept of the environmentally friendly design of chemical procts and processes.

Green chemistry, also called sustainable chemistry, is a chemical philosophy encouraging the design of procts and processes that rece or eliminate the use and generation of hazardous substances. Whereas environmental chemistry is the chemistry of the natural environment, and of pollutant chemicals in nature, green chemistry seeks to rece and prevent pollution at its source. In 1990 the Pollution Prevention Act was passed in the United States. This act helped create a mos operandi for dealing with pollution in an original and innovative way. It aims to avoid problems before they happen.

As a chemical philosophy, green chemistry derives from organic chemistry, inorganic chemistry, biochemistry, analytical chemistry, and even physical chemistry. However, the philosophy of green chemistry tends to focus on instrial applications. Click chemistry is often cited as a style of chemical synthesis that is consistent with the goals of green chemistry. The focus is on minimizing the hazard and maximizing the efficiency of any chemical choice. It is distinct from environmental chemistry which focuses on chemical phenomena in the environment.

In 2005 Ryoji Noyori identified three key developments in green chemistry: use of supercritical carbon dioxide as green solvent, aqueous hydrogen peroxide for clean oxidations and the use of hydrogen in asymmetric synthesis.[1] Examples of applied green chemistry are supercritical water oxidation, on water reactions and dry media reactions.

Bioengineering is also seen as a promising technique for achieving green chemistry goals. A number of important process chemicals can be synthesized in engineered organisms, such as shikimate, a Tamiflu precursor which is fermented by Roche in bacteria.

B. 英文介绍化学元素铅

性质
Lead is bright and silvery when freshly cut but the surface rapidly tarnishes in air to proce the more commonly observed ll luster normally associated with lead. It is a dense, ctile, very soft, highly malleable, bluish-white metal that has poor electrical conctivity. This true metal is highly resistant to corrosion, and because of this property, it is used to contain corrosive liquids (e.g., sulfuric acid). Because lead is very malleable and resistant to corrosion it is extensively used in building construction, e.g., external coverings of roofing joints. Lead can be toughened by addition of a small amount of antimony or other metals. All lead, except 204Pb, is the end proct of a complex radioactive decay. Lead is also poisonous, as are its compounds.
这段是同位素
Lead has many isotopes but 4 stable ones. The 4 stable isotopes are204Pb, 206Pb, 207Pb and 208Pb with 204Pb regarded as primordial Pb and 206, 207, 208 are formed from decay of U and Th. The one common radiogenic isotope, 202Pb, has a half-life of approximately 53,000 years.[1]

这一段是历史
Lead has been commonly used for thousands of years because it is widespread, easy to extract and easy to work with. It is highly malleable and ctile as well as easy to smelt. Metallic lead beads dating back to 6400 B.C. have been found in Çatalhöyük in modern-day Turkey.[7] In the early Bronze Age, lead was used with antimony and arsenic. Lead is mentioned in the Book of Exos (15:10).
In alchemy, lead was thought to be the oldest metal and was associated with the planet Saturn. Lead pipes that bear the insignia of Roman emperors are still in service[citation needed] and many Roman "pigs" (ingots) of lead figure in Derbyshire lead mining history and in the history of the instry in other English centers. The Romans also used lead in molten form to secure iron pins that held together large limestone blocks in certain monumental buildings. Lead's symbol Pb is an abbreviation of its Latin name plumbum for soft metals; originally it was plumbum nigrum (literally, "black plumbum"), where plumbum candim (literally, "bright plumbum") was tin. The English words "plumbing", "plumber", "plumb", and "plumb-bob" also derive from this Latin root.

生产和回收
Proction and recycling
Proction and consumption of lead is increasing worldwide. Total annual proction is about 8 million tonnes; about half is proced from recycled scrap. The top lead procing countries, as of 2008, are Australia, China, USA, Peru, Canada, Mexico, Sweden, Morocco, South Africa and North Korea.[10] Australia, China and the United States account for more than half of primary proction.[11]
2008 mine proction: 3,886,000 tonnes
2008 metal proction: 8,725,000 tonnes
2008 metal consumption: 8,706,000 tonnes[12]
At current use rates, the supply of lead is estimated to run out in 42 years.[13] Environmental analyst, Lester Brown, however, has suggested lead could run out within 18 years based on an extrapolation of 2% growth per year.[14] This may need to be reviewed to take account of renewed interest in recycling, and rapid progress in fuel cell technology.

这段是实际应用
Lead is a major constituent of the lead-acid battery used extensively as a car battery.[15]
Lead is used as a coloring element in ceramic glazes, notably in the colors red and yellow.[16]
Lead is used to form glazing bars for stained glass or other multi-lit windows. The practice has become less common, not for danger but for stylistic reasons.
Lead is frequently used in polyvinyl chloride (PVC) plastic, which coats electrical cords.[17][18]
Lead is used as projectiles for firearms and fishing sinkers because of its density, low cost compared to alternative procts and ease of use e to relatively low melting point.[19]
Lead, or sheet-lead, is used as a sound deadening layer in such areas as wall, floor and ceiling design in sound studios where levels of airborne and mechanically proced sound are targeted for rection or virtual elimination.[20][21]
Lead is used in some candles to treat the wick to ensure a longer, more even burn. Because of the dangers, European and North American manufacturers use more expensive alternatives such as zinc.[22][23]
Lead is used as shielding from radiation (e.g., in X-ray rooms).[24]
Molten lead is used as a coolant (e.g., for lead cooled fast reactors).[25]
Lead glass is composed of 12-28% lead oxide. It changes the optical characteristics of the glass and reces the transmission of radiation.[26]
Lead is the traditional base metal of organ pipes, mixed with varying amounts of tin to control the tone of the pipe.[27][28]
Lead is used as electrodes in the process of electrolysis.
Lead is used in solder for electronics, although this usage is being phased out by some countries to rece the amount of environmentally unfriendly waste.
Lead is used in high voltage power cables as sheathing material to prevent water diffusion into insulation.
Lead is added to brass to rece machine tool wear.
Some artists using oil-based paints continue to use lead carbonate white, citing its properties in comparison with the alternatives.
Lead, in the form of strips, or tape, is used for the customization of tennis rackets. Tennis rackets of the past sometimes had lead added to them by the manufacturer to increase weight.[29]
Lead has many uses in the construction instry (e.g., lead sheets are used as architectural metals in roofing material, cladding, flashings, gutters and gutter joints, and on roof parapets). Detailed lead moldings are used as decorative motifs used to fix lead sheet.
Lead is still widely used in statues and sculptures.
Tetra-ethyl lead is used as an anti-knock additive for aviation fuel in piston driven aircraft.
Lead-based semiconctors, such as lead telluride, lead selenide and lead antimonide are finding applications in photovoltaic (solar energy) cells and infrared detectors.[30]
Lead is often used to balance the wheels of a car; this use is being phased out in favor of other materials for environmental reasons.

C. 鍖栧︾殑鑻辨枃鑷鎴戜粙缁

銆銆鍖栧︽槸鑷鐒剁戝︾殑涓绉嶏紝鍦ㄥ垎瀛愩佸師瀛愬眰娆′笂鐮旂┒鐗╄川鐨勭粍鎴愩佹ц川銆佺粨鏋勪笌鍙樺寲瑙勫緥;鍒涢犳柊鐗╄川鐨勭戝︺傞偅涔堝叧浜庡寲瀛︾殑鑻辫鑷鎴戜粙缁嶆湁鍝浜涘憿?涓嬮潰鎴戜负浣犳暣鐞嗕簡鍖栧︾殑鑻辨枃鑷鎴戜粙缁嶏紝娆㈣繋闃呰汇

銆銆鍖栧︾殑鑻辨枃鑷鎴戜粙缁嶃绡囥1銆

銆銆Good morning! My name is XXX. It is really my honor to have this opportunity for an interview. I hope I can make a good performance today. I’m confident I can succeed. Now I will introce myself briefly. I am 26 years old and born in XXX province.

銆銆I’ll graate from XX University. My major is XXX. I’ll receive my master degree in the next year. During university, I spent most of my time on study so that I have passed CET-6 and acquired basic knowledge of my major. In three years, I almost do experiments in lab every day.

銆銆So I master the basic operation of chemical experiments and performance of chemicals. It’s easy for me to accomplish chemical experiments independently. I can use apparatus of GC-MS, HNMR, IR and so on to test the procts’ structures. Generally speaking, I am an outgoing person. I enjoy mixing and doing things with others. As a vic-chairman, some other members and me have organized diathesis developing activity together. I have strong sense of responsibility and mange capability.

銆銆I’m quite active and energetic. I approach things enthusiastically and I don’t like leaving things half done. I’m a tutor teacher. So I have much more patience than some other people. I persist in jogging every evening. So I have strong will power and good habit. I hope I can get this job. That’s all. Thank you for giving me the chance.

銆銆鍖栧︾殑鑻辨枃鑷鎴戜粙缁嶃绡囥2銆

銆銆My name is XXX.I am twenty-eight years old. In 1986 I received my M.S. in Chemistry from the University of California. As a student I took many Chemistry and Biology courses a few of which are listed here:General Chemistry Organic chemistry Physical Chemistry Biochemistry - two years Analytical Chemistry - both organic and Inorganic As I was a graate student, I worked as a research assistant for Dr. John Williams, Professor of biochemistry, University of California. During this time I assisted Dr. Williams in basic researh concerning the phosphates cycle in metabolism. I can supply u with a of the resulting paper at your request.Since my graation I have been employed by Boston university as an assistant professor. I have continued my research in this time, and several of my papers have been published in New York. my immediate superior, Dr. William Larson, has indicated his willingness to provide my with a reference.I feel that I have sufficient ecation and experience in my background to fulfill the qualifications for your position.

銆銆鍖栧︾殑鑻辨枃鑷鎴戜粙缁嶃绡囥3銆

銆銆Dear ***锛

銆銆I am **** 銆侷 am that a man is brave is *** circle graates銆俆he speciality is measured and maintained锛孏raate from the **** college of auto instry of *****銆

銆銆I study specialized course diligently in the time at school, train one's own self-study ability銆侶ave been admitted to the time at school car steering * and shone锛孯epair the card in automobile intermediate銆侭eing admitted to the automobile sale and after-sale service speciality of undergraate course of self-study examination of the university of Jilin銆

銆銆To always load in Jetta and fields lying fallow in rotation of the treasure of our company one is practised锛孯eceive the leader's trust, with the heavy repair shop of the Audi now銆

銆銆Today, the automobile is fierce in competition , it is higher and higher to people's demand銆侷 like the automobile very much, I like the work of the automobile very much too銆侷 can be competent at the company and hand over any post to me銆侷 is it is it hope leader can give me chance to let me make contribution for company to progress to demand actively銆侺et me offer some strength for beautiful tomorrow of the company锛孍xpress gratitude to the leader's culture銆

D. 用英文介绍下化学元素 AI 就是铝

wiki的解释，按照你的需求，摘录如下
另外，关于你说的发明。。这个是元素，只能发现不能发明啊。。。
理化解释：
Aluminium is a soft, rable, lightweight, ctile and malleable metal with appearance ranging from silvery to ll gray, depending on the surface roughness. Aluminium is nonmagnetic and does not easily ignite.
General useAluminium is the most widely used non-ferrous metal.Global proction of aluminium in 2005 was 31.9 million tonnes. It exceeded that of any other metal except iron (837.5 million tonnes).Forecast for 2012 is 42–45 million tons, driven by rising Chinese output.
应用：
Aluminium is almost always alloyed, which markedly improves its mechanical properties, especially when tempered. For example, the common aluminium foils and beverage cans are alloys of 92% to 99% aluminium.The main alloying agents are copper, zinc, magnesium, manganese, and silicon (e.g., ralumin) and the levels of these other metals are in the range of a few percent by weight.
历史：
Ancient Greeks and Romans used aluminium salts as dyeing mordants and as astringents for dressing wounds; alum is still used as a styptic. In 1761, Guyton de Morveau suggested calling the base alum alumine. In 1808, Humphry Davy identified the existence of a metal base of alum, which he at first termed alumium and later aluminum (see etymology section, below).

E. 化学元素 碳 英文介绍

Carbon is a nonmetallic element, located in the periodic table of the second cycle of IVA family. Latin for Carbonium, meaning "coal, charcoal." Chinese characters "carbon" element of the word from the cyclical nature of charcoal, "carbon" word plus the word next to the stone structure, from the "carbon" pronunciation.
Carbon is a very common element, it is widespread in many forms in the atmosphere and the earth's crust into. Elemental carbon has long been recognized and utilized, a series of carbon compounds - organic matter is essential for life. Carbon is pig iron, wrought iron and steel one of the ingredients. Carbon can be chemically combined to form a large number of self-compounds, biologically and commercially important molecules. Vivo most of the molecules contain carbon [1] element.
Carbon compounds in general obtained from fossil fuels, and then isolated and further synthesized a variety of procts needed for proction and daily life, such as ethylene, plastics and so on.
The existence of many forms of carbon, there are single-crystalline nature of carbon, such as diamond, graphite; whether amorphous carbon such as coal; a complex organic compounds, such as plants and animals, etc.; carbonate, such as marble. One quality of the physical and chemical properties of carbon depends on its crystal structure. High hardness of diamond and soft creamy graphite crystal structure is different, each have their own appearance, density, melting point and so on.
Room temperature, the chemical properties of a single mass of carbon is not lively, not soluble in water, dilute acid, dilute alkali and organic solvents; different reactions under high temperature and oxygen to proce carbon dioxide or carbon monoxide; in halogen only fluoride with a direct response to a single mass of carbon; in the next heat single mass of carbon be easier to acid oxidation; at a high temperature, carbon can also work with many metals the reaction of metal carbides. Carbon has a rective, metal smelting at high temperatures may be.
Chemical symbol: C
Element Atomic Weight: 12.01
Use of proton: 6
Atomic Number: 6
Cycle: 2
Family: IVA
Electron shell distribution :2-4
Atomic volume: 4.58 cubic centimeters / mole
Atomic radius (calculated): 70 (67) pm
Covalent radius: 77 pm
Van der Waals radius: 170 pm
Electron configuration: 1s22s22p2
Electronic energy levels in each row of cloth: 2,4
Oxidation Price (oxide): 4,3,2 (weak acid)
Color and appearance: black (graphite), colorless (diamond)
State of matter: solid-state
Physical Properties: Anti-Magnetic
Melting point: about 3550 ℃ (diamond)
Boiling point: about 4827 ℃ (sublimation)
Molar volume: 5.29 × 10-6m3/mol
The content of elements in the sun: (ppm) 3000
The content of elements in seawater: (ppm) the surface of the Pacific Ocean 23
Content of elements in the Earth's crust: (ppm) 4800
Mohs hardness: 1-2 graphite, diamond 10
Oxidation state: mainly -4,, C +2, C +4 (there are other oxidation state)
Bond can be: (kJ / mol) CH 411 CC 348 C = C 614 C ≡ C 839 C = N 615 C ≡ N 891 C = O 745 C ≡ O 1074
Unit cell parameters: a = 246.4 pm b = 246.4 pm c = 671.1 pm α = 90 ° β = 90 ° γ = 120 °
Ionization energy: (kJ / mol) M - M + 1086.2 M + - M2 + 2352 M2 + - M3 + 4620 M3 + - M4 + 6222 M4 + - M5 + 37827 M5 + - M6 + 47270
Single Quality Density: 3.513 g/cm3 (diamond), 2.260 g/cm3 (graphite, 20 ℃)
Electronegativity: 2.55 (Pauling scale)
Specific heat: 710 J / (kg · K)
Conctivity: 0.061 × 10-6 / (m ohm)
Thermal conctivity: 129 W / (m · K) first ionization energy 1086.5 kJ / mol 2nd ionization energy 2352.6 kJ / mol 3rd ionization energy 4620.5 kJ / mol fourth ionization energy 6222.7 kJ / mol fifth ionization energy 37831 kJ / mol sixth ionization energy 47277.0 kJ / mol
Bond: carbon atoms are generally four price, which requires four single-electron, but the ground state is only two single-electron, it is always carried out when the bonding hybrid. The most common form of hybrid sp3 hybridization, four valence electrons are fully utilized, evenly distributed in the four tracks, the part of other sexual hybrid. Such structures are completely symmetrical, bonding is stable after the σ bonds and no lone electron pairs of exclusion, very stable. Diamond all the carbon atoms they are all for such a hybrid approach in bonding. Alkane carbon atoms are also belong to this category.
According to the needs of sp2 carbon atoms can also be carried out, or sp hybridized. Both methods appear in the re-key into the case, without the hybrid p-orbital perpendicular to the hybrid orbital with the neighboring atom p orbital into the π bond. Alkene double bond connected with the carbon atoms are sp 2 hybridized. Since sp2 hybrid can make atoms coplanar, when there is more than double bond, the molecular plane perpendicular to all the p orbital overlap is likely to form a conjugated system. Benzene is the most typical conjugated system, it has lost some of the nature of the double bond. All the carbon atoms in graphite are in a large conjugation system, each one has a lamellar.
[Edit this paragraph] of carbon isotope
At present a total of 12 kinds of known isotopes, with carbon-8 to C 19, in which the carbon 12 and carbon-13 is stabilized, and the rest are radioactive, which carbon-14 half-lives of over 5000 years, others are less than half full hours. In the Earth's natural world, the carbon 12 content in all accounted for 98.93% of carbon, carbon 13 has 1.07%. C, atomic weight of carbon 12,13 to take two kinds of isotopic abundance-weighted average, the general calculations take 12.01. Carbon 12 is the International System of Units as defined in Moore's standards to contain 12 grams of carbon 12 atoms in a mole number. Carbon-14 has a longer half-life as has been widely used to determine the age of antiquities.
[Edit this paragraph] in the form of elemental carbon
The two most common simple substance is high hardness of diamond and graphite soft and creamy, their crystal structure and bond type are different. Each diamond is tetrahedral four-coordinated carbon, similar to aliphatic compounds; graphite each carbon is a triangle with three bits, can be viewed an unlimited number of benzene rings fused together.
1. Diamond (diamond) Diamond Structure
The most robust of a carbon structure in which the carbon atoms arranged in the form of crystal structure, each carbon atom with the other four carbon atoms tightly bonded, into the spatial network structure, and ultimately form a kind of hardness, poor activity solids.
Chao Guo diamond melting point of 3500 ℃, the equivalent of some stellar surface temperature.
Main function: decoration, cutting metal materials
2. Graphite (graphite)
Graphite is a dark gray metallic luster and opaque sweetlips flaky solid. Soft, with creamy feel, with excellent electrical properties. Graphite planar layered structure of carbon atoms bonded together, bonding layer and the layer of saw relatively weak, so between layers are separated easily be sliding.
A major role: proction of pencils, electrodes, cables and so on tram
3. Fullerene (fullerene, C60, C72, etc.)
In 1985 by the U.S. Ross University of Texas scientists have discovered.
Fullerene carbon atoms are spherical dome structure of bond together.
4. Other carbon structures
Hexagonal diamond (Lonsdaleite, and diamond have the same bond type, but the hexagonal arrangement of atoms, also known as hexagonal diamond)
Graphene (graphene, ie single-layer graphite)
Carbon nanotubes (Carbon nanotube, it has the typical structural features of layered hollow)
Monoclinic super-hard carbon (M-carbon, graphite, after low-temperature high-pressure phase, with monoclinic structure, and its hardness close to diamond)
Amorphous carbon (Amorphous, not really shaped body, the internal structure of graphite)
Zhao graphite (Chaoite, graphite and meteorite collision, in an hexagonal pattern of the atomic arrangement)
Mercury tetrahedrite ore structure (Schwarzite, e to the emergence of heptagonal, hexagonal layers are distorted to the "negative curvature," saddle-shaped in the hypothetical structure)
Carbon fiber (Filamentous carbon, growing chain of small piece of the heap formed by fibers)
Carbon aerogels (Carbon aerogels, the density of the porous structure of very small, similar to the well-known silicon aerogels)
Carbon nano-foam (Carbon nanofoam, cobweb-like banding-shaped structure, density is one per cent of the carbon aerogels, there is ferromagnetism)
Hexagonal diamond single graphite and carbon nanotubes monoclinic super-hard carbon (M-carbon)
[Edit this paragraph] carbon compounds
Carbon compounds, only the following compounds are inorganic substances:
Of carbon oxides, sulfur: carbon monoxide (CO), carbon dioxide (CO2), carbon disulfide (CS2), carbonate, bicarbonate salts, cyanide and its intended range of halogen-halide intended to be halide salts: cyanide (CN) 2, oxygen-cyanide, sulfur, cyanide.
Other carbon-containing compounds are organic compounds. As the carbon atoms to form the keys are relatively stable, the number of organic compounds of carbon, arranged, as well as the type of substituent, position, have a high degree of randomness, resulting in an extremely diverse amount of organic matter in this phenomenon, the present compounds found in human beings accounted for the vast majority of organic matter.
Organic and inorganic very different nature, they are generally flammable, easily soluble in water, the reaction mechanism is very complex, has been the formation of a separate Division - Organic Chemistry. Distribution of carbon found in nature (as in the form of diamond and graphite), is coal, oil, asphalt, limestone and other carbonates, as well as the most important ingredient of all organic compounds in the crust of the content was about 0.027%. Carbon is the dry weight of organisms accounted for the largest proportion of an element. Carbon is also in the form of carbon dioxide in the atmosphere circle the planet and stratosphere. In most of the objects and the presence of carbon in the atmosphere are.
[Edit this paragraph] of carbon found in the history of
Diamond and graphite have known prehistoric humans.
Fullerenes were found in 1985, has since found a number of different arrangement of carbon simple substance.
Isotope carbon-14 by United States scientists Martinka doors and Samuel Rubin was discovered in 1940.
Hexagonal diamond by United States scientists Galiffo Derong Deere and Yousulama temperature was found in 1967.
Monoclinic super-hard carbon scientists from the United States in 1967, Bondi and Cuthbert was found that its crystal structure from Jilin University, Dr. Li Quan and mentor Professor Ma Yanming theory established in 2009.

F. 用英文介绍自己的化学学习情况

用英文介绍自己的化学学习情况
参考
I am a hard-working girl.I am very good at several subjects such as maths,physics and history.But my chemistry is not good because she finds it boring. I also wants to learn chemistry well,and with the help of the teacher,I will study it much harder in order that I can make great progress.

G. 化学元素周期表图规律特点，用英文叙述

The periodic law is most commonly expressed in chemistry in the form of a periodic table, or chart. The so-called short-form periodic table, based on Mendeleyev's table, with subsequent emendations and additions, is still in widespread use. In this table the elements are arranged in seven horizontal rows, called the periods, in order of increasing atomic weights, and in 18 vertical columns, called the groups. The first period, containing two elements, hydrogen and helium, and the next two periods, each containing eight elements, are called the short periods. The remaining periods, called the long periods, contain 18 elements, as in periods 4 and 5, or 32 elements, as in period 6. The long period 7 includes the actinide series, which has been filled in by the synthesis of radioactive nuclei through element 102, nobelium. Heavier transuranium elements have also been synthesized.

The groups or vertical columns of the periodic table have traditionally been labeled from left to right using Roman numerals followed by the symbol a or b, the b referring to groups of transition elements. Another labeling scheme, which has been adopted by the International Union of Pure and Applied Chemistry (IUPAC), is gaining in popularity. This new system simply numbers the groups sequentially from 1 to 18 across the periodic table.

All the elements within a single group bear a considerable familial resemblance to one another and, in general, differ markedly from elements in other groups. For example, the elements of group 1 (or Ia), with the exception of hydrogen, are metals with chemical valence of +1; while those of group 17 (or VIIa), with the exception of astatine, are nonmetals, commonly forming compounds in which they have valences of -1.

In the periodic classification, noble gases, which in most cases are unreactive (valence = 0), are interposed between highly reactive metals that form compounds in which their valence is +1 on one side and highly reactive nonmetals forming compounds in which their valence is -1 on the other side. This phenomenon led to the theory that the periodicity of properties results from the arrangement of electrons in shells about the atomic nucleus. According to the same theory, the noble gases are normally inert because their electron shells are completely filled; other elements, therefore, may have some shells that are only partly filled, and their chemical reactivities involve the electrons in these incomplete shells. Thus, all the elements that occupy a position in the table preceding that of an inert gas have one electron less than the number necessary for completed shells and show a valence of -1, corresponding to the gain of one electron in reactions. Elements in the group following the inert gases in the table have one electron in excess of the completed shell structure and in reactions can lose that electron, thereby showing a valence of + 1.

An analysis of the periodic table, based on this theory, indicates that the first electron shell may contain a maximum of 2 electrons, the second builds up to a maximum of 8, the third to 18, and so on. The total number of elements in any one period corresponds to the number of electrons required to achieve a stable configuration. The distinction between the a and b subgroups of a given group also may be explained on the basis of the electron shell theory. Both subgroups have the same degree of incompleteness in the outermost shell but differ from each other with respect to the structures of the underlying shells. This model of the atom still provides a good explanation of chemical bonding.

There are 18 vertical columns, or groups, in the standard periodic table. At present, there are three versions of the periodic table, each with its own unique column headings, in wide use. The three formats are the old International Union of Pure and Applied Chemistry (IUPAC) table, the Chemical Abstract Service (CAS) table, and the new IUPAC table. The old IUPAC system labeled columns with Roman numerals followed by either the letter A or B. Columns 1 through 7 were numbered IA through VIIA, columns 8 through 10 were labeled VIIIA, columns 11 through 17 were numbered IB through VIIB and column 18 was numbered VIII. The CAS system also used Roman numerals followed by an A or B. This method, however, labeled columns 1 and 2 as IA and IIA, columns 3 through 7 as IIIB through VIB, column 8 through 10 as VIII, columns 11 and 12 as IB and IIB and columns 13 through 18 as IIIA through VIIIA. However, in the old IUPAC system the letters A and B were designated to the left and right part of the table, while in the CAS system the letters A and B were designated to the main group elements and transition elements respectively. (The preparer of the table arbitrarily could use either an upper-or lower-case letter A or B, adding to the confusion.) Further, the old IUPAC system was more frequently used in Europe while the CAS system was most common in America. In the new IUPAC system, columns are numbered with Arabic numerals from 1 to 18. These group numbers correspond to the number of s, p, and d orbital electrons added since the last noble gas element (in column 18). This is in keeping with current interpretations of the periodic law which holds that the elements in a group have similar configurations of the outermost electron shells of their atoms. Since most chemical properties result from outer electron interactions, this tends to explain why elements in the same group exhibit similar physical and chemical properties. Unfortunately, the system fails for the elements in the first 3 periods (or rows; see below). For example, aluminum, in the column numbered 13, has only 3 s, p, and d orbital electrons. Nevertheless, the American Chemical Society has adopted the new IUPAC system.

The horizontal rows of the table are called periods. The elements of a period are characterized by the fact that they have the same number of electron shells; the number of electrons in these shells, which equals the element's atomic number, increases from left to right within each period. In each period the lighter metals appear on the left, the heavier metals in the center, and the nonmetals on the right. Elements on the borderline between metals and nonmetals are called metalloids.

Group 1 (with one valence electron) and Group 2 (with two valence electrons) are called the alkali metals and the alkaline-earth metals, respectively. Two series of elements branch off from Group 3, which contains the transition elements, or transition metals; elements 57 to 71 are called the lanthanide series, or rare earths, and elements 89 to 103 are called the actinide series, or radioactive rare earths; a third set, the superactinide series (elements 122–), is predicted to fall outside the main body of the table, but none of these has yet been synthesized or isolated. The nonmetals in Group 17 (with seven valence electrons) are called the halogens. The elements grouped in the final column (Group 18) have no valence electrons and are called the inert gases, or noble gases, because they react chemically only with extreme difficulty.

In a relatively simple type of periodic table, each position gives the name and chemical symbol for the element assigned to that position; its atomic number; its atomic weight (the weighted average of the masses of its stable isotopes, based on a scale in which carbon-12 has a mass of 12); and its electron configuration, i.e., the distribution of its electrons by shells. The only exceptions are the positions of elements 103 through 118; complete information on these elements has not been compiled. Larger and more complicated periodic tables may also include the following information for each element: atomic diameter or radius; common valence numbers or oxidation states; melting point; boiling point; density; specific heat; Young's molus; the quantum states of its valence electrons; type of crystal form; stable and radioactive isotopes; and type of magnetism exhibited by the element (paramagnetism or diamagnetism).

The layout of the periodic table demonstrates recurring ("periodic") chemical properties. Elements are listed in order of increasing atomic number (i.e., the number of protons in the atomic nucleus). Rows are arranged so that elements with similar properties fall into the same columns (groups or families). According to quantum mechanical theories of electron configuration within atoms, each row (period) in the table corresponded to the filling of a quantum shell of electrons. There are progressively longer periods further down the table, grouping the elements into s-, p-, d- and f-blocks to reflect their electron configuration.

In printed tables, each element is usually listed with its element symbol and atomic number; many versions of the table also list the element's atomic mass and other information, such as its abbreviated electron configuration, electronegativity and most common valence numbers.

As of 2006, the table contains 117 chemical elements whose discoveries have been confirmed. Ninety-four are found naturally on Earth, and the rest are synthetic elements that have been proced artificially in particle accelerators. Elements 43 (technetium), 61 (promethium) and all elements greater than 83 (bismuth), beginning with 84 (polonium) have no stable isotopes. The atomic mass of each of these element's isotope having the longest half-life is typically reported on periodic tables with parentheses.[1] Isotopes of elements 43, 61, 93 (neptunium) and 94 (plutonium), first discovered synthetically, have since been discovered in trace amounts on Earth as procts of natural radioactive decay processes.

The primary determinant of an element's chemical properties is its electron configuration, particularly the valence shell electrons. For instance, any atoms with four valence electrons occupying p orbitals will exhibit some similarity. The type of orbital in which the atom's outermost electrons reside determines the "block" to which it belongs. The number of valence shell electrons determines the family, or group, to which the element belongs.

The total number of electron shells an atom has determines the period to which it belongs. Each shell is divided into different subshells, which as atomic number increases are filled in roughly this order (the Aufbau principle):

Groups
Main article: Group (periodic table)
A group or family is a vertical column in the periodic table. Groups are considered the most important method of classifying the elements. In some groups, the elements have very similar properties and exhibit a clear trend in properties down the group. These groups tend to be given trivial (unsystematic) names, e.g., the alkali metals, alkaline earth metals, halogens, pnictogens, chalcogens, and noble gases. Some other groups in the periodic table display fewer similarities and/or vertical trends (for example Group 14), and these have no trivial names and are referred to simply by their group numbers.

Periods
Main article: Period (periodic table)
A period is a horizontal row in the periodic table. Although groups are the most common way of classifying elements, there are some regions of the periodic table where the horizontal trends and similarities in properties are more significant than vertical group trends. This can be true in the d-block (or "transition metals"), and especially for the f-block, where the lanthanoids and actinoids form two substantial horizontal series of elements.

Blocks
Main article: Periodic table block
This diagram shows the periodic table blocks.Because of the importance of the outermost shell, the different regions of the periodic table are sometimes referred to as periodic table blocks, named according to the subshell in which the "last" electron resides. The s-block comprises the first two groups (alkali metals and alkaline earth metals) as well as hydrogen and helium. The p-block comprises the last six groups (groups 13 through 18) and contains, among others, all of the semimetals. The d-block comprises groups 3 through 12 and contains all of the transition metals. The f-block, usually offset below the rest of the periodic table, comprises the rare earth metals.

Other
The chemical elements are also grouped together in other ways. Some of these groupings are often illustrated on the periodic table, such as transition metals, poor metals, and metalloids. Other informal groupings exist, such as the platinum group and the noble metals.

Periodicity of chemical properties
The main value of the periodic table is the ability to predict the chemical properties of an element based on its location on the table. It should be noted that the properties vary differently when moving vertically along the columns of the table than when moving horizontally along the rows.

Periodic trends of groups
Modern quantum mechanical theories of atomic structure explain group trends by proposing that elements within the same group have the same electron configurations in their valence shell, which is the most important factor in accounting for their similar properties. Elements in the same group also show patterns in their atomic radius, ionization energy, and electronegativity. From top to bottom in a group, the atomic radii of the elements increase. Since there are more filled energy levels, valence electrons are found farther from the nucleus. From the top, each successive element has a lower ionization energy because it is easier to remove an electron since the atoms are less tightly bound. Similarly, a group will also see a top to bottom decrease in electronegativity e to an increasing distance between valence electrons and the nucleus.

Periodic trends of periods
Periodic trend for ionization energy. Each period begins at a minimum for the alkali metals, and ends at a maximum for the noble gases.Elements in the same period show trends in atomic radius, ionization energy, electron affinity, and electronegativity. Moving left to right across a period, atomic radius usually decreases. This occurs because each successive element has an added proton and electron which causes the electron to be drawn closer to the nucleus. This decrease in atomic radius also causes the ionization energy to increase when moving from left to right across a period. The more tightly bound an element is, the more energy is required to remove an electron. Similarly, electronegativity will increase in the same manner as ionization energy because of the amount of pull that is exerted on the electrons by the nucleus. Electron affinity also shows a slight trend across a period. Metals (left side of a period) generally have a lower electron affinity than nonmetals (right side of a period) with the exception of the noble gases.