Group 6A(oTHROUGH THE) of the periodic table are thechalcogens: the nonmetals oxygen (O), sulfur (S) and selenium (Se), the metalloid tellurium (Te) and the metal polonium (Po). The name "chalcogen" means "ancient mineral", derived from the Greek wordswedges("mineral") y-gen("formation").
Elements in group 6A have six valence electrons in their highest energy orbitals (ns2public notary4🇧🇷 This is only two electrons away from having a full octet of eight electrons, so many of these elements form anions with -2 charges: oxide, O2-🇬🇧 sulfur, S2-, seleneto, se2-, etc. In combination with other nonmetals, oxygen, sulfur, and selenium form compounds through covalent bonds.
Oxygen is a colorless, odorless, tasteless and extremely reactive gas; in its elemental form, oxygen is found as the diatomic molecule O2🇧🇷 in the liquid phase, it is pale blue. The name of the element is derived from the Latin wordsoximigenes, which means "acid formation" (see explanation below). Oxygen is the most abundant element in the Earth's crust (47%), the second most abundant element in the atmosphere (21%), and the third most abundant element in the universe (for every silicon atom there are 22 oxygen atoms, 3,100 of helium atoms and 40,000 of hydrogen).
Oxygen forms compounds with all other elements except the lightest noble gases. It is found in many minerals, in the form of oxides (O2-), sulfates (SO42-), nitrates (NO3-), phosphates (PO43-), carbonates (CO32-), silica and quartz (SiO2) and silicates, etc. In the atmosphere it is found in its elemental form, which is a diatomic molecule, O2, formed by two oxygen atoms joined by a double bond. (Actually, the link O2is a bit more complicated than that, because the second pair of electrons in the "double bond" is unpaired.) When cooled to a temperature of -183ºC, oxygen forms a light blue liquid, which is attracted to the poles of a very strong magnet.
Oxygen is essential for breathing; Molecular oxygen collected in the lungs is used to oxidize sugar molecules, resulting in the production of carbon dioxide, water, and lots of energy. Photosynthesis in plants reverses this process; green plants and photosynthetic bacteria absorb carbon dioxide and use energy from sunlight to convert it into sugar molecules, releasing oxygen in the process. Molecular oxygen was first released into the atmosphere by primitive photosynthetic bacteria about 3.5 to 3.8 billion years ago; when land plants evolved, the concentration of O2in the atmosphere has risen to about 20%. Oxygen dissolves in water at the rate of 1.2 milligrams per liter of water; that's not much, but it's essential for aquatic life.(Video) Parts of the Periodic Table
Burning fuels in the presence of molecular oxygen is where we get most of our electricity and how we power cars. Petroleum hydrocarbons and their refined products, such as natural gas, gasoline, and diesel, are burned with oxygen to produce carbon dioxide, water, and lots of energy. Burning coal to produce carbon dioxide also produces energy.
The complete combustion of hydrocarbons produces carbon dioxide; if there is not enough oxygen, carbon monoxide or elemental carbon can be produced. (The yellow-orange color of burned wood comes from hot elemental carbon that forms because solid fuel doesn't mix well with gaseous oxygen.)See AlsoFinCEN Currency Transaction Report (CTR) FAQHistory of 10 Downing StreetCode of Conduct for US JudgesNational Archives - Home Page
Things are more flammable in pure oxygen than in the 21% oxygen of the normal atmosphere (seeherefor demonstration). Even iron, which does not burn at 21% oxygen, burns at 100% oxygen (seehere🇧🇷 This led to disaster in the early days of the American space program. The capsules used in the Mercury, Gemini, and Apollo programs operated in space with an atmosphere of pure oxygen at a pressure of 5 psi. (Normal atmospheric pressure is approximately 14.7 psi. The reduced pressure oxygen environment was used to eliminate the need to carry nitrogen tanks into space for astronauts to breathe, in the belief that the components of a system two-gas would be more difficult to handle, as it would require the oxygen/nitrogen ratio to be precisely calibrated at all times to prevent asphyxiation of the astronauts). Since the spacecraft was supposed to operate in a pure oxygen environment in space, they were tested on the ground in a pure oxygen environment. There were no complications with these tests during the Mercury and Gemini programs of the early 1960s, but on January 27, 1967, a fire broke out during a routine test in the command module of what would become the first mission. of the spaceship.ApolloProgram; the door swung inwards and quickly became impossible to open against the pressure of the gases generated in the fire. Within 17 seconds, astronauts Virgil Grissom, Ed White, and Roger Chaffee were dead. As a result of the disaster, the command module was extensively redesigned to prevent such a tragedy from ever happening again.
Oxygen is used in welding to generate the intense heat needed to cut and weld steel and other high-melting metals. It is used in hospitals to provide oxygen to patients who have difficulty breathing. Also used as rocket fuel: the Saturn V rockets that launched theApolloLunar missions used 209,000 gallons of kerosene and 334,500 gallons of liquid oxygen in their first stage (S-IC), and 260,000 gallons of liquid hydrogen and 83,000 gallons of liquid oxygen in their second stage (S-II) and 69,500 gallons of hydrogen liquid and 20,150 gallons of liquid oxygen in its third stage (S-IVB); The space shuttle main engines use 385,000 gallons of liquid hydrogen and 143,000 gallons of liquid oxygen.
The discovery of oxygen is an extremely confusing story, partly due to issues of priority and partly due to misunderstandings about the nature of combustion and the gas phase. For thousands of years, air was considered an "element" and it was not recognized that air was actually a mixture of many different gases. The nature of combustion has also been hotly debated (pun intended); many scientists believed that flammable substances contained a material calledphlogiston, which was released when a substance was burned. When nitrogen was discovered in 1772, it was called "phlogiston air" since an atmosphere of pure nitrogen (actually nitrogen plus carbon dioxide) did not support combustion. (This "air" was thought to have absorbed the greatest amount of phlogiston.) Swedish chemist Carl Wilhelm Scheele discovered oxygen in 1772, but the account of his experiment was not published until 1777. English chemist Joseph Priestley produced oxygen in 1774. , heating a sample of mercury(II) oxide, HgO, and collecting the gaseous oxygen produced in the water. He called the gas "dephlogisticated air" since it supported combustion more vigorously than "normal" air and was therefore presumably able to better "pull" phlogiston out of other substances. The French chemist Antoine Lavoisier claimed to have produced oxygen in 1774 independently of Priestley, but Priestley visited him a few months earlier and told him about his experiment. Lavoisier, however, correctly interpreted the meaning of Priestley's result: that combustion is not the release of phlogiston from a substance, but the combination of the substance with oxygen from the air, to produce oxides (as well as heat and light). Lavoisier believed that the new element was an essential component of all acids and proposed that it be called "oxygen", from the Greek wordsoxi, "acid" andgenes"forming". (However, not all acids contain oxygen; for example, hydrochloric acid, HCl.)
Another well-known form of oxygen isozone, of3🇧🇷 Ozone is a powerful oxidizing agent and is often used to kill bacteria during water purification. At sea level, ozone in the atmosphere is a pollutant, produced by the action of sunlight on nitrogen oxides from automobile exhaust gases. In the stratosphere, at an altitude of 10 to 50 km above the earth's surface, ozone is produced by the action of sunlight on O2, which splits into atomic oxygen, O, and combines with another O2molecule to form ozone, O3🇧🇷 Ozone absorbs high-energy ultraviolet light and splits into O2and O, which can recombine and absorb another high-energy photon of light. Eastozone layerit forms a shield that protects living organisms on the Earth's surface from this harmful high-energy light. The release of CFCs (chlorofluorocarbons) into the atmosphere produces chlorine radicals that damage the ozone layer; for this reason, these substances are being phased out. (See the Molecules pages ondichlorodifluoromethaneFor more information.)(Video) Parts of the Periodic Table
One of the most important compounds of oxygen isagua, h2Or, which makes up almost 75% of the Earth's surface. The water freezes at 0ºC to form solid ice, which is less dense than liquid water. (This is unusual for the solid form of a liquid substance, and one of the reasons why, if you're sailing a ship in the North Atlantic, it's a good idea to watch out for icebergs.) Water boils at 100°C. .ºC, which is again uncommon; most low molecular weight compounds (water weighs 18.02 g/mol) are gases at room temperature. These "anomalous" properties of water are, in part, the result of the large differences in electronegativity between oxygen and hydrogen: the oxygen-hydrogen bond is extremely polar, and water molecules attract each other much more strongly than most small molecules. . results of these hydrogen bonds. (See entry inhydrogento learn more about hydrogen bonding.)
Sulfur is a yellow nonmetal and occurs in a variety of forms, ranging from a yellow powder to more crystalline structures. The name is derived from the ancient names of the element, either the Sanskrit wordspeak, the Latin wordsulfurio, or the arabic wordMesa🇧🇷 It is found in the earth's crust at a concentration of 260 ppm, making it the 17th most abundant element. Sulfur can be mined in its elemental form near volcanoes and hot springs, and is mined from salt domes along the Gulf of Mexico, Poland, and Russia (where it was produced by the action of bacteria on sulfate-containing minerals). It is also present in many minerals such as stibnite [antimony sulfide, Sb2S3], galena [lead(II) sulfide, PbS], cinnabar [mercury(II) sulfide, HgS], sphalerite [zinc sulfide, ZnS], pyrite [iron(II) sulfide, FeS], anhydrite, and gypsum [calcium sulfate, CaSO4], epsomite [magnesium sulfate, MgSO4], alunite [potassium and aluminum sulphate, KAl(SO4)2] and barite [barium sulfate, BaSO4], among others.
Sulfur has been known in its elemental form since ancient times (often under the name "brimstone"). It is a yellow nonmetal and occurs in various allotropic forms including orthorhombic sulfur, monoclinic sulfur, etc. It forms rings containing from 4 to 20 sulfur atoms; yes8Is the most usual way. When heated to high temperatures, these rings split open and join together to form long chains; the resulting material is extremely viscous and forms a rubbery solid called "plastic sulfur". Sulfur is used in the manufacture of sulfuric acid, in the manufacture of vulcanized rubber, in gunpowder and fireworks, etc. Sulfur is present in proteins in the form of the amino acids cysteine and methionine; on average, 900 milligrams of sulfur are consumed daily in this way.
Probably the most important sulfur compound is sulfuric acid, H2SO4, which is the most produced industrial chemical (165 million tons in 2001). Sulfuric acid is used to make phosphates for fertilizers, remove rust from iron, make explosives, paints, paper, detergents, dyes, lead-acid batteries for automobiles, and many other uses. Sulfuric acid has a high affinity for water and is used as a dehydrating agent. This can be easily demonstrated: the application of concentrated sulfuric acid to paper causes the paper to turn black and charred, as if it had been burned; sulfuric acid also removes water from sugar, leaving a solid mass of carbon. A common laboratory error is to mix sulfuric acid and water by adding water.byConcentrated Sulfuric Acid: Mixing sulfuric acid and water can produce enough heat to boil the water, spreading the water and acid all over the unsuspecting chemist. It is a permanent rule in all chemistry laboratories that when diluting acids,always add acid to water, never water to acid.
Since sulfur is found in two amino acids (cysteine and methionine), some sulfur is present in fossil fuels such as coal. When coal is burned, sulfur is oxidized to form sulfur dioxide, SO2and sulfur trioxide, SO3🇧🇷 these gases react with the humidity of the air, producing sulfuric acid, H2SO3, and sulfuric acid, H2SO4, respectively. This leads to the formation of acid rain, which is a serious environmental pollutant in some areas.(Video) The periodic table - classification of elements | Chemistry | Khan Academy
Many sulfur-containing compounds are bad news for the nose. hydrogen sulfide, H2S, is produced during the decomposition of organic matter by bacteria in the absence of oxygen; It is found in swamps, natural gas, volcanic gases, and many other sources. It is detectable by humans at concentrations of 4.7 parts per billion or higher, and it smells like rotten eggs. Organic sulfur-containing compounds are called thiols (also known as mercaptans for their ability to encapsulate mercury); Thiols are responsible for the odor ofzarigueyas, the smell of chopped onion and garlic, the smell of natural gas (which comes from ethanethiol, CH3CH2SH, which is added to natural gas to detect gas leaks), bad breath (halitosis), and other similar odors.
Gunpowder was first made in China around the year 950. It is composed of charcoal, sulfur, and potassium nitrate. (This mixture is also useful if you are being chased by aHorn🇧🇷 If you have to ask, you probably don't want to know.) Sulfur was probably also present in Greek fire, along with tar and antimony sulfide (see entry forantimony🇧🇷 It is also present in mustard gas and other poisonous gases and nerve agents.
Selenium is a soft metalloid found in various allotropic forms. The element's name is derived from the Greek word for moon,selene, as tellurium got its name from Earth. It is found in the earth's crust at a concentration of 50 ppb, making it the 67th most abundant element. Selenium minerals are rare and usually found as selenide (Se2-) together with sulfide (S2-) in ores of copper, lead, zinc and other metals.
Selenium conducts electricity much better in the presence of light than in the dark; for this reason, it is used in photoelectric cells, camera light meters, solar cells, copiers, and other light-sensitive devices. Selenium is essential in the diet in small amounts, but levels greater than 5 mg can be toxic. High levels of selenium in the body can cause bad breath and body odor as a result of the production of volatile dimethylselenide (CH3)2Se.
In areas where the soil is particularly rich in selenium (such as the Great Plains in the central United States), there are some plants that are particularly efficient at extracting selenium from the soil. These plants include Milkvetch (genusAstragalus) and various species of the genusoxitropis🇧🇷 When cattle eat these plants, they develop some of the symptoms of selenium poisoning, including erratic behavior, aggressiveness, nervousness, lethargy, and loss of balance ("blind wobble"). These plants are often called "hierba loca" (from the Spanish wordLoca, "Loca").(Video) The Periodic Table Song (2018 Update!) | SCIENCE SONGS
Tellurium is a metalloid; it has a characteristic metallic luster, but can be pulverized to form a gray powder. The element name is derived from the Latin word for Earth,tierra🇧🇷 It is found in the earth's crust at a concentration of 5 ppb, making it the 72nd most abundant element. Found in calaverite and krennerite ores [gold telluride, AuTe2], sylvanite [silver and gold telluride, (Ag,Au)Te2], petzite [Ag3AuTe2] and tellurite [TeO2], although it is normally obtained as a by-product of copper and lead refining.
Tellurium is used to make alloys with stainless steel and copper to increase their machinability, and is sometimes used to vulcanize rubber. It is also used in detonators. Exposure to tellurium can cause bad breath and body odor as a result of the production of volatile dimethyltelluride (CH3)2o
Polonium is a silvery radioactive metal discovered by Marie Curie in 1898 (along with radium); she named the element after Poland, her native country. Although the discovery of polonium was eclipsed to some extent by the discovery of radium, polonium is more radioactive than radium by a factor of about 5,000. It occurs naturally in uranium ore in extremely small amounts; one ton of uranium ore contains about 100 micrograms (0.0001 g) of polonium, making it one of the ten least abundant natural elements. For industrial use (mainly to dissipate static electricity), it is produced by irradiating bismuth-209 with neutrons to produce bismuth-210, which undergoes beta decay to produce polonium-210. It is radioactive and is considered one of the deadliest substances known. Polonium is produced in the radioactive decay of radon gas; When radon is inhaled, it can undergo alpha decay to produce polonium, which is a solid and is trapped within the lungs.
John Emsley,The elements, 3rd edition. Oxford: Clarendon Press, 1998.(Video) Periodic Table Explained: Introduction
John Emsley,Building Blocks of Nature: An A to Z Guide to the Elements. Oxford: Oxford University Press, 2001.
David L Heiserman,Exploring the chemical elements and their compounds. New York: TAB Books, 1992.
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