At sea level, ozone in the atmosphere is a pollutant, produced by the action of sunlight on nitrogen oxides in car exhaust. In the stratosphere, at an elevation of 10 to 50 km about the surface of the Earth, ozone is produced by the action of sunlight upon O 2 , which splits apart into atomic oxygen, O, and combines with another O 2 molecule to form ozone, O 3.
The ozone absorbs high-energy ultraviolet light, splitting apart into O 2 and O, which can then recombine and absorb another photon of high-energy light. This ozone layer forms a shield which protects living organisms on the Earth's surface from this damaging, high-energy light.
The release of CFCs chlorofluorocarbons into the atmosphere produces chlorine radicals which are damaging to the ozone layer; for this reason, these substances are being phased out. See the Molecules pages on dichlorodifluoromethane for more information. This is unusual for the solid form of a liquid substance, and one reason why if you're sailing in a ship in the North Atlantic, it's a good idea to keep a lookout for icebergs.
These "anomalous" properties of water are in part a 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 other small molecules do, as a results of these hydrogen bonds.
See the entry on hydrogen for more on hydrogen bonds. Sulfur is a yellow nonmetal, and is found in a variety of forms, ranging from a yellow powder to more crystalline structures. The name is derived from the ancient names for the element, either the Sanskrit word sulvere , the Latin word sulfurium , or the Arabic word sufra.
It is found in the Earth's crust at a concentration of 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.
Sulfur has been known in its elemental form since ancient times often under the name "brimstone". It is a yellow nonmetal, and is found in a number of allotropic forms, including orthorhombic sulfur, monoclinic sulfur, etc. It forms rings containing anywhere from 4 to 20 atoms of sulfur; S 8 is the most common form.
When heated to high temperatures, these rings break open, and join to form long chains; the resulting material is extremely viscous, and forms a rubbery solid called "plastic sulfur.
Sulfur is present in proteins, in the form of the amino acids cysteine and methionine; on average milligrams of sulfur are consumed every day in this manner. Probably the most important compound of sulfur is sulfuric acid, H 2 SO 4 , which is the industrial chemical produced in the largest amounts million tons in Sulfuric acid is used in the production of phosphates for fertilizers, the removal of rust from iron, the production of explosives, paints, paper, detergents, dyes, in lead-acid car batteries, and many other uses.
Sulfuric acid has a high affinity for water, and is used as a dehydrating agent. This can be easily demonstrated: applying concentrated sulfuric acid to paper causes the paper to become black and charred, as if it had been burned; sulfuric acid also removes water from sugar, leaving behind a solid mass of carbon. A common laboratory mistake is to mix sulfuric acid and water by adding water to the concentrated sulfuric acid: the mixing of sulfuric acid and water can produce enough heat to boil the water, splattering the water and acid all over the incautious chemist.
It is a standing rule in all chemistry labs that, when diluting acids, always add the acid to the water, never the water to the acid. Since sulfur is found in two amino acids cysteine and methionine , some sulfur is present in fossil fuels such as coal. When the coal is burned, the sulfur is oxidized to form sulfur dioxide, SO 2 , and sulfur trioxide, SO 3 ; these gases react with moisture in the air, producing sulfurous acid, H 2 SO 3 , and sulfuric acid, H 2 SO 4 , respectively.
This leads to the formation of acid rain, which is a serious environmental pollutant in some areas. Many compounds containing sulfur are bad news for the nose. Hydrogen sulfide, H 2 S, is produced during the breakdown of organic matter by bacteria in the absence of oxygen; it is found is swamps, natural gas, volcanic gases, and many other sources. It is detectable by humans at concentrations of 4.
Organic compounds containing sulfur are called thiols also known as mercaptans for their ability to encapsulate mercury ; thiols are responsible for the odor of skunks , the odor of cut onions and garlic, the smell of natural gas which comes from ethanethiol, CH 3 CH 2 SH, which added to natural gas to make gas leaks detectable , bad breath halitosis , and other similar odors.
Gunpowder was first made in China in about the year It is composed of charcoal, sulfur, and potassium nitrate. This mixture also comes in handy if you're being chased by a Gorn. If you have to ask, you probably don't want to know. The first message is that it is time to consider the old definitions as purely historical.
Chemistry has gotten very complex over the last 50 years and the textbook authors have to simplify, but the classical definitions of elements and compounds are too out-of-date for what we now know about chemistry.
Above all, the designation of element should be reserved for the atoms themselves, and for the common forms of the elements, the designation of elementary substances should be used. For the designation as compounds it is not clear what most authors will do. One approach is just to forget the historical definition and follow the approach given by IUPAC, but for some teachers schooled in the old ways that might be too much.
We know that all molecules are unique, held together by the same kinds of chemical bonds regardless of whether the nuclei are identical or not. As a compromise, we offer the following designations: chemical substances and elementary substances. Chemical substances are compounds if they have formula weights that are not simply atomic weights. It seems logical that all molecules should be called compounds.
This would mean that dinitrogen, ozone, and C 60 , which have their unique formula weights, could be called compounds, but metallic gold or graphite, which have no unique formula weight, should be called elementary substances.
At the same time, some authors might be more radical and say that all substances held together by chemical bonds are compounds. We could even invent the term elementary compound, but that would seem to be unnecessary.
We should also give up the idea that chemistry is devoted entirely to making pure compounds. Many of the most important substances these days are prepared not to be pure and can be called materials or doped compounds.
View Author Information. Cite this: J. Article Views Altmetric -. Citations 3. Abstract The definitions of elements and compounds have changed very little in the past years, but chemistry itself has changed a great deal over time.
Author Information. Rollie J. Chemical Principles ; W. Freeman : New York , ; p, B10 , F Google Scholar There is no corresponding record for this reference. Kluwer Academic Publishers. This article tries to present the epistemol. To make communication possible it is necessary to use certain tech. Since the concern is with the discussion of a particular problem pertaining to science - which must retain its meaning for every epistemol. For reasons of expediency the article mainly follows the terminol.
The question whether Hartmann's "transcendental realism" in some points even depended too much on the science of his time can be ignored here, just as we can, for our purpose, completely ignore his metaphys. College Chemistry ; W. In eminent chemist Fritz Paneth maintained that the modern notion of "element" is closely related to and as "metaphys. On that basis, the element chlorine properly so-called is not the elementary substance dichlorine, but rather chlorine as it is in carbon tetrachloride.
The fact that pure chems. When the main features of the constitution of isotopes became clear in the first half of the twentieth century, the formal IUPAC definition of a "chem. The features that are "essential" to being an element had previously been "transcendental" "beyond the sphere of consciousness" but, by the mid-twentieth century the defining characteristics of elements, as such, had come to be understood in detail.
This amts. It is not easy to split up a compound into its elements - the only way to do this is in chemical reactions. Chemical formulae of compounds A compound is a substance that contains two or more elements that are chemically combined.
The formula shows: the symbols for each element in the compound the number of atoms of each element in a unit of the compound For example, magnesium oxide is made up of two elements, magnesium and oxygen. In compounds made up of non-metal elements only, the second word of the compound's name starts with mon-, di-, or tri-, eg carbon dioxide. This shows the number of atoms of this element for every one atom of the first element in the name.
So for carbon dioxide there are two oxygen atoms for every carbon atom. Sodium chloride. Potassium bromide. Magnesium iodide.
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