Encyclopedia about Chemistry

Inorganic carbon compounds

Inorganic macromolecule carbon-containing compounds are either found in nature or made synthetically. In the production of inorganic macromolecules, elements such as carbon or the compounds of silicon oxide and silicon-containing acids are bonded together to form polymers. Diamond, graphite and quartz are among the inorganic micromolecules found in nature which contain carbon. Diamond and graphite are composed of carbon atoms which are bonded together by interatomic forces.

Diamond

The carbon in diamond takes a crystal lattice formation in which the carbon atoms are arranged in the shape of a tetrahedron. The spatial arrangement of a material determines its hardness and the firmness of its crystals. Diamond is the hardest mineral in nature, and is valued thanks to its strange and beautiful optical effects, the result of its glimmer, shape and cut, not to mention the fact that diamonds are quite rare. Diamonds are found in the shape of octahedrons or skewed 12-sided crystals, also with contorted sides. The most valuable diamonds are the ones that are completely translucent, colourless and strongly light reflective. Besides colourless diamonds, there are diamonds that are brownish, grey, greenish, and with a slightly blue or red tinge. The value of one unit of weight of a diamond is one carat (= 200g). Diamonds are used in the production of jewelry, among other things, but they must be polished. The most well-known shape of a polished diamond is called brilliant. Around 95% of all diamonds found on Earth are not used in jewelry at all, however, instead finding use as drill bits or cutting devices, due to their hardness.

Diamonds can also be made synthetically, but natural diamonds remain more prevalent, thanks to their rough surfaces which are used for cutting and drilling. It is possible to manufacture diamonds which are used in jewelry, but it is a very long, drawn-out process which costs more than it is actually worth.

Graphite

In graphite, the carbon atoms are arranged in layers. Compared to diamond, graphite’s hardness is negligible. It is an opaque, black, very soft substance with good electrical and heat conductivity. Graphite does not burn well.

Man-made graphite is made using the Acheson process, which is the reaction between the fuel coke and silicon are temperatures above 2000° C. It is also used as a blackening substance and a material in the production of electrodes and collectors, and as a moderating substance in nuclear reactors. Thanks to its layered structure, it is found in layers in the quarries where it is mined.

In diamond, the hydrogen atoms present are bonded with strong covalent bonds to the carbon atoms in the compound. Each carbon atom is bonded with four other carbon atoms. This explains diamond’s hardness and high boiling point.

Graphite is composed of carbon atoms in layers, flat. The carbon atoms in graphite are bonded together with three covalent bonds. Between the individual layers, however, the van der Waals forces holding the material together are very weak. For this reason, individual layers of graphite can separate from one another, which reduces the hardness of the whole material.

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Carbonic acid and carbonates

Carbonic acid (H₂CO₃) is a weak acid which occurs only in aqueous solution. It is sometimes mistakenly considered to be carbon dioxide (CO₂) in solution, because of the reaction which produces it: Carbonic acid is formed by the dissolving in water of carbon dioxide according to the reaction

CO₂+ H₂O ® H₂CO₃.

The salts of carbonates and hydrogen carbonates are found in the Earth’s crust.

Generally, hydrogen carbonates are formed by the union of a metal and the HCO₃ - group in a reaction which releases one atom of hydrogen (a proton). This means that one atom of hydrogen is replaced by one atom of a metal.

Carbonates are also the salts of carbonic acid, with the only difference that the original hydrogens in the carbon acid are replaced by two metal atoms. When this occurs, the general formula of the salt formed is M₂CO₃ . Two atoms of hydrogen are released when this type of molecule is formed.

Carbonates are most often found in non-living matter, usually in the Earth’s layers as rock-forming materials.

Calcium carbonate (CaCO₃) is one of the main minerals which is able to form other compounds. It is slow to dissolve in water, forming a more easily soluble hydrogen carbonate, which reverts to its former state, an insoluble, precipitated CaCO₃, when the water is evaporated out of the system.

This is the natural process which forms the beautiful stalactites that we see in caves all around the world.

Calcium carbonate is often called calcite. It is present in nature in numerous forms. It can be white or yellow, reddish, greenish or brownish, translucent or opaque. Clear calcite is an optically strong magnifier, so it was often used as an optical instrument in the past.

Another rock-forming compound is calcite. Most of the time, the products that it forms are called lime or limestones. Raw lime is transformed into quick lime at temperatures of over 1000° C. Any water mixed into the original substance forms hydrate of lime, or slack lime, which is used in the construction industry as an ingredient in cement and mortar.

Of course, many other carbonate compounds exist, most of which are found in the Earth’s crust. Many of their titles have been eternalised because of the fact that they are common geological materials, or because place names have been named after them: For example, dolomite in the southern Carpatian Mountains, which now belongs to Italy.

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The compounds of silicon

Silica sol, an acid containing silicon, glass, porcelain, bricks and mortar are some of the most important compounds which the element silicon forms.

Silicon is found in nature bonded in the form of silicon oxides which contain many complex

compounds. Many minerals are composed of silicon-containing compounds, among other materials.

Silicon is the second most common element in the Earth’s crust, at 25.8% . Silicon is not very reactive. Even its oxide, silicon oxide, can only be formed at high temperature.

Silica sol, which is the common name for the oxygenated silicon-containing acid, is found in nature in the form of its salts. The silica sol compound with the simplest formula is the short-lived mono silicon, also known as orthosilicon acid (H₄SiO₄). As water is drawn from the molecule (condensation), the hydrogen atoms once present are replaced by atoms of silicon. This new compound is called a polysilicon or metasilicon acid. When a certain degree of condensation is reached, the dissolved siliconic acids can transform into strongly hydrated colloidal silicon gels.

The building block of silicon rock is silicon oxide, which is arranged in a polymeric atomic lattice. Silicon is found in its pure form as a so-called mineral crystal, but it often contains impurities such as sand. When melted, the bonds between its atoms are broken, leading to the breakdown of the molecule. When cooled, an amorphic structure remains: This is glass. As glass forms, the fractures consolidate with the help of oxide ions. Glass is a fairly hard, mostly non-crystalline structure which is breakable. It is inorganic material which does not have one definite melting point, because with rising temperature it gradually softens until the point when it liquifies completely. From a structural point of view, glass is a spatially irregular web composed of certain elements. It has low heat conductivity and a high resistance to electricity. Glass can be formed at high temperature in a process that uses casting, blowing, pressing and rolling.

Glass can be used in a number of areas. Thanks to its characteristics, it is most often used as a vessel for various liquids and other materials (because it is not very reactive). It can be used in electronics as an insulating material for electrical current. If other foreign materials are added to glass, it will colour, or change hues (for example iron oxide will give glass a greenish hue). This often gives glass a decorative type of feeling.

The salts and esters of silica acid are known as silicates. Silicates contain, besides silicon and acid, metal ions including potassium ions, sodium ions as well as aluminum ions. These molecules can be spatially oriented in either one, two or three dimensional structures. For this reason, there are numerous silicates.

Natural silicates are reactants used in the production of artificial silicates, as in for example cement and porcelain. Clay is produced by the weathering of mica. Clay and lime are used to make cement, which hardens after mixing with water.

China clay, or kaolin, a colourless clay, is used in the production of porcelain. Kaolin is mixed with a silicon sand and feldspar. Either it is formed as needed in the beginning, then heated, which is the general process of pottery, or it is made into some other shape or form using some other industrial method. Ceramic products are often used in construction, as clay bricks or brick dust of one sort or another. Sand and ash matter are used to make bricks, formable or otherwise, shingles and even canalisation pipes. Fire resistant material is usually used. The processes that individual ceramics are made from differ only according to those products’ shaping. The desired shape can be attained by casting, pressing, smothering or in other various ways.

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Synthetic macromolecules

Synthetics are synthetic macromolecular compounds which are used in a variety of different ways. They replace materials such as natural fibres, wood, metals and glass. Some synthetic materials are the result of directed research, as in the production of plastics, with some desired combination of properties which might have some specific uses. Synthetics can be divided into three major categories, according to the way they behave when they are heated. We distinguish between thermoplastics, duroplastics and elastomers.

Thermoplastics soften when heated, liquifying in a certain temperature range. There is no chemical change in their structure. These macromolecules are composed of long, slightly branched chains which are held together with the help of van der Waals forces and hydrogen bonds. When heated, these forces between molecules are weakened, allowing the molecules to be able to push on each other and shift and move.

Duroplastics do not soften when heated. Their molecules are mutually strengthened with the help of paired electrons and the help of other bonds. At high temperature, these bonds do break, and the plastic begins to decompose.

Elastomers are synthetics which are easily formed mechanically. Once the stress is relieved, however, they return to their original shape. Their elasticity is caused by a web of arranged molecules with large spaces in between them. When heated, elastomers begin to shrivel, because their molecules begin to oscillate, and the network between them contracts. At high temperatures, elastomers break down.

Synthetics are used in almost every part of our daily lives. The reason is that they are materials which can be made to suit most any need. and this property of theirs is truly used to its utmost, as the various uses of the three types of developed plastics can attest to.

Colouring of materials

Electromagnetic waves of between 400 nanometers and 750 nanometers are in the visible spectrum of light, so they can be seen by the human eye. With a prism, these wavelengths can be broken down into the colours of the spectrum, with certain ranges of wavelengths corresponding to certain colours. Colours are seen when a certain spectrum absorbs a certain length of wave. This absorption leads to electrons being excited, or even a whole molecule being excited. Unabsorbed light is reflected and is seen as complementary colour. Organic dyes have functional groups with a number of bond types. Electrons p absorb light of visible wavelengths, so that material appears as a complementary colour. Colour given off by a group of atoms with multiple bonds is therefore called chromatic (chroma = Greek colour). The colour of a substance depends on the number and size of its chromophores.

Coloured indicators of pH

Some coloured substances change their colour according to pH. We call these acid and base indicators. They can be used to determine the pH of a solution, if not precisely. Colour change of an indicator is based on the transfer of protons between solution and indicator, which can cause a structural change in the indicator molecule. In most cases, colour changes because electrons p have been influenced by the presence of multiple bonds. Indictors exist in two forms - as an acid-base pair.

Acid-base indicator pair

Acidic form + H₂O ® basic form + H₃O⁺

According to the acidity or alkalinity of the solution, the equilibrium goes in one direction or the other. A visible change in the colour of the indicator only occurs when the concentration of the appropriate form of the indicator is increased a minimum of tenfold. For this reason, there are indicators for transition ranges, which indicate over a range of pH, not a specific one.

Laboratory indicators

phenolthalein range at pH 8.0-9.8 colourless to reddish purple
bromothymol blue range at pH 6.0-7.6 yellow to blue
methylorange range at pH 3.1-4.4 red to yellow-orange
Coloured molecules are called dyes. These can be divided into paints and pigments.

Paints are soluble molecules. Natural dyes can be produced from plant or animal matter. One well known example is saphran, which comes from the crocus flower. This dye is used as a yellow dye and as a spice. Natural colours are being replaced more and more often with synthetic colours. These colours are used first and foremost in the dyeing of textiles. Azure (blues) and anthracites are some of the most well-known examples. Azure-coloured dyes are characterised by the presence of a N=N double bond. Aniline is used to produce azure dyes, which are produced in two steps. In diazotaion are formed ions of phenyldiazone, which bonds in the following step with phenol or another aromatic amine. This combination of an aromatic amine produces an azure dye such as aniline yellow or chryzoid (yellow-brown).

Pigments do not dissolve in the basic ingredients of paints, instead forming suspensions. Pigments such as umbra? and ochre have been used for ages. Both are aluminum silicates which differ in the content of their oxides. Ochre contains iron oxide, and umbra? contains an additional manganese oxide. One of the most important synthetic pigments is a white pigment made from titanium oxide. Pigments are often used as colours employed in printing presses and printers.

Pigments used as printing press colours:

iron oxide red
chromium oxide green
Iron chromate yellow
cadmium sulfide yellow

Tensides, or surfactants

Tensides are those materials which show surface activity. These are used in a wide variety of ways, as cleaning products or as counter or other surface finishers. The oldest, most well known cleaning product is soap. It is made from fats and active sodium bases and water. It is able to breakdown the ester bonds between glycerine and carboxylic acids, which leads to water joining in. Reactive products such as glycerine and alkaline salts are oily acids. These are actually soaps. For this reason, we call this process saponification. The effects of soaps depend on the ion content in water. Calcium ions replace the other ions present and bond with carboxylic acids to form a not very soluble calcium soap (see Fig. 1), whose cleaning power is limited, because it sediments.

Because soaps have a variety of disadvantages, they were replaced early on by synthetic tensides. We can distinguish between anionic, cationic, non-ionic and amphoteric tensides.

Anionic tensides are produced from two greasy alcohols of esterified sulphuric acids. These esters are then neutralised with sodium hydroxide, so that a sodium salt of monoalkylsulphuric acid is produced.

Cation tensides are ammonium salts with long alkyline rests. These tend to bond on to negatively charged surfaces. They are produced in the reaction of carboxylic acid with ammonia, which results in the production of alkylamines which are then substituted in a reaction with methyl chloride, resulting in ammonia as a product. Cation tensides are used mostly as softeners.

Non-ionic tensides see a charged portion of their molecule replaced by an uncharged group. With alkylpolyglycolethers it is a polyester rest which creates a polar part of the molecule of the tenside.

Non-ionic tensides have good moistening effect even at low temperatures.

Amphoteric tensides have one cation group and one anion group at their polar end. These are called amphotensides as well. Because they do not cause a reaction in human beings, they are often used in cosmetic products.

Other cleaning agents

In order to dissolve surface impurities, the effects of lipophilic alkyl rests are used on dirt on the surface of a given object (Figure 2). These are negatively charged and therefore repel each other. Parts of the stain are removed by the lipophile end of the tenside molecule. These are simply surrounded and carted off by the cleaning molecule. In our modern lives, we place great emphasis on cleanliness and the products which clean up after us. These products, besides cleaning agents, contain a wide variety of additives. The quality of these is improving constantly. Think of all the wonderful uses: perfumes, enzymes, inhibitors, whiteners, softeners - all of which increase the performance of water.

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