Types of Chemical Substances

Finally we have the metals, made entirely of electropositive atoms. We g n f.hat these atoms are held together bv the metallic bond, similar to the valent hnnHa hut, without the properties of saturation. Thus the metals, like the ionic crystals and the silicates, tend to form indefinitely large structures, crystals or liquids, and tend to have high melting and boiling points and great mechanical strength. We have already seen that the same peculiarity of the metallic bond which prevents the saturation of valence, and hence which makes crystal formation possible, also leads to metallic conduction or the existence of free electrons. 

With this brief summary, we have covered most of the important types of materials. In the next chapter we shall make a detailed study of ionic substances, and in succeeding chapters of the various other sorts of materials, interpreting their properties in terms of interatomic and inter-molecular forces. 

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Antibiotic A specific type of chemical substance that is administered to fight infections usually caused by bacteria, in humans or animals. Many antibiotics are produced by microorganisms some are chemically synthesized. 

In the early days of chemistry, the list of known compounds was short, so chemists could memorize the names of all of them. New compounds were often named for their place of origin, physical appearance, or properties. As the science of chemistry grew, the number of known compounds increased quickly. Soon, nobody could keep track of all of the common names. Today, more than 20 million compounds are known, and thousands of new ones are discovered or created each year. Consequently, chemists need systematic procedures for naming chemical compounds. The International Union of Pure and Applied Chemistry (lUPAC) has established uniform guidelines for naming various types of chemical substances, and chemists increasingly use lUPAC-approved names rather than their common counterparts. Systematic names are less colorful than common names, but they make chemistry less hectic because it is much easier to learn a few systematic guidelines than to memorize the names of thousands of individual compounds. 

In addition to the ability of certain substances to combine with the products of the decomposition of nitrocellulose, it is possible that the same or other substances may have a positive or a negative catalytic effect and may hasten or retard the decomposition by their presence. But it has not yet been made clear what types of chemical substance hasten the decomposition or why they do so. Nitrogen dioxide hastens it. Pyridine hastens it, and a powder containing 2 or 3% of pyridine will inflame spontaneously if heated for half an hour at 110°. Powders containing tetryl are very unstable, while those containing 10% of trinitronaphthalene (which does- not react with the products of decomposition) are as... 

Because of the very thin, soft, and hydrated nature of baby skin, most types of chemical substances are easily permeable. In general, areas subject to a high concentration of moisture and soiling agents may provide a favorable environment for bacterial colonization. Areas of baby skin such... 

The overall effect of this complex of factors is particularly important in the case of pesticides, since their mobility in the environment and their biological effects are connected with their adsorption. The general principles Involved in the study of pesticide adsorption are, however, valid in general and they are also relevant to the remaining types of chemical substances. 

Modern chemistry dates back to the 18th century and is therefore not a very old practice, but the principles of how to gain knowledge through experiments and observations on different types of chemical substances go back for more than two thousand years for alchemy (Figure 13.11). 

OWL OWL is a valuable and flexible web-based homework system and assessment tool. Using a question-creation format that varies the amount and type of chemical substance for each online session, OWL can generate more than 100,000 chemistry questions correlated to the book. Instant feedback helps you immediately assess your progress. OWL is available for use only within North America.)... 

The potential of these axially chiral HPMC nanospheres to encapsulate different types of chemical substances was also explored [20] in a set of experiments that proved their capacity to incorporate a number of inorganic and organic compounds. 

Some types of chemical substances are represented in a disconnected type of format consisting of two or more separate components. Two examples of such substances are illustrated in Figure 3. One example illustrates the salt of a base, cyclohexylamine sulfate salts of both acids and bases are treated in this manner. The other example is that of a polymer, which is expressed in terms of the component monomers. Each component is separately and uniquely identified by a CAS Registry Number, and the total substance is also given a separate CAS Registry Number. 

The most suitable method of fast and simple control of the presence of dangerous substances is analytical detection by means of simplified methods - the so-called express-tests which allow quickly and reliably revealing and estimating the content of chemical substances in various objects. Express-tests are based on sensitive reactions which fix analytical effect visually or by means of portable instalments. Among types of indicator reactions were studied reactions of complex formation, oxidation-reduction, diazotization, azocoupling and oxidative condensation of organic substances, which are accompanied with the formation of colored products or with their discoloration. 

The first strategy is to rmdertake a superficial scan of mainstream textbooks that everyday situations have been connected to cormnon school chemistry textbooks. For example, student-exercises may contain informatiorr, about contaminants in a river such as lead salts, about acid-base indicators in plants or about food additives for the preservation of wine. However, implicit confusion may (and frequently will) occur when the textbook and the teacher aim at reaching the right answer, for example the correct calculation of the concentration of an additive in gram per litre or parts per million (ppm). Students may still pose questions such as How many glasses of wine can I drink before 1 will get sick What is the effect of alcohol on my body Why is the addition of sulphite to wine important Is the same fact tme for red wine Or even further Shouldn t the government prohibit the addition of sulphite In this way students can become personally involved in subjects that can be related to their learning of chemical substances, and even to atoms and molecules. But, the student-activities in mainstream school chemistry textbooks often are not focused on this type of involvement they do not put emphasis in the curriculum on personal, socio-scientific and ethical questions that are relevant to students lives and society. 

The speed with which taste stimulation occurs, coupled with the fact that stimulation with toxic substances does no damage to the receptors, led Beidler to suggest that taste stimulus need not enter the interior of the taste cell in order to initiate excitation. Because a taste cell has been shown to be sensitive to a number of taste qualities, and to a large number of chemical stimuli, he and his coworkers concluded that a number of different sites of adsorption must exist on the surface of the cell. Therefore, they assumed that taste response results from adsorption of chemical stimuli to the surface of the receptor at given receptor sites. This adsorption is described by a monomolecular reaction similar to that assumed by Renqvist, Lasareff, and Hahn, but with a difference. From the fact that each type of chemical-stimulus compound has a unique level of saturation of the taste receptor, it was concluded that the magnitude of the response is dependent on the initial reaction with the receptor, and not on other, subsequent receptor-reactions that are common to all types of receptor stimulation. Therefore, it was assumed that the magnitude of neural response is directly proportional to the number of sites filled, the maximum response occurring when all of the sites are filled. Beidler derived a fundamental... 

Moist potassium peroxodisulphate was accidentally exposed to traces of potassium hydroxide. It combusted spontaneously, causing the installations to catch fire. It is impossible to put out a fire involving this peroxydic compound with carbon dioxide or extinguishing powders although these agents are suitable for fires of chemical substances. Only water, which is usually not recommended in this case, can put out this type of fire. 

Solvent selectivity refers to the ability of a chromatographic system to separate two substances of a mixture. It depends on the chemistry of the adsorbent surface, such as the layer activity and type of chemical modihcation. The separation power or resolution is given by Equation 4.8 [27] ... 

OSL Acronym for optically stimulated luminescence. oven A furnace used at relatively low temperatures, overglaze Pigment applied to the surface of pottery after glazing. oxidation A type of chemical reactions in which an atom or atomic group combines with oxygen or one or more electrons are removed from it. oxide A substance composed by the chemical combination of oxygen with another element. 

The identification of chemical substances by examination of their spectra (singular, spectrum). Both infrared and ultraviolet spectroscopy are used in the study of rubber problems such as identifying the type of polymer or the nature of a contaminant. 

As the analytical, synthetic, and physical characterization techniques of the chemical sciences have advanced, the scale of material control moves to smaller sizes. Nanoscience is the examination of objects—particles, liquid droplets, crystals, fibers—with sizes that are larger than molecules but smaller than structures commonly prepared by photolithographic microfabrication. The definition of nanomaterials is neither sharp nor easy, nor need it be. Single molecules can be considered components of nanosystems (and are considered as such in fields such as molecular electronics and molecular motors). So can objects that have dimensions of >100 nm, even though such objects can be fabricated—albeit with substantial technical difficulty—by photolithography. We will define (somewhat arbitrarily) nanoscience as the study of the preparation, characterization, and use of substances having dimensions in the range of 1 to 100 nm. Many types of chemical systems, such as self-assembled monolayers (with only one dimension small) or carbon nanotubes (buckytubes) (with two dimensions small), are considered nanosystems. 

RTECS Registry of Toxic Effects of Chemical Substances number is a unique and unchanging number used to cross-reference the RTECS database, which is a compendium of data extracted from the open scientific literature. Six types of toxicity data are included in each file (1) primary irritation, (2) mutagenic effects, (3) reproductive effects, (4) tumorigenic effects, (5) acute toxicity, and (6) other multiple dose toxicity. 

Medard, L. Accidental Explosions, Vol. 1 Physical and Chemical Properties, Vol. 2 Types of Explosive Substances, Ellis Horwood Ltd., Chichester 1989 (engl. Ubers.)... 

Level C protection should be selected when the type of airborne substance(s) is known, concentration is measured, criteria for using air-purifying respirators are met, and skin and eye exposure are unlikely. It involves a full face piece, air-purifying, canister-equipped respirator and chemical-resistant clothing. This level of protection provides the same degree of skin protection as Level B, but a lower level of respiratory protection. 

Manufacturers, processors and/or distributors of chemical substances in the chemical industry are faced with three basic types of TSCA-mandated information situations ... 

Numerous types of chemical reactions pose potential hazards. Literature and incident data highlight the hazards of common industrial reactions, such as polymerization, decomposition, acid-base, oxidation-reduction (redox), and reactions with water. Polymerization and decomposition can be classified as self-reactions because they often involve just one chemical substance. However, other... 

Laboratory analysis of site soils should be made to determine the presence and population density of naturally occurring microbes that are capable of degrading the contaminant. At a minimum, these analyses should include plate counts to determine the relative number of microbes of several types, the substrate (food) type that reflects the type of chemicals they are likely to consume, and if toxic substances are present. 

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