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We also have Bitesize study guides covering many subjects at National 4 and National 5 on our Knowledge & Learning BETA website. All of the calculations in this section will be worked out using the distance, speed and time equation.
Chemistry is such a broad subject and one so full of detail that it is easy for a newcomer to find it somewhat overwhelming, if not intimidating. The real importance of Chemistry is that it serves as the interface to practically all of the other sciences, as well as to many other areas of human endeavor.
Chemistry can similarly be approached in different ways, each yielding a different, valid, (and yet hopelessly incomplete) view of the subject. This view of Chemistry is a rather astringent one that is probably more appreciated by people who already know the subject than by those who are about to learn it, so we will use a somewhat expanded scheme to organize the fundamental concepts of chemical science. Chemistry is the study of substances; their properties, structure, and the changes they undergo. Chemistry, like all the natural sciences, begins with the direct observation of nature— in this case, of matter. This dichotomy between what we can and cannot directly see constitutes two contrasting views which run through all of chemistry, which we call macroscopic and microscopic. The macroscopic world is the one we can know by direct observations of physical properties such as mass, volume, etc. In science it is necessary to know exactly what we are talking about, so before we can even begin to consider matter from a chemical point of view, we need to know something about its composition; is the stuff I am looking at a single substance, or is it a mixture? The idea of a minimal unit of chemical identity that we call an element developed from experimental observations of the relative weights of substances involved in chemical reactions. The definition of an element given above is an operational one; a certain result (or in this case, a non-result!) of a procedure that might lead to the decomposition of a substance into lighter units will tentatively place that substance in one of the categories, element or compound. The atom, by contrast, is a microscopic concept which in modern chemistry relates the unique character of every chemical element to an actual physical particle. The idea of the atom as the smallest particle of matter had its origins in Greek philosophy around 400 BCE but was controversial from the start (both Plato and Aristotle maintained that matter was infinitely divisible.) It was not until 1803 that John Dalton proposed a rational atomic theory to explain the facts of chemical combination as they were then known, thus being the first to employ macroscopic evidence to illuminate the microscopic world.
The formula of a substance expresses the relative number of atoms of each element it contains. What the ordinary chemical formula does not tell us is the order in which the component atoms are connected, whether they are grouped into discrete units (molecules) or are two- or three dimensional extended structures, as is the case with solids such as ordinary salt.
Substances are defined at the macroscopic level by their formulas or compositions, and at the microscopic level by their structures.
The elements hydrogen and oxygen combine to form a compound whose composition is expressed by the formula H2O.
One of the important characteristics of a compound is that the proportions by weight of each element in a given compound are constant. A molecule is an assembly of atoms having a fixed composition, structure, and distinctive, measurable properties. In its most general meaning, the term molecule can describe any kind of particle (even a single atom) having a unique chemical identity. Molecules suddenly became real in 1905, when Albert Einstein showed that Brownian motion, the irregular microscopic movements of tiny pollen grains floating in water, could be directly attributed to collisions with molecule-sized particles. The original article was publshed in Science magazine; see here for an understandable account of this historic work. A molecule but not a compound - Ozone, O3, is not a compound because it contains only a single element.
Composition and structure lie at the core of Chemistry, but they encompass only a very small part of it.
For a more in-depth treatment of much of the material covered here, please see The basics of atoms, moles, formulas equations, and nomenclature.
Chemical change is defined macroscopically as a process in which new substances are formed. Elemental chlorine exists as the diatomic molecule Cl2 in the gas, liquid, and solid states; the major difference between them lies in the degree of organization. Since the basic molecular units remain the same in all three states, the processes of melting, freezing, condensation and vaporization are usually regarded as physical rather than chemical changes. When heated above 801°C, the solid melts to form a liquid consisting of these same ions. Salt dissolves in water to form a solution containing separate Na+ and Cl– ions to which are loosely attached varying numbers of H2O molecules. Because the ions in the solid, the hydrated ions in the solution, and the molecule Na2Cl2 are really different chemical species, so the distinction between physical and chemical change becomes a bit fuzzy. An equation of this kind does not imply that the reactants A and B will change entirely into the products C and D, although in many cases this will be what appears to happen. The most important question we can ask about any reaction is "what is the equilibrium composition"?
This is very much a macroscopic view because the properties we need to directly concern ourselves with are those of the reactants and products. Virtually all chemical changes involve the uptake or release of energy, usually in the form of heat. The energetics of chemical change that we discussed immediately above relate to the end result of chemical change: the composition of the final reaction mixture, and the quantity of heat liberated or absorbed.
Does the reaction take place in a single step, or are multiple steps and intermediate structures involved? For example, the reaction between nitric oxide and hydrogen (identified as the net reaction at the bottom left), is believed to take place in the two steps shown here. Mechanisms, unlike energetics, cannot be predicted from information about the reactants and products; chemical theory has not yet advanced to the point were we can do much more than make educated guesses.
Because we cannot directly watch the molecules as they react, the best we can usually do is to infer a reaction mechanism from experimental data, particularly that which relates to the rate of the reaction as it is influenced by the concentrations of the reactants.


Catalysts can make dramatic changes in rates of reactions, especially in those whose un-catalyzed rate is essentially zero. A surprisingly large part of chemistry has to do with isolating one component from a mixture. A large amount of research is devoted to finding more accurate and convenient means of identifying substances. Atomic emission spectrophotometry, another widely-employed spectroscopy method, analyzes the light emitted by the various atoms in a substance.
The red lines at the right show how this molecule was broken into the ionized fragments that resulted in the spectrum shown at the left.
NMR is one of the most commonly employed tools for determining the structure of a molecule.
Materials science attempts to relate the physical properties and performance of engineering materials to their underlying chemical structure with the aim of developing improved materials for various applications.
Fullerenes were first identified in 1985 as products of experiments in which graphite was vaporized using a laser, work for which R.
This field covers a wide range of studies ranging from fundamental studies on the chemistry of gene expression and enzyme-substrate interactions to drug design. This field is now highly automated and usually involves combinatorial chemistry (see below) combined with innovative separation and assay methods.
But this is only the first step; a promising drug lead must then be intensely studied to make sure that it can actually be turned into a practical drug. Once a drug candidate has been found, its molecular structure can often be modified in order to ohydrate structure.
This huge field focusses on the relations between structure and function of proteins— of which there are about 400,000 different kinds in humans. In its most general sense, this word refers to any reaction that leads to the formation of a particular molecule. Make sure you thoroughly understand the following essential concepts that have been presented above. Define the following terms, and classify them as primarily microscopic or macroscopic concepts: element, atom, compound, molecule, formula, structure.
This chapter covers the following topics: scope of chemical science,chemical composition,chemical change, energetics and dynamics of chemical reactions,currents of modern Chemistry. What makes for the unity of all of electrodynamics is Maxwell's equations plus Lorentz Force Law. According to Maxwell's equations, electromagnetic radiation ( EM ) is a self - propagating transverse wave with electric and magnetic components where the oscillating electric and magnetic field components induce their respective opposites and vice-versa.
An easy way to remember the distance, speed and time equations is to put the letters into a triangle. Have paper and a pen handy, draw the distance, speed and time triangle on your paper, then try the examples. But the distincion can get pretty fuzzy; it is ultimately rather futile to confine any aspect of human endeavour to little boxes.
Chemistry is so deeply ingrained into so many areas of business, government, and environmental management that some background in the subject can be useful (and able to give you a career edge as a team member having special skills) in fields as varied as product development, marketing, management, computer science, technical writing, and even law. More importantly, this aspect of chemistry controls the direction in which change occurs, and the mixture of substances that results. It is of course only one of many ways of looking at the subject, but you may find it a helpful means of organizing the many facts and ideas you will encounter in your study of Chemistry. Because this operation is carried out on bulk matter, the concept of the element is also a macroscopic one.
In the 1920's it became possible to measure the sizes and masses of atoms, and in the 1970's techniques were developed that produced images of individual atoms. Because the formula can be determined by experiments on bulk matter, it is a macroscopic concept even though it is expressed in terms of atoms.
The microscopic aspect of composition is structure, which in its greatest detail reveals the relative locations (in two or three dimensional space) of each atom within the minimum collection needed to define the structure of the substance. Since the concept of an element is macroscopic and the distinction between elements and compounds was recognized long before the existence of physical atoms was accepted, the concept of a compound must also be a macroscopic one that makes no assumptions about the nature of the ultimate . Even at the end of the 19th century, when compounds and their formulas had long been in use, some prominent chemists doubted that molecules (or atoms) were any more than a convenient model.
In 2009, IBM scientists in Switzerland succeeded in imaging a real molecule, using a technique known as atomic force microscopy in which an atoms-thin metallic probe is drawn ever-so-slightly above the surface of an immobilized pentacene molecule cooled to nearly absolute zero. What is actually being imaged is the surface of the electron clouds of the molecule, which consists of six hexagonal rings of carbon atoms with hydrogens on its periphery. Thus the formulas CO, CH4, and O2 represent the molecules carbon monoxide, methane, and dioxygen. It is built from interpenetrating lattices of sodium and chloride ions that extend indefinitely.
It is largely the properties of chemical substances that interest us; it is through these that we experience and find uses for substances, and much of chemistry-as-a-science is devoted to understanding the relation between structure and properties. Take some time to look it over and make sure you understand all the terms and the relations between them.
In the gas the molecules move about randomly, whereas in the solid they are constrained to locations in a 3-dimensional lattice. This liquid boils at 1430° to form a vapor made up of discrete molecules having the formula Na2Cl2. Most chemical reactions proceed to some inermediate point that yields a mixture of reactants and products. But if you stop to think of the huge number of possible reactions between the more than 15 million known substances, you can see that it would be an impossible task to measure and record the equilibrium compositions of every possible combination.
One or two directly measurable properties of the individual reactants and products can be combined to give a number from which the equilibrium composition at any temperature can be easily calculated.


It turns out that these energy changes, which are the province of chemical thermodynamics, serve as a powerful means of predicting whether or not a given reaction can proceed, and to what extent. Notice that the nitrous oxide, N2O, is formed in the first step and consumed in the second, so it does not appear in the net reaction equation. To make matters even more complicated (or, to chemists, interesting!), the same reaction can often proceed via different mechanisms under different conditions. For example, the gaseous elements hydrogen and chlorine can remain mixed together in the dark indefinitely without any sign of a reaction, but in the sunlight they combine explosively.
This may occur at any number of stages in a manufacturing process, including the very critical steps involved in removing toxic, odiferous, or otherwise undesirable by-products from a waste stream. This ancient technique (believed to have originated with Arabic alchemists in 3500 BCE), is still one of the most widely employed operations both in the laboratory and in industrial processes such as oil refining. A common laboratory tool for isolating substances from plants and chemical reaction mixtures. Just as the progress of people walking through a shopping mall depends on how long they spend looking in the windows they pass, those molecules that adsorb more strongly to a material will emerge from the chromatography column more slowly than molecules that are not so strongly adsorbed. In the example shown here, the light is in the infrared range, which excites spring-like motions of chemically-bonded atoms. The resulsing beam passes through a magnetic field which deflectes them into individual components according to their charge-to-mass ratios.
The rightmost peak, representing CH3 hydrogens, is three times as high as the leftmost peak, reflecting the smaller abundance of -OH hydrogens. Its molecular structure can often be modified in order to optimize properties such as solubility, toxicity, and potency.
By means of computerized molecular modeling, a candidate drug molecule is developed that can bind to the target and, in so doing, modify its behavior. Proteomics is related to genetics in that the DNA sequences in genes get decoded into proteins which eventually define and regulate a particular organism. You have just completed a whirlwind tour of the world of Chemistry, condensed into one quick and painless lesson— the world's shortest Chemistry course! These electric and magnetic components oscillate at right angles to each other and propagate perpendicularly to the direction in which they indefinitely travel unless absorbed by intervening matter. The extent to which a given structure can persist is itself determined by energetics and dynamics. In order to improve the image quality, a molecule of carbon monoxide was placed on the end of the probe.
The tiny bumps that correspond to these hydrogen atom attest to the remarkable resolution of this experiment. However, the fact that we can write a formula for a compound does not imply the existence of molecules having that composition. For some purposes it is convenient to distinguish between chemical properties and physical properties, but as with most human-constructed dichotomies, the distinction becomes more fuzzy as one looks more closely. In the liquid, this tight organization is relaxed, allowing the molecules to slip and slide around each other. Moreover, all we need in order to make this prediction is information about the energetic properties of the reactants and products; there is no need to study the reaction itself. H2O2 is a by-product of respiration that is poisonous to living cells which have, as a consquence, evolved a highly efficient enzyme (a biological catalyst) that is able to destroy peroxide as quickly as it forms. But even in the research lab, a considerable amount of effort is often devoted to separating the desired substance from the many components of a reaction mixture, or in separating a component from a complex mixture (for example, a drug metabolite from a urine sample) prior to measuring the amount present. Practical uses include processing of radioactive wastes and decaffienation of coffee beans.
Each kind of atoms produces a characteristic line spectrum that uniquely identifies it. Mercury-vapor lamps (Hg), also used in outdoor lighting, have their strongest emission lines in the blue region, accounting for their characteristic hue. A detector at the end of the beam then measures the intensity of each component and sends this information to a computer which plots out the mass spectrum. This process can take years, and failure rates are very high; the cost of bringing a new drug to market is often as much as $100 million. Yes, we left out a lot of the details, the most important of which will take you a few months of happy discovery to pick up. That is, each kind of field - electric and magnetic - generates the other in order to propagate the entire composite structure moving forward through empty space at the finite speed of light, c.
Then take a look at BASIC CHEMISTRY and follow it as an outline for studying the other subjects in the top menu table above. Because these are bulk properties of matter, chemical thermodynamics is entirely macroscopic in its outlook. Some intermediates are unstable species, often distorted or incomplete molecules that have no independent existence; these are known as transition states. Because a thorough exploration of this would lead us into far more detail than we can accommodate here, we will mention only a few of the areas that have emerged as being especially important in modern chemistry. The separatory funnel shown here is the simplest apparatus for liquid-liquid extraction; for solid-liquid extraction, the Soxhlet apparatus is commonly used.
This serves as an important tool in the laboratory, where exitation is provided by a flame or an electrical discharge.
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