Chemistry and Measurement

All of the objects around you – your pen or pencil, and the things of nature such as rocks, water, and plants and animal substances – constitute the matter of the universe. Each of the particular kinds of matter, such as a certain kind of paper or plastic or metal, is referred to as a material. We can define chemistry as the science of the composition and structure of materials and of the changes that materials undergo.

One chemist may hope that by understanding certain materials, he or she will be able to find a cure for a disease or a solution for as environmental ill. Another chemist may simply want to understand a phenomenon. Because chemistry deals with  all materials, it is a subject of enormous breadth. It would be difficult to exaggerate the influence of chemistry on modern science and technology or on our ideas about our planet and the universe. In the section that follows, we will take a brief glimpse at modern chemistry and see some of the ways it has influenced technology, science, and modern thought.

Modern Chemistry: A brief Glimpse

For thousands of years, human being have fashioned natural materials into useful products. Modern chemistry certainly has its roots in the endeavor. After the discovery of fire, people begun to notice changes in certain rocks and minerals exposed to high temperatures. From these observations came the development of ceramics, glass, and metals, which today are among our most useful materials. Dyes and medicines were other early products obtained from natural substances. For example, the ancient.

Phoenicians extracted a bright purple dye, known as Tyrian purple, from a species of sea snail. One ounce of Tyrian purple required over 200,000 snails, because of its brilliant hue and scarcity, the dye became the choice of royalty.

Although chemistry has its roots in early technology, chemistry as a field of study based on scientific principles came into being only in the latter part of the eighteenth century. Chemists begun to look at the precise quantities of substances they used in their experiments. From this work came the central principle of substances they used in their experiments. from this work came the central principle of modern chemistry: the materials around us are composed of exceedingly small particles called atoms, and the precise arrangement of these atoms into molecules or more complicated structures accounts for the many different characteristics of materials. Once chemists understood this central principle, they could begin to fashion molecules to order. They could synthesize molecules; that is, they could build large molecules from small ones. Tyrian purple, for example, was eventually synthesized from the simpler molecule aniline.

The liquid-crystal displays (LCDs) that are used on everthing from watches and cell phones to computer monitors and televisions are an example of an application that depends on the special characteristics of materials. The liquid crystals used in these displays are a form of matter intermediate in characteristics between those of liquids and those solid crystals – hence the name. Many of these liquid crystals are composed of rodlike molecules that tend to align themselves something like the wood matches in a matchbox. The liquid crystals are held in alignment in layers by plates that have microscopic grooves. The molecules are attached to small electrodes or transistors. When the molecules are subjected to an electric charge from the transistor or electrode, they change alignment to point in a new direction, when they change direction, the change how light passes through their layer. When the liquid crystal layer is combined with a light source and color filters, incremental changes of alignment of the molecules throughout the display allow for images that have high contrast and millions of colors.

Chemists continue to develop new materials and discover new properties of old ones. Electronics and communications, for example, have been completely transformed by technological advances in materials. Optical-fiber cables have replaced long-distance telephone cables made of copper wire. Optical-fibers are fine threads of extremely pure glass. Because of their purity, these fibers can transmit laser light pulses for miles compared with only a few inches in ordinary glass. Not only is optical-fiber cable cheaper and less bulky than copper cable carrying the same information, but through the use of different colors of light, optical-fiber cable can carry voice, data, and video information at the same time. At the ends of an optical-fiber cable, devices using other new materials convert the light pulses to electrical signals and back, while computer chips constructed from still other materials process the signals.

Chemistry has also affected the way we think of the world around us, for example biochemists and molecular biologists -scientists who study the molecular basis of living organisms  – have made a remarkable finding: all forms of life appear to share many of the same molecules and molecular processes. Consider the information of inheritance, the genetic information that is passed on from one generation of organism to the next. Individual organisms, whether bacteria or human beings, store this information in a particular kind of molecule called deoxyribonucleic acid, or DNA.

DNA consists of two interwined molecular chains; each chain consists of links of four different types of molecular pieces, or bases, Just as you record information on a page by stringing together characters, an organism stores the information for reproducing itself in the order of these bases in its DNA. In a multicellular organism, such as a human being, every cell contains the same DNA.



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