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CHAPTER 1: CLASSIFICATION OF MATERIALS
A day at the park
1.1 WHY STUDY MATERIALS?
stone pedestal, concrete sidewalk, or grassy lawn? It probably depends on^ On a sunny day at the park, where would you prefer to sit and relax if you want to be-^ on a wooden bench, warm or cool. If you want to read, be thankful that you don't have to carry carved stone tablets or a parchment scroll; you can carry a paperback book in your backpack or download an ebook to a portable computer. Maybe you should take - a wool blazer, nylon windbreaker, microfiber trenchcoat, or cotton sweatshirt? People who are a jacket along. Which would be the best choice fortunate enough to have all of these in their closets can choose the material that best protects them from the predicted weather - temperature, precipitation, and wind. materials^ In modern society we are surrounded by an amazing variety of discussed in this book are solids that have been modified from their natural states to^ materials. Most of the make them mor The materials people use have such an impact on their lifestyles that historical eras havee suitable for practical applications.
to reveal the increasing sophis^ been named for them. Ancient artifacts found by archaeologists have been dated and analyzedtication of their manufacturing methods. Early humans ~9000 BCE Stone ageCopper ag e ~3000 BCE ~1200 BCE Bronze ageIron age
top row: flint handaxe, copper coin, bronze helmet^ Artifacts of civilization bottom row: locomotive wheel, plastic toy, solar cell and new weapons for armies. Explorers established trade routes to redistribute raw materials and^ Historians have shown that technological advancements created new tools for agriculture finished products. Modern culture is also influenced by the availability of new materials. In the 1960's plastics were used to make colorful toys and housewares at such a low cost that they were frequently disposed of and replaced with the latest style. In the 1980's silicon based electronics started spreading through businesses and homes. Since the 1960s homes (and landfills) in the United States have become bigger and more crowded with objects for applications never dreamed of by stone age humans. In the 21st century there is much discussion of "globalization." Materials definitely follow a global cycle. Raw materials are collected; processed into useful materials; sold to consumers; and eventually discarded as waste. Each stage may occur on a different continent! Supply and demand of materials can affect international relations.
Comparison of ceramic and polymer building materials best performance. However in an earthquake, the brick house would be the worst place to be!^ When the wolf huffed and puffed, the straw and stick houses fell down. Brick had the The reinforced concrete. vibrations can rattle the bricks apart. California’s building codes favor wood or steel- cold, heat, rain, snow, hail^ What should a good house material do? Protect the things inside from weather - and from fire. A medieval castle was designed to withstand^ -^ wind, cannonballs but since that is not usually a concern in modern construction, most people would decide that its superior performance is not worth the extra cost. PROPERTIES to consider the^ To choose a material with the best performance f properties of the available materials. Properties are the observed characteristicsor a particular application, we will need of a sample. Physical properties Hardness^ Some physical properties describe how an object responds to mechanical forces is one example of a mechanical property. If you drag a steel knife blade across a hard. object, such as a plate, the hard surface is unchanged; if you drag the blade across a soft object, such as a piece of chalk, the soft surface will be scratched. An object is tough if force is unable to break or tear it. The response to force depends on the material's structure, and also on its shape and size. A piece of notebook paper can be torn easily, but a telephone book requires much greater force. We can easily bend a flexible object such as a nylon jacket, but more force is required to bend a when the force is removed, we call it stiff object like a polyethylene milk jug. If an object returns to its original shape and size elastic. If the deformation remains, it is plastic. An object that breaks rather than bending is brittle.
windbreaker is strong, since pulling on it does not change its length. Sometimes the manner^ An object is^ strong^ if an applied force is unable to deform or break it. A nylon of applying a force makes a difference to the strength of an object. Ceramics can bear a lot of weight, but will break if stretched or bent. Nylon survives compression, pulling and twisting. are colorless, smooth, and shiny.^ Color ,^ texture , and^ reflectivity Electrical conductivity^ can be observed by shining l is detected by applying a voltageight on a sample. Mirrors across an object. Applying heat to a sample reveals its ability to (temperature at which a solid changes to liquid), and its boiling point conduct heat (temperature at which a, its melting point liquid changes to gas). Some properties are independent of the amount of sample. Melting point does not change if a sample is divided in half. Other properties, including with the amount of sample being studied. mass and volume , increase measurements. The basic units of the Metric System are presented in Appendix I.^ When observing properties in a laboratory, scientists use the Metric System of Mass is measured on a balance or scale. A ruler can be used to find the volume of a regularly shaped object.
Two paper clips have a mass of about 1 gram.^ A staple is just over 1 cm long.
width length
height Volume = length x width x height
Chemical properties These describe what chemical reactions are likely to occur. We can observe how a sample reacts when mixed with other chemicals ( described as flammable. Some materials rust (a type of oxidation reaction). Some materialswater, acid). A material that can burn is dissolve in water or other liquids. Usually a chemical reaction involves a transformation of the sample into a different substance, and it may be difficult to reverse the process. When it burns it combines with oxygen from the air. The reaction produces ashes, smoke and For example, wood is flammable. water; it cannot be reversed to make wood. properties from the original wood. The products of the reaction have quite different
Characteristic Properties of Major Classes metals hard but malleable polymersstiff or flexible ceramicshard but brittle shiny little color dullcolorl (^) ess shiny if glazedmany colors intermediate conduct electricity low meltingnonconductive highest melting pointnonconductive high density difficult to burn low densityflammable intermediate densitynot flammable
COMPOSITION reveal the chemical elements that are present in the sample.^ Composition^ tells what chemicals are in a sample. The most specific description will The simplest pieces chemists can make are at^ Chemists determined that matter is composed of combinations of about 100 elements.oms. Atoms of the same element are identical (have the same properties) and atoms of different elements are different. Some physical properties of elements are listed in Appendix II. Chemists can change oil into nylon only because they are composed of th The Periodic Table of the Elements lists all the known elements. Each element's squaree same elements. has its atomic number, name, and one or two letter chemical symbol. For example, 18 hydrogenoxygen HO Many different experimental in a sample. One of the most sophisticated techniques, techniques have been developed to test which elements are present X-Ray Photoelectron Spectroscopy (XPS), is described in Chapter 14. It is most often used to test metals and ceramics.
ceramic samples. The elements for metallic and polymeric materials do not overlap at all. This^ As shown^ in the figure, different sets of elements are found in metal, polymer and is one of the reasons that the properties of those two classes are so different. The in ceramics are also in found metals or polymers. elements found Compounds A compound has a uniform composition: every sample removed and tested, no matter how small, contains same elements in the same proportions. The elements in compounds are held together tightly and can only be separated from each other by chemical reactions. manner. It includes the chemical symbol for each element, listed from left to right as they appe^ A chemical formula relays the chemical composition of a compound in a compact ar on the Periodic Table. The symbol for each element is immediately followed with the number of atoms of that element as a subscript. Fe 2 O 3 contains two iron atoms and three oxygen atoms. If there is only one atom of the element, we do not bother to wri hydrogens and one oxygen, so its chemical formula is written Hte the number one. Water has two 2 O.
The elements hydrogen and oxygen, and the compound water.
1.4 HOW DOES ATOMIC STRUCTURE RELATE TO CHEMICAL PROPERTIES?
THE COMPONENTS OF AN ATOM
reactions cannot make them simpler. Each atom in a sample of an element has the same^ It has been mentioned that elements are the purest forms of chemicals. Chemical chemical properties. In 1897 it was discovered that atoms can be separated into negatively charged and po that one electron has a charge ofsitively charged parts. Electrons - 1. Electrons can be rearranged by chemical reactions. are the pieces with negative charge. Chemists usually say positively charged and contains most of mass of an atom. The positive charge of the nucleus^ If all the electrons are removed from an atom, what remains is the^ nucleus. It is attracts the negative charge of the electrons. Further experiments showed that a nucleus is composed of two types of particles. Each proton much larger masses than electrons. Neutrons and protons are held together so tightly that an in the nucleus has a charge of +1. A neutron has no charge. Both types of particle have atomic nucleus will not change during a chemical reaction. nucleus surrounded by cloud of electrons
Carbon always has six protons in its nucleus, but it can have six, seven or eight neutrons.
proton neutron
electrons. A carbon atom always has six protons and six electrons.^ Since an atom^ has no overall charge, its number of protons is equal to its number of The mass of an atom may be repo^ Atoms are so small that 6.02x10rted in atomic mass units (amu). 1 amu = 1.66x10^23 carbon atoms are needed to make a 12 gram sample!-^24 g. ATOMIC NUMBER AND THE PERIODIC TABLE found on the Periodic Table is the number of protons. Any atom with one prot^ The identity of an atom is determined by its number of protons. The atomic numberon is a hydrogen atom (with atomic number 1). Scientists have found atoms with as many as 116 protons in their nuclei, but the largest nuclei are unstable and not used for materials.
left- and right^ The order of elements on the table is the number of protons. Eleme-hand neighbors in mass and size. Elements farther down the periodic table shownts are similar to their an increase in mass and size. Notice that the rows labelled 1 through 7 (called “periods”) are not all the same length. The pattern same column (called a “group”) undergo similar reactions. For example, group I contains the provides information about the chemical properties of elements. Elements in the elements Li, Na, K which all react violently with water. The tallest groups, labelled with Roman numerals, contain the main group elements. The central section of the table, starting with element #21, contains two rows at the bottom of the table contain inner transition elements transition elements.. The Classes of elements Left/bottom corner: metals. These are almost all solids at room temperature. They are shiny and conduct electricity well. Right/top corner: non-metals. These are more often gas or liquid than solid; non- conductors. The last group on the right, labelled never react and do not form useful materials. VIII, contains the noble gases. These almost between those of metals and nonmetals. They are shiny, but too brittle to^ Along the diagonal division:^ semi-metals. These have properties that are intermediate make wires. Their most useful property is that they are semiconductors. This means that they conduct electricity under controlled conditions. Valence electrons The chemical properties of an element are determined by number of electrons available for reactions. The theory called quantum mechanics explains that electrons are arranged in shells
Learning Goals for Chapter 1 After studying this chapter you should be able to: Recall historic eras labeled by materials. Know the three major classes – Metals, Polymers, Ceramics. Give examples of, and common applications for, each class of material. Identify physical & chemical properties: what are they; which are common for each class of material. Know how to find the density of a sample. Use properties and composition to sort materials into classes. Use a Periodic Table in the following ways: find know what chemical relationships are found in groups and periods; numbers of protons, electrons, and atomic mass for an element; locate regions of metals, semimetals, and nonmetals; predict stable ions of main group elements. Use the metric system: know the basic units for length, volume, mass, and the prefixes. Vocabulary list atom ceramic atomic masscolor atomic numbercomposition conductivity electron densityelement elasticflexible hard metal ionneutron massnucleus plastic processing polymerproton performancereflectivity stiff tough strongvalence electron texturevolume
