Unit 3Text1.From the periodic table, it can be seen that there are only about 100 different kinds of atomsin the entire Universe. (Unit 3, P21, Para 1, Line 1)2.The atomic structure primarily affects the chemical, physical, thermal, electrical, magnetic,and optical properties.(Unit 3, P22, Para 5, Line 1)3.The microstructure and macrostructure can also affect these properties but they generallyhave a larger effect on mechanical properties and on the rate of chemical reaction. (Unit 3, P22, Para 5, Line 2)4.From elementary chemistry it is known that the atomic structure of any element is made upof positively charged nucleus surrounded by electrons revolving around it. (Unit 3, P22, Para 6, Line 1)5.An element’s atomic number indicates the number of positively charged protons in thenucleus.(Unit 3, P22, Para 6, Line 3)6.The atomic weight of an atom indicates how many protons and neutrons in the nucleus.(Unit 3, P22, Para 6, Line 4)7.It is also known that electrons are present with different energies and it is convenient toconsider these electrons surrounding the nucleus in energy “shell”.(Unit 3, P22, Para 7, Line 2)8.For example, magnesium, with an atomic number of 12, has two electrons in the inner shell,eight in the second shell and two in the other shell.(Unit 3, P22, Para 7, Line 4)9.All chemical bonds involve electrons.(Unit 3, P22, Para 8, Line 1)10.Atoms are at their most stable when they have no partially-filled electron shells. (Unit 3, P22,Para 8, Line 2)11.When metal atoms bond, a metallic bond occurs.(Unit 3, P23, Para 1, Line 1)12.The bond between two nonmetal atoms is usually a covalent bond.(Unit 3, P23, Para 1, Line4)13.Where metal and nonmetal atom come together an ionic bond occurs.(Unit 3, P23, Para 1,Line 4)Reading Material1.Ionic bonding occurs between charged particles.(Unit 3, P26, Para 1, Line 1)2.Metals usually have 1, 2, or 3 electrons in their outermost shell.(Unit 3, P26, Para 1, Line 2)3.Since electrons have a negative charge, the atom that gains electrons becomes a negativelycharged ion (i.e., anion) because it now has more electrons than protons. (Unit 3, P26, Para 2, Line 1)4.Alternately, an atom that loses electrons becomes a positively charged ion (i.e., cation).(Unit 3, P26, Para 2, Line 2)5.Fig 1.3 schematically shows the process that takes place during the formation of an ionicbond between sodium and chlorine atoms.(Unit 3, P26, Para 3, Line 1)6.Note that sodium has one valence electron that it would like to give up so that it wouldbecome stable with a full outer shell of eight.(Unit 3, P26, Para 3, Line 2)7.Also note that chlorine has seven valence electrons and it would like to gain an electron inorder to have a full shell of eight.8.The transfer of the electron causes the previously neutral sodium atom to become apositively charge ion (cation), and the previously neutral chlorine atom to become a negatively charged ion (anion).(Unit 3, P26, Para 3, Line 4)9.Nonmetals have 4 or more electrons in their outer shells (except boron). (Unit 3, P26, Para 5,Line 2)10.The more atoms in each molecule, the higher a compound’s melting and boilingtemperature will be.(Unit 3, P27, Para 3, Line 2)11.So, for example, when aluminum atoms are grouped together in a block of metal, the outerelectrons leave individual atoms to become part of common “electron cloud”. (Unit 3, P27, Para 5, Line 3)12.In this arrangement, the valence electrons have considerable mobility and are able to conductheat and electricity easily.(Unit 3, P27, Para 5, Line 5)13.This regular pattern of atoms is the crystalline structure of metals. (Unit 3, P28, Para 2, Line 4)14.In the crystal lattice, atoms are packed closely together to maximize the strength of thebonds.(Unit 3, P28, Para 2, Line 5)15.An actual piece of metal consists of many tiny crystals called grains that touch at grainboundaries.(Unit 3, P28, Para 2, Line 6)16.The van der Waals bonds occur to some extent in all materials but are particularly importantin plastics and polymers.(Unit 3, P28, Para 4, Line 1)17.These materials are made up of a long string molecules consisting of carbon atoms covalentlybonded with other atoms, such as hydrogen, nitrogen, oxygen, and fluorine. (Unit 3, P28, Para 4, Line 2)18.The covalent bonds within the molecules are very strong and ruptured only under extremeconditions.(Unit 3, P28, Para 4, Line 4)19.The bonds between the molecules that allow sliding and rupture to occur are called van derWaals forces.(Unit 3, P28, Para 4, Line 5)20.For example, in polyethylene the molecules are composed of hydrogen and carbon atoms inthe same ratio as ethylene gas.(Unit 3, P29, Para 2, Line 2)21.Polymers are often classified as being either a thermoplastic or a thermosetting material.(Unit 3, P29, Para 2, Line 6)Unit 4Text1.Properties that describe how a substance changes into a completely different substance arecalled chemical properties.(Unit 4, P31, Para 1, Line 3)2.Flammability and corrosion/oxidation resistance are examples of chemical properties. (Unit4, P31, Para 1, Line 4)3.When a material changes from a solid to a liquid to a vapor it seems like them become adifferent substance.(Unit 4, P31, Para 2, Line 2)4.However, when a material melts, solidifies, vaporizes, condenses or sublimes, only thestate of the substance changes.(Unit 4, P31, Para 2, Line 3)5.Phase is a physical property of matter and matter can exist in four phases: solid, liquid, gasand phasma.(Unit 4, P31, Para 2, Line 5)6.In general, some of the more important physical and chemical properties from an engineeringmaterial standpoint include phase transformation temperatures, density, specific gravity, thermal conductivity, linear coefficient of thermal expansion, electrical conductivity and resistivity, magnetic permeability, and corrosion resistance, and so on. (Unit 4, P31,Para 3, Line 1)7.Transitions from solid to liquid, from solid to vapor, from vapor to solid and visa versa arecalled phase transformations or transitions.(Unit 4, P31, Para 4, Line 2)8.Since some substances have several crystal forms, technically there can also be solid toanother solid form phase transformation.(Unit 4, P31, Para 4, Line 3)9.The phase transition temperature where a solid changes to a liquid is called the melting point.The temperature at which the vapor pressure of a liquid equals 1 atm (101.3 kPa) is called the boiling point.(Unit 4, P31, Para 5, Line 1)10.The temperature at which a solid, glassy material begins to soften and flow is called the glasstransition temperature.(Unit 4, P31, Para 5, Line 7)11.The space the mass occupies is its volume, and the mass per unit of volume is its density.(Unit 4, P32, Para 1, Line 1)12.Mass is a fundamental measure of the amount of matter. Weight is a measure of the forceexerted by a mass and this force is produced by the acceleration of gravity. (Unit 4, P32, Para 2, Line 1)13.Therefore, on the surface of the earth, the mass of an object is determined by dividing theweight of an object by 9.8 m/s2 (the acceleration of gravity on the surface of the earth). (Unit 4, P32, Para 2, Line 3)14.The density of liquids and gases is very temperature dependent.(Unit 4, P32, Para 3, Line 1)15.Some common units used for expressing density are grams/cubic centimeter,kilograms/cubic meter, grams/milliliter, grams/liter, pounds for cubic inch and pounds per cubic foot; but it should be obvious that any unit of mass per any unit of volume can be used.(Unit 4, P32, Para 4, Line 1)16.Specific gravity values for a few common substances are: Au, 19.3; mercury, 13.6; alcohol,0.7893; benzene, 0.8786.(Unit 4, P32, Para 5, Line 6)17.Magnetic permeability or simply permeability is the ease with which a material can bemagnetized.(Unit 4, P32, Para 6, Line 1)18.It is a constant of proportionality that exists between magnetic induction and magnetic fieldintensity.(Unit 4, P32, Para 6, Line 2)19.This constant is equal to approximately 1.257×10-6 Henry per meter (H/m) in free space (avacuum).(Unit 4, P32, Para 6, Line 3)20.Materials that cause the lines of flux to move farther apart, resulting in a decrease inmagnetic flux density compared with a vacuum, are called diamagnetic. (Unit 4, P32, Para 7, Line 1)21.Materials that concentrate magnetic flux by a factor of more than one but less than or equalto ten are called paramagnetic; materials that concentrate the flux by a factor of more than ten are called ferromagnetic.(Unit 4, P32, Para 7, Line 2)22.For non-ferrous metals such as copper, brass, aluminum etc., the permeability is the sameas that of “free space”, i.e. the relative permeability is one. For ferrous metals however the value of μr may be several hundred.(Unit 4, P33, Para 2, Line 1)23.This effect is useful in the design of transformers and eddy current probes. (Unit 4, P33, Para3, Line 2)Reading Material1.The electrons carry a negative electrostatic charge and under certain conditions can movefrom atom to atom.(Unit 4, P35, Para 1, Line 1)2.The directional movement of electrons due to an electromotive force is what is known aselectricity.(Unit 4, P36, Para 1, Line 3)3.It is the ratio of the current density to the electric field strength.(Unit 4, P36, Para 2, Line 2)4.Its SI derived unit is the Siemens per meter, but conductivity values are often reported aspercent IACS.(Unit 4, P36, Para 2, Line 2)5.IACS is an acronym for International Annealed Copper Standard or the material that wasused to make traditional copper-wire.(Unit 4, P36, Para 2, Line 4)6.Conductivity values in Siemens/meter can be converted to % IACS by multiplying theconductivity value by 1.724×10-6.(Unit 4, P36, Para 3, Line 1)7.Electricity conductivity is a very useful property since values are affected by such things as asubstance chemical composition and the stress state of crystalline structures. (Unit 4, P36, Para 4, Line 1)8.Electrical resistivity is the reciprocal of conductivity.(Unit 4, P36, Para 5, Line 1)9.The SI unit for electrical resistivity is the ohm meter.(Unit 4, P36, Para 6, Line 1)10.Resistivity values in microhm centimeters units can be converted to % IACS conductivityvalues with the following formula: 172.41 / resistivity = % IACS.(Unit 4, P36, Para 6, Line 5)11.Thermal conductivity (λ) is the intrinsic property of a material which relates its ability toconduct heat.(Unit 4, P36, Para 7, Line 1)12.Conduction takes place when a temperature gradient exists in a solid (or stationary fluid)medium.(Unit 4, P36, Para 7, Line 3)13.Thermal conductivity is defined as the quantity of heat(Q) transmitted through a unitthickness (L) in a direction normal to a surface of unit area (A) due to a unit temperature gradient (ΔT) under steady state conditions and when the heat transfer is dependent only on the temperature gradient.(Unit 4, P37, Para 2, Line 1)14.When heat is added to most materials, the average amplitude of the atoms’ vibrating withinthe material increases.(Unit 4, P37, Para 3, Line 1)15.As shown in the following equation, α is the ratio of change in length (Δl) to the totalstarting length (l i) and change in temperature (ΔT).(Unit 4, P37, Para 3, Line 6)16.By rearranging this equation, it can be seen that if the linear coefficient of thermalexpansion is known, the change in components length can be calculated for each degree of temperature change.(Unit 4, P37, Para 4, Line 1)17.That is to say, if energy is removed from a material then the object’s temperature willdecrease causing the object to contract. (Unit 4, P37, Para 4, Line 3)18.Thermal expansion (and contraction) must be taken into account when designing productswith close tolerance fits as these tolerances will change as temperature changes if the materials used in the design have different coefficients of thermal expansion. (Unit 4, P37, Para 5, Line 1)19.For example, thermostats and other heat-sensitive sensors make use of the property oflinear expansion.(Unit 4, P37, Para 5, Line 7)。