Chemistry of Engineering PDF

Chemistry of Engineering Types of Unit Cells CRYSTAL STRUCTURES CATEGORIES OF SOLIDS 1. Crystalline Type of solid where the atoms, ions, or molecules are arranged in an ordered and repeating pattern called a crystal lattice....

Chemistry of Engineering Types of Unit Cells CRYSTAL STRUCTURES CATEGORIES OF SOLIDS 1. Crystalline Type of solid where the atoms, ions, or molecules are arranged in an ordered and repeating pattern called a crystal lattice. SUMMARY They have geometric shapes 1. Simple Cubic (SC) They are firm, hold a definite and fixed shape, rigid and Description: Atoms are located at the corners of a cube. incompressible. Coordination Number: 6 (each atom touches 6 neighbors). The intermolecular forces are uniform and Atoms per Unit Cell: 1 (each corner atom contributes 1/8​). long-range because the particles are arranged in an Atomic Packing Factor (APF): ~0.52. orderly, repeating pattern. High melting and boiling point 2. Face-Centered Cubic (FCC) Ex: Quartz, Salt, and Diamond Description: Atoms at the corners and at the center of each face of the cube. Coordination Number: 12 (each atom touches 1 neighbors). 2. Amorphous Atoms per Unit Cell: 4 (3 from the faces and 1 from the corners). APF: ~0.74. The arrangement of particles is random and irregular 3. Body-Centered Cubic (BCC) Has rigid structures but lack a well-defined shape Description: Atoms at the corners of a cube, with one atom at the Do not have geometric shape center of the cube. The intermolecular forces are weak and variable due to Coordination Number: 8 (each atom touches 8 neighbors). the irregular arrangement of particles. Atoms per Unit Cell: 2 (1 from the center and 1 from the corners). Low melting and boiling point APF: ~0.68. Ex: Glass, Plastic, and Rubber 4. Hexagonal Close-Packed (HCP) UNIT CELLS Description: Atoms are packed in a hexagonal arrangement, with two layers of atoms above and below the hexagonal base. Coordination Number: 12. Atoms per Unit Cell: 6. APF: ~0.74. TYPES OF CRYSTALS In determining the structures and properties of crystals, such as melting point, density, and hardness it is important to consider the kinds of forces that hold the particles together. The classification of any crystal has four types: 1. Ionic 2. Covalent 3. Molecular 4. Metallic Ionic Crystals There are two important characteristics of ionic crystals and they are as follows: (1) They are composed of charged species (2) anions and cations are generally quite different in size. The radii of the ions must be known because it is helpful in understanding the structure and stability of these compounds. It is hard to measure the radius of an individual ion but sometimes it is possible to come up with an estimation. Covalent Crystals General Properties of Crystals AMORPHOUS SOLIDS Molecular Crystals Metallic Crystals Metals Occurrence of Metals Introduction to Metals Metal is an element, compound or alloy that is a good conductor of both electricity and heat. Metal crystal structure and specific metal properties are determined by holding together the atoms of a metal. An ore is a mineral or a combination of minerals from With the exception of hydrogen, all elements that form which metal or other valuable resources can be extracted positive ions by losing electrons during chemical profitably. In simple terms, ores are minerals that contain a reactions are called metals. sufficient amount of a metal or other substance that can be They are characterized by bright luster, hardness, ability extracted and used. to resonate sound and are excellent conductors of heat and electricity. Metals are solids under normal conditions except for Mercury. Mercury (Hg) is liquid at room temperature. Physical Properties of Metal State: Metals are solids at room temperature with the exception of Hg, which is liquid at room temperature (Ga is liquid on hot days). Luster: Metals have the quality of reflecting light from their surface and can be polished e.g., Au, Ag and Cu. Malleability: Metals have the ability to withstand hammering and can be made into thin sheets known as foils. Ductility: Metals can be drawn into wires. For example, 100 g of silver can be drawn into a thin wire about 200 meters long. Hardness: All metals are hard except sodium and potassium, which are soft and can be cut with a knife. Valency: Metals typically have 1 to 3 electrons in the outermost shell of their atoms. Ductility: Metals can be drawn into wires. For example, 100 g of silver can be drawn into a thin wire about 200 Principal Types of Minerals meters long. Hardness: All metals are hard except sodium and potassium, which are soft and can be cut with a knife. Valency: Metals typically have 1 to 3 electrons in the outermost shell of their atoms.Conduction: Metals are good conductors because they have free electrons. Silver and copper are the two best conductors of heat and electricity. Lead is the poorest conductor of heat. Bismuth, mercury and iron are also poor conductors. Density: Metals have high density and are very heavy. Iridium and osmium have the highest densities whereas lithium has the lowest density. Melting and Boiling Points: Metals have high melting and boiling points. Tungsten has the highest melting and boiling points whereas Metallurgy mercury has the lowest. Sodium and potassium also have low melting points. Electropositive Character: Metals tend to have low ionization energies, and typically lose electrons (i.e. are oxidized) when they undergo chemical reactions. They normally do not accept electrons. For example: Alkali metals are always 1+(lose the electron in s subshell) Principal steps Alkaline earth metals are always 2+ (lose both electrons in s subshell) Transition metal ions do not follow an obvious pattern, 2+is common (lose both electrons in s subshell), and 1+ and 3+ are also observed Production of metal 1. Conductors Band Gap: Negligible or Zero The Valence Band and The conduction band either overlap or are extremely close to each other. This means there is no significant band gap. As a result, electrons are free to move from the valence band to the conduction Conducts electricity Examples: Copper (Cu), Gold (Au), and Silver (Ag) 2. Insulators Band Gap: Large Large band gap Electrons cannot move freely Ineffective conductors of electricity Examples: Rubber, Glass, and Diamond 3. Semiconductors Band Gap: Small Principal Steps Normally are not conductors, but will conduct electricity. They have properties in between those of normal conductors and insulators. How semiconductors conduct electricity: 1. At higher temperature 2. Doping - a process where small amounts of other elements are added. Two Broad Categories of Semiconductors 1. Intrinsic semiconductors Band Theory of Electrical Conductivity 2. Extrinsic semiconductors Band theory – A model use to study metallic bonding - Explains how electrons in solids contribute to the flow 1. Intrinsic semiconductors - composed of only one kind of of electric current. material - It provides a framework for understanding the behavior of - pure semiconductors electrons in different types of materials (conductors, - silicon and germanium are some examples semiconductors, and insulators) based on their energy levels and These are also called undoped semiconductors or i-type how these levels are organized in a solid. semiconductors. 2. Extrinsic Semiconductors - are intrinsic semiconductors with other substances added to alter their properties — that is to say, they have been doped with another element. There are two types of extrinsic semiconductors that result from doping:  Other minerals containing aluminum are orthoclase 1.n-type for negative, from group V, such as phosphorus (KAlSi3O8 ), beryl (Be3Al2Si6O18), cryolite 2.p-type for positive, from group III, such as boron (Na3AlF6), and corundum (Al2O3 ). Considered as a precious metal until Hall developed a Extrinsic semiconductors method of Aluminum production N-Type Semiconductors - the semiconductor is doped with an element that has more valence electrons than the Preparation of Aluminum semiconductor material. For example, phosphorus (P) is Anhydrous aluminum oxide (Al2O3 or corundum) is reduced added to silicon. Silicon has 4 valence electrons, to aluminum by the Hall process. Phosphorus has 5 valence electrons. The key to the Hall process is the use of cryolite, or P-Type Semiconductors - the semiconductor is doped with an Na3AlF6 (melting point is 1000°C), as the solvent for element that has fewer valence electrons than the aluminum oxide (melting point is 2045°C). semiconductor material. For example, boron (B) is added to The mixture is electrolyzed to produce aluminum and silicon. Boron has 3 valence electrons while Silicon has 4 oxygen gas. Oxygen gas reacts with the carbon anodes to valence electrons. form carbon monoxide, which escapes as a gas. Recycling of Aluminum The Alkali and Alkaline Earth Metals Aluminum is one of the most recycled and most recyclable Alkali metals materials on the market today. Nearly 75% of all aluminum Chemical elements found in Group 1 of the periodic table. produced in the U.S. is still in use today. They appear silvery and can be cut with a plastic knife. Aluminum can be recycled directly back into itself over and The alkali metals include: lithium, sodium, potassium, over again in a true closed loop. rubidium, cesium, and francium. Recycling aluminum costs 95% less energy compared to Hydrogen is not technically an alkali metal since it rarely producing primary aluminum. exhibits similar behavior. The word "alkali" received its name from the Arabic word "al qali," meaning "from ashes", which since these elements react Transition Metals with water to form hydroxide ions, creating alkaline solutions Transition Metal – are elements in the d-block of the periodic (pH>7). table that have valence electrons in two shells Common properties of Alkali metals Transition elements are the elements that are found in The most electropositive or the least electronegative Groups 3-12 on the periodic table. elements Common oxidation state +1 Found dissolved in seawater due to geologic erosion of minerals All the discovered alkali metals occur in nature. These metals have a BCC structure with low packing efficiency. Low melting point Lithium - lightest known metal and has great chemical reactivity. Do not occur free in elemental form, are combined in halides, sulfates, carbonates and silicates. Alkaline Earth Metals Less electropositive and less reactive than Group IA Common oxidation state +2 Have much higher melting points than the alkali metals, harder metals than the Group 1A elements, but are soft Properties of Transition metal and lightweight compared to many of the transition Transition metals have similar properties, and some of these metals. properties are different from those of the metals in group 1. The chemistry of radium is not well established due to its Physical properties radioactivity. — they are good conductors of heat and electricity — they can be hammered or bent into shape easily Emerald is a variety of beryl, a mineral that contains the alkaline — they have high melting points (but mercury is a liquid at room earth metal beryllium. temperature) Beryllium only occurs naturally in combination with other — they are usually hard and tough elements in minerals. — they have high densities Chemical properties Aluminum The transition metals have the following chemical properties in Most abundant metal and the 3 rd most plentiful element common: in the Earth’s crust. — they are less reactive than alkali metals such as sodium Elemental form doesn’t occur in nature — they form colored ions of different charges Principal ore: Bauxite (Al2O3 H2O) — some are very unreactive (silver and gold) — many are used as catalysts Uses of transition metals Natural Polymer Transition metals have a wide range of uses. Their properties are Natural polymers have been around since life itself began. very similar but not identical. It is important to choose the right -occur in nature like plants, animals, or microorganisms and can be transition metal for the required purpose. extracted -water-based (water plays a crucial role in their structure, function, GOLD andinteractions) Natural Polymer Examples: cellulose, starch (and other complex carbohydrates), natural rubber, and DNA Synthetic Polymer SILVER Synthetic polymers (man made) were first developed in the early 20th century, and these polymers remarkably transformed our world as different materials can be created with properties that are ideal for different applications. COPPER Examples are nylon, polyethylene, polyester, Teflon, and epoxy. Currently, crude oil is the starting material for many synthetic polymers in plastics, pharmaceuticals, fabrics, and other carbon-based products. IRON Natural and Synthetic Polymers Iron is usually too soft to be used as the metal alone. It is usually mixed with small amounts of other elements to make steels, which are harder and stronger than iron, but easily shaped. However, iron and steel react slowly with water and air to produce rust. They must be protected with, for example, a layer of paint. CHROMIUM Homopolymer Polymers If a polymer is made up of only one type of monomer (e.g. Properties and Characterization of Polymers polyethylene), then it is known as homopolymer. Examples: Polymers Teflon ™ (polytetrafluoroethylene PTFE) Molecular compound that can be distinguished by a high poly-vinyl chloride (PVC) molar mass, ranging into thousands and even millions of mass and they are made up of many repeating units. The Chemistry of Polymer Molecules Polyethylene (PE) Ethylene (C2H4 ) is a gas at ambient temperature and pressure. Under appropriate conditions, ethylene gas will The root ‘mer’ means unit, and poly means many. Taken react and it will transform to polyethylene (PE) which is a together, the word polymer can be deconstructed as many solid polymeric material. units. Typically, ‘mer’ is referred to as a monomer. Ethylene is a stable molecule with two carbon atoms connected by a double bond. Polyethylene is made by the reaction of multiple ethylene molecules in the presence of catalyst. Polymer Molecules Polytetrafluoroethylene (PTFE) The molecules in polymers are large and because of their A synthetic polymer that is well-known for its remarkable size they are often referred to as macromolecules. chemical resistance, high-temperature stability, and non-stick The backbone of each of a carbon-chain polymer is a properties. string of carbon atoms and within each molecule, the Commonly known by the brand name Teflon. atoms are bound together by covalent bonds. Belongs to a family of polymers called the fluorocarbons.  Molecular Structure of Polymers A polymer that is highly crosslinked may Polymerization also be classified as a network polymer. Polymerization is the chemical process in which These materials have distinctive small molecules called monomers are chemically bonded mechanical and thermal properties; the to form long, repeating chains or networks, resulting in a epoxies, polyurethanes, and phenol polymer. formaldehyde belong to this group. Polymer structures Polymer structure Molecular weight and shape of a polymer is not the only basis of its physical characteristics, the difference in the structure of the molecular chains must also be considered. Common Types 1. Linear 2. Branched 3. Cross-linked 4. Network Common Polymeric Materials Polymer structure: Linear Linear polymers are those in which the Six Common Polymers repeating units are joined together end to Presently, there are more than 60,000 synthetic polymers end in single chains. These long chains are known, with this, six types of polymers account for roughly flexible where each circle represents a unit. 75% of those used in both Europe and the United States. The polymer chains are long and unbranched. There may be van der Waals and hydrogen bonding between the chains. Some of the common polymers that form with linear structures are polyethylene, polyvinyl chloride, polystyrene, polymethyl methacrylate (PMMA), nylon, and the fluorocarbons. Polymer structure: Branched The polymer chains have side chains or branches extending from the main chain which results in a lowering of the polymer density. Six Common Polymers For example, high-density polyethylene (HDPE) is primarily a linear polymer, whereas low density polyethylene (LDPE) contains short chain branches. Polymer structure: Cross-linked Adjacent linear chains are joined one to another at various positions by covalent bonds. The process of crosslinking is achieved either during synthesis (crosslinks form naturally while the polymer is being created) or by a nonreversible chemical 1. Polyethylene Terephthalate (PETE reaction (crosslinking happens after the or PET) polymer has been synthesized). Properties: transparent, strong, shatter resistant Many of the rubber elastic materials are Easily recyclable and widely accepted in Crosslinked. recycling programs. Polymer structure: Network Uses: soft-drink bottles, clear food Multifunctional monomers forming three containers, beverage glasses, fabrics or more active covalent bonds making three-dimensional networks. 2. High-Density Polyethylene stability limits of the polymer), irreversible degradation can occur. (HDPE) Irreversible degradation refers to the permanent deterioration or Properties: Strong, resistant to impact and breakdown of a material, substance, or system, where the changes chemicals. Similar to LDPE but more rigid, cannot be undone or reversed. tougher, and slightly more dense. Examples of common thermoplastic polymers are Uses: Opaque milk, juice, detergents, and PE, PS, PETE and PVC. shampoo bottles. Also used in water pipes, gas pipes, and fencing materials Thermosets Thermosets or thermosetting polymers are network polymers, 3. Polyvinyl chloride (PVC) once hardened through heat or chemical processes, these cannot be Properties: Can be rigid or flexible. Resistant to remelted or re-shaped. most chemicals, including oils, acids, and bases. Heating them again will degrade or burn the polymer instead of More difficult to recycle and can release toxic softening it. chemicals. As compared to thermoplastics, these thermoset polymers are generally harder, stronger and have better dimensional stability. Uses: Rigid: Plumbing pipe, house siding, charge cards, and hotel room keys. Examples of these thermosets are vulcanized rubbers, epoxies, Softened: Garden hoses, waterproof boots, phenolics, and some polyester resins. shower curtains, and electrical wiring. 4. Low Density Polyethylene (LDPE) Copolymers Properties: Soft, flexible and lightweight. Copolymers are polymers made from two or more different types Unreactive to acids and bases. of monomers that are chemically bonded together in a chain. It is possible that there are different sequencing arrangements Uses: Plastic bags, films, sheets, bubble along the polymer chains. wrap, toys, wire insulation Synthetic rubbers are usually copolymers. 5. Polypropylene (PP) Types of Copolymers Properties: Opaque, very tough, good weatherability. Has high melting point. Resistant to oils. Copolymers: Alternating Two different monomers alternate regularly Uses: Bottle caps. Yogurt, cream, and along the polymer chain. margarine containers. Carpeting, casual furniture, luggage 6. Polystyrene (PS) Properties: Crystal form is transparent, sparkling, somewhat brittle. Expandable form is lightweight. Difficult to recycle and Copolymers: Random can have a negative environmental impact. Two different units are randomly dispersed along the chain. Uses: Crystal form: Food wrap, CD cases, transparent cups. Expandable form: Foam cups, insulated containers, food packaging trays, and egg cartons. Thermoplastic and Thermosetting Polymers Copolymers: Block Thermoplastic and Thermosetting Polymers are two broad Identical repeat units are clustered in blocks categories of polymers, each with distinct properties and along the chain. applications based on their molecular structure and behavior when heated. Thermoplastics Thermoplastics or thermoplastic polymers Copolymers: Graft soften upon heating and later liquefy, then it Also called homopolymer, side branches of one hardens when cooled. type may be grafted to homopolymer main chains that are This process is reversible and can be repeated. composed of a different repeat unit. Commonly used in applications that require recycling or reshaping. However, when a thermoplastic is exposed to very high temperatures (beyond the thermal