Department of Chemistry CHEM1020 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel:

CHEM1020/General Chemistry _________________________________________ Chapter 11. (L19)-Chemistry of Earth Today’s Outline …The earth’s surface …Earth’s lithosphere elemental composition of lithosphere inorganic substances, minerals organic substances …Silicates …Modified silicates

Chapter 11. (L19)-Chemistry of Earth The Earth surface …Structure of the earth core (Fe, Ni) mantle (silicates) crust (earth surface) …Earth surface lithosphere (primary silicates) pedosphere (secondary silicates) biosphere (biomolecules) atmosphere (gases) hydrosphere (water)

Chapter 11. (L19)-Chemistry of Earth Earth’s lithosphere …lithosphere physical feature: 35 km thick under continents 10 km thick under oceans …Elemental composition of lithosphere (percent by mass) O, 49.5%; Si, 25.7%; Al, 7.5% Fe, 4.7%; Ca, 3.4%; Na, 2.6% K, 2.4%; Mg, 1.9%; H, 0.9%; all others, 1.4% …Oxygen of the earth surface in hydrosphere in water in lithosphere in silicates in atmosphere as oxygen gas (O 2 )

Chapter 11. (L19)-Chemistry of Earth Earth’s lithosphere …lithosphere rocks igneous rocks sedimentary rocks metamorphic rocks rock cycle: the grand geochemical cycle rocks are composed of minerals, inorganic substances major mineral types: silicate minerals (metals with Si and O) carbonate minerals (metals with C and O) oxide minerals (metals with O) sulfide minerals (metals with S)

Chapter 11. (L19)-Chemistry of Earth Earth’s lithosphere I norganic substances minerals Organic substances coals natural gases petroleum oil shale

Chapter 11. (L19)-Chemistry of Earth Earth’s lithosphere Some nonsilicate minerals of economic importance Mineral TypeNameFormulaUse OxidehematiteFe 2 O 3 iron ore megnetiteFe 3 O 4 iron ore cornudumAl 2 O 3 gemstone SulfidegalenaPbSlead ore chalcopyriteCuFeS 2 Cu ore cinnabarHgSHg ore sphaleriteZnSZn ore CarbonatecalciteCaCO 3 cement lime

Chapter 11. (L19)-Chemistry of Earth Calcium carbonate: Limestone … Various calcium carbonates in nature marbles, seashells, eggshells, calcite, coral …Limestone (CaCO 3 ) Dissolution of limestone in nature CaCO 3 + CO 2 + H 2 O = Ca HCO 3 - chemistry of cave formation

Chapter 11. (L19)-Chemistry of Earth Silicates … Basic unit of silicates: an SiO 4 tetrahedron similarity between C and S C-H tetrahedron: the backbone of biosphere S-O tetrahedron: the backbone of lithosphere … an SiO 4 tetrahedron much like methane: CH 4 Si-O bond, 4 bonds of Si with 4 O angle: 109.5º

Chapter 11. (L19)-Chemistry of Earth Silicates Some common silicates (Table 11.3) Quartz: 3D silicates, pure silicon dioxide (SiO 2 ) sand, gems 3D-structure of SiO 4 tetrahedron Micas: sheet silicates SiO 4 tetrahedron arranged in 2D sheets the sheets are bound together by Al3 + Asbestos: linear SiO 4 tetrahedron arranged in chain two chains bound by oxygen to form double- chain structures; the double-chains bound by Mg 2+ fibrous, best known example: chrysotile, a magnesium silicate excellent insulator

Chapter 11. (L19)-Chemistry of Earth Silicates Hazardous effects of asbestos …inhalation of asbestos fibers can cause various lung diseases and cancers cigarettes can increase the risks significantly crocidolite is responsible for the hazardous effects chrysotile, 95% of the asbestos used in USA, perhaps appears to be less dangerous …Regulations that requires removal of asbestos from schools and other public buildings

Chapter 11. (L19)-Chemistry of Earth Modified silicates …Ceramics Inorganic materials made by heating clays or other mineral matter to a high temperature at which the particles of clays partially melt and fuse together natural clays: Al silicates bricks, tiles, cooking pots, water jugs, mugs, specialty materials: high heat-resistance ceramics (rocket nose cones, surface tile) super-conductance ceramics

Chapter 11. (L19)-Chemistry of Earth Modified silicates …Glass A non-crystalline solid, a mixture of sand (silicates), sodium carbonate (Na 2 CO 3 ), and limestone heated at high temperature to form a homogeneous liquid and after it cools, it becomes glass Properties: irregular arrangement of 3D SiO 4 tetrahedra by various kinds of chemical bonds; When heated, glass gradually softens The basic ingredients of glass can be used in different proportions and various kinds of metals oxides can replace one or more of the basic ingredients to form many special types of glass (Table 11.4) Optical fibers, pure threads of glass as thick as hair

Chapter 11. (L19)-Chemistry of Earth Modified silicates …Cement and concrete Cement: a complex mixture of calcium and aluminum silicates raw materials for cement: limestone and clay Concrete: cement mixed with sand and gravel Our understanding of the complex chemistry of cement still remains imperfect. Production of cement is highly energy- consuming roads destroy our green heritage

Chapter 11. (L19)-Chemistry of Earth Quiz Time Make up three or more quiz questions based on the content of this lecture together with the answer of four choices to each quiz question.