2 7 2012 Chapter 3 Clicker 1 Atoms and Elements Isotopes and Ions Minerals and Rocks Chemistry Background A Review of Chemistry Atoms Learning Goals Atoms are composed of Protons Neutrons and Electrons The protons and neutrons are bound into the nucleus and contain all the mass The electrons orbit the nucleus The electrons interact with neighboring atoms and determine the chemistry Atoms and Elements The chemical properties of an element depend on the number and configuration of electrons i e the net electric charge The number of protons in the nucleus is known as the atomic number of the element Atomic numbers for natural elements range from 1 hydrogen to 92 for uranium A B C D No HS or College Chemistry High School Chemistry 1 semester College Chemistry 2 semesters College Chemistry Atoms Atoms are composed of Protons Neutrons and Electrons A proton has an electric charge of 1 and a rest mass of 1 67 x 10 24 gm A neutron has a charge of 0 and a rest mass of 1 67 x 10 24 gm about the same as a proton An electron has a charge of 1 and a rest mass of 9 11 x 10 28 gm much much less than a proton The electron mass is negligible relative to protons and neutrons Atomic Number The number of protons in the nucleus is the atomic number A neutral atom will have the same number of electrons as protons The elements are arranged by chemistry into the Periodic Table 1 2 7 2012 Ions and Valence Atoms with 1 2 3 or 4 outer electrons may lose them and form positive ions cations Atoms with 6 or 7 outer electrons may gain electrons to form negative ions anions The number of lost electrons is the valence The valence is thus the net electric charge The elements are arranged by chemistry into the Periodic Table Chemistry The chemical reactions an element is capable of is determined by the electron configuration Neutral atoms with complete outer shells don t enter chemical reactions Inert He Ne Ar Kr Xe The number of lost electrons net electric charge is the valence Ions and Valence Chemical Compounds Charge Denoted by Superscript Cations H 1 Na 1 Mg 2 Al 3 Si 4 Anions F 1 O 2 S 2 Elements occur in integer ratios to maintain charge balance H2 H2O SiO2 CaCO3 2 2 7 2012 Atomic Number and Ions The atomic number of an element is the number of protons positive charges in the nucleus H is atomic number 1 He 2 O 8 Ne 10 etc A neutral atom has the same number of electrons as protons Ions are charged atoms and have more or fewer electrons than protons Atomic Number and Ions Cations have fewer electrons than protons and a net positive charge Examples H Mg2 Al3 Si4 Anions have more electrons than protons and a net negative charge Examples F O2 Cl Atoms will gain or lose electrons to have a filled outer electron shell Isotopes Chemical Compounds Elements occur in integer ratios to maintain charge balance H2 H2O SiO2 CaCO3 Mass Number The mass numbers or isotopes of an element are denoted as preceding superscripts For example the stable isotopes of the element oxygen are denoted 18O 17O and 16O Oxygen has an atomic number of 8 eight protons The nucleus of 16O thus contains eight protons and eight neutrons The number of protons plus neutrons in the nucleus is known as the mass number of the atom Atoms of a given element atomic number may have differing numbers of neutrons Atoms of the same element with different mass numbers are known as isotopes Ions isotopes and molecules Ions are denoted with superscripts H 1 Na 1 Si 4 O 2 Isotopes are denoted with preceding superscripts 2H 3H mass number 14C 16O 18O 90Sr 137Cs 235U Molecules and compounds are denoted with subscripts H2 O2 SiO2 CaCO3 Mg2SiO4 3 2 7 2012 Atomic Weight A given element may have several stable isotopes The average mass number of an element is the atomic weight This is not an integer The atomic weight of H is 1 008 Nucleosynthesis The elements H He and minor amounts of Li were formed in the original Big Bang 13 7 BILLION YEASR AGO All heavier elements were formed from the primordial H and He by nuclear fusion and neutron capture reactions in stars The fusion reaction proceeds in steps in stars massive enough to undergo the full sequence Nucleosynthesis Large stars undergo successive fusion reactions until Fe is formed by direct fusion Heavier elements are formed by neutron capture The final fusion stage results in a supernova explosion Our solar system formed from the remnants of a supernova 4 2 7 2012 Minerals Learning Goals How is matter organized in the Earth What is a mineral What is A CRYSTAL periodic array How does matter self organize What is a rock Rock cycle Ice H2O Minerals A mineral is a naturally occurring homogeneous solid of definite chemical composition and ordered atomic arrangement that is usually formed by inorganic processes A Natural Crystalline Phase Minerals A mineral must occur naturally It must be chemically homogeneous down to the atomic level It must have a chemical formula e g SiO2 FeS2 It must have a defined crystal structure It must be inorganic not the result of biological processes alone Some Familiar Minerals Quartz SiO2 Pyrite FeS2 Calcite CaCO3 Gold Au Silver Ag Copper Cu Diamond C Graphite C Hydrothermal Gold K feldspar KAlSi3O8 Na feldspar NaAlSi3O8 Olivine Mg2SiO4 Garnet Mg3Al2Si3O12 Gypsum CaSO4 2H2O Apatite Ca5 PO4 3OH Ice H2O Halite NaCl Salt 5 2 7 2012 Calcite CaCO3 Halite NaCl Salt Occurrence Evaporites Salt Domes Uses Table salt De icing Nuclear waste host rock Ice H2O Quartz SiO2 Quartz SiO2 Mineral Properties We often display the crystal structure of minerals as polyhedra where the corners of the polyhedra represent oxygen and center is a cation like Si4 Hardness Mohs Scale Luster Color Shape Density 6 2 7 2012 Which of these is mineral Some Non Mineral Solids Obsidian Glass Opal Amorphous Coal Amorphous Wood Organic Amber Organic Which of these is mineral not a A Gold B Diamond C Obsidian D Graphite E Quartz Isomorphs not a A Gold B Diamond C Obsidian D Graphite E Quartz Polymorphs Same composition different structure Graphite Diamond C Quartz Tridymite Cristobalite Coesite Calcite Aragonite CaCO3 Pyrite Marcasite FeS2 Rocks are Composed of Minerals Same Structure Different Composition Olivine Mg2SiO4 Fe2SiO4 Calcite CaCO3 Rhodochrosite MnCO3 Apatite Ca5 PO4 3OH Ca5 PO4 3F 7 2 7 2012 A Rock is an Aggregate of Minerals Igneous Crystallized from melts Surface Volcanic Subsurface Intrusive Crust and Mantle Lithosphere and Asthenosphere Sedimentary Deposited from air and water on the surface Metamorphic
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