Chapter 3 Atoms and Minerals Earth Materials Atoms and Elements Isotopes and Ions A Review of 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 Atoms and Elements The chemical properties of an element depend on the number of protons i e the net electric charge of the nucleus The number of protons in the nucleus is known as the atomic number of the element Atomic numbers for natural element range from 1 hydrogen to 92 for uranium Chemistry The chemical reactions an element is capable of is determined by the electron configuration Atoms with complete outer shells don t enter chemical reactions Inert The number of lost electrons net electric charge is the valence 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 elements are arranged by chemistry into the Periodic Table Ions and Valence Charge Denoted by Superscript Cations H 1 Na 1 Mg 2 Al 3 Si 4 Anions F 1 O 2 S 2 Chemical Compounds Elements occur in integer ratios to maintain charge balance H2 H2O SiO2 CaCO3 Isotopes 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 Isotopes Mass number is denoted by a preceding superscript Hydrogen has isotopes 1H 2H 3H Helium is 3He 4He K has atomic number 19 How many neutrons are in the nucleus of 40K 40K 87Rb 235U 238U 232Th are naturally occurring radioactive isotopes Element Symbols subscripts and superscripts H2 is a molecule with 2 H atoms H1 is an ion of a H nucleus without its electron 2H is an atom of deuterium an isotope of Hydrogen 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 eg 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 K feldspar KAlSi3O8 Na feldspar NaAlSi3O8 Olivine Mg2SiO4 Garnet Mg3Al2Si3O12 Gypsum CaSO4 2H2O Apatite Ca5 PO4 3OH Ice H2O Halite NaCl Salt Hydrothermal Gold Halite NaCl Salt Occurrence Evaporites Salt Domes Uses Table salt De icing Nuclear waste host rock Calcite CaCO3 Ice H2O Quartz SiO2 Quartz SiO2 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 Mineral Properties Hardness Mohs Scale Luster Color Shape Density Some Non Mineral Solids Obsidian Glass Opal Amorphous Coal Amorphous Wood Organic Amber Organic Polymorphs Same composition different structure Graphite Diamond C Quartz Tridymite Cristobalite Coesite Calcite Aragonite CaCO3 Pyrite Marcasite FeS2 Isomorphs Same Structure Different Composition Olivine Mg2SiO4 Fe2SiO4 Calcite Rhodochrosite CaCO3 MnCO3 Apatite Ca5 PO4 3OH Ca5 PO4 3F Rocks are Composed of Minerals A Rock is an Aggregate of Minerals Igneous Crystallized from melts Surface Volcanic Subsurface Intrusive Sedimentary Deposited from air and water on the surface Metamorphic Recrystallized from pre existing igneous or sedimentary rocks Atoms Elements Terms Proton Neutron Electron Atomic weight Atomic number Mass Number Cation Anion Valence Isotope Fusion Fission Chondrule Siderophile Atmophile Chalcophile Lithophile Mineral Rock Terms Mineral Crystal Hardness Luster Habit Density Isomorph Polymorph Isotope Fusion Fission Chondrule Siderophile Atmophile Chalcophile Lithophile
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