1Chapter 3Atoms and MineralsEarth MaterialsAtoms and Elements: Isotopes and IonsA Review of ChemistryAtoms•Atoms are composed of Protons, Neutrons and Electrons–A proton has an electric charge of +1 and a rest mass of 1.67 x 10-24gm. –A neutron has a charge of 0 and a rest mass of 1.67 x 10-24gm. (about the same as a proton). –An electron has a charge of -1 and a rest mass of 9.11 x 10-28gm. (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.2Ions and ValenceCharge Denoted by Superscript•Cations•H+1•Na+1•Mg+2•Al+3•Si+4•Anions•F-1•O-2•S-2Chemical Compounds•Elements occur in integer ratios to maintain charge balance•H2•H2O•SiO2•CaCO3Isotopes•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 isotopes1H, 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•H2is 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).3Minerals•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 PhaseMinerals•A mineral must occur naturally.•It must be chemically homogeneous down to the atomic level•It must have a chemical formula (egSiO2, 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 GoldOccurrence: Evaporites, Salt DomesUses: Table salt, De-icing, Nuclear waste host rock?Halite NaCl (Salt)Calcite CaCO34Ice H2OQuartz SiO2Quartz 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•DensitySome 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)5Isomorphs•Same Structure - Different Composition–Olivine (Mg2SiO4) (Fe2SiO4)–Calcite - Rhodochrosite (CaCO3) (MnCO3)–Apatite (Ca5(PO4)3OH) - (Ca5(PO4)3F)Rocks are Composed ofMineralsA 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.6Atoms & Elements Terms•Proton•Neutron•Electron•Atomic weight•Atomic number•Mass Number•Cation•Anion•Valence•Isotope•Fusion•Fission•Chondrule•Siderophile•Atmophile•Chalcophile•LithophileMineral & Rock
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