Atoms and Elements. Atoms: Learning Goals. Chapter 3. Atoms and Elements; Isotopes and Ions; Minerals and Rocks. Clicker 1. Chemistry Background?

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1 Chapter 3 Atoms Atoms and Elements; Isotopes and Ions; Minerals and Rocks A Review of Chemistry: What geochemistry tells us Clicker 1 Chemistry Background? A. No HS or College Chemistry B. High School Chemistry C. 1 semester College Chemistry D. 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 gm. A neutron has a charge of 0 and a rest mass of 1.67 x gm. (about the same as a proton). An electron has a charge of -1 and a rest mass of 9.11 x gm. (much, much less than a proton). [0.055%] The electron mass is negligible relative to protons and neutrons. 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. 1

2 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. (by atomic number) 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 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. 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 2

3 Chemical Compounds Elements occur in integer ratios to maintain charge balance H 2 hydrogen gas H 2 O water, ice SiO 2 quartz, cristobalite CaCO 3 calcite, aragonite Chemical Compounds Elements occur in integer ratios to maintain charge balance H 2 H 2 O SiO 2 CaCO 3 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. 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. Atomic Number and Ions Cations have fewer electrons than protons and a net positive charge. Examples: H +, Mg 2+, Al 3+, Si 4+ Anions have more electrons than protons and a net negative charge. Examples: F -, O 2-, Cl - Atoms will gain or lose electrons to have a filled outer electron shell. 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 18 O, 17O, and 16O. Oxygen has an atomic number of 8 (eight protons). The nucleus of 16O thus contains eight protons and eight neutrons. 3

4 Ions, isotopes, and molecules Ions are denoted with superscripts H +1, Na +1, Si +4, O -2 Isotopes are denoted with preceding superscripts (mass number) 2 H, 3 H, 14 C, 16 O, 18 O, 90 Sr, 137 Cs, 235 U Molecules and compounds are denoted with subscripts H 2, O 2, SiO 2, CaCO 3, Mg 2 SiO 4 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. (not the Big Bang) Our solar system formed from the remnants of a supernova. Atomic Weight Chondrule 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 mm Nucleosynthesis Earth differentiated into core and mantle. The elements H, He, and minor amounts of Li were formed in the original Big Bang. (13.7 BILLION YEARs 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. 4

5 Ice H 2 O 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? Minerals A mineral must occur naturally. It must be chemically homogeneous down to the atomic level It must have a chemical formula (e.g. SiO 2, FeS 2 ) It must have a defined crystal structure. It must be inorganic (not the result of biological processes alone). 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 Some Familiar Minerals Quartz (SiO 2 ) Pyrite (FeS 2 ) K-feldspar (KAlSi 3O 8) Na-feldspar (NaAlSi 3O 8) Calcite (CaCO 3 ) Olivine (Mg 2 SiO 4 ) Garnet (Mg Gold (Au) 3 Al 2 Si 3 O 12 ) Gypsum (CaSO 4 2H 2O) Silver (Ag) Apatite (Ca 5 (PO 4 ) 3 OH) Copper (Cu) Ice (H 2 O) Diamond (C) Halite (NaCl) (Salt) Graphite (C) 5

6 Hydrothermal Gold Ice H 2 O Halite NaCl (Salt) Quartz SiO 2 Occurrence: Evaporites, Salt Domes Uses: Table salt, De-icing, Nuclear waste host rock? Calcite CaCO 3 Quartz SiO 2 We often display the crystal structure of minerals as polyhedra where the corners of the polyhedra represent oxygen and center is a cation like Si 4+. 6

7 Mineral Properties Hardness (Mohs Scale) Luster Color Shape Density Which of these is not a mineral? A. Gold B. Diamond C.Obsidian D. Graphite E. Quartz 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 (CaCO 3 ) Pyrite - Marcasite (FeS 2 ) Which of these is not a mineral? A. Gold B. Diamond C. Obsidian D. Graphite E. Quartz Isomorphs Same Structure - Different Composition Olivine (Mg 2 SiO 4 ) (Fe 2 SiO 4 ) Calcite (CaCO 3 ) - Rhodochrosite (MnCO 3 ) Apatite (Ca 5 (PO 4 ) 3 OH) - (Ca 5 (PO 4 ) 3 F) 7

8 Rocks are Composed of Minerals Sedimentary Rocks form from weathering products of igneous and metamorphic rocks. Granite weathers to quartz, clay, and dissolved material. Water and air transport these on the surface and sort them by grain size. The different grain size fractions are deposited in different places. 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. Depositional Environments Crust and Mantle Lithosphere and Asthenosphere 8

9 1/20/2016 A Rock is an Aggregate of Minerals Igneous - Crystallized from melts Surface - Volcanic; Subsurface - Intrusive Black Rock Sedimentary - Deposited from air and water on the surface Metamorphic Recrystallized from pre-existing igneous or sedimentary rocks. Red Rock 9

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11 Assignment Grotzinger Chapter 4 Igneous Rocks Homework # 4 Atoms & Elements Terms Proton Neutron Electron Atomic weight Atomic number Mass Number Cation Anion Valence Isotope Fusion Fission Chondrule Clicker Question The term for any molten silicate material on or below the Earth s surface is: A. Granite B. Basalt C. Magma D. Pegmatite E. Lava Mineral & Rock Terms Mineral Crystal Hardness Luster Habit Density Isomorph Polymorph Clicker Question The most abundant element in the Earth is: A. Hydrogen B. Oxygen C. Magnesium D. Silicon E. Iron 11

12 Clicker Question The composition of the mantle is said to be: A. Ultramafic B. Mafic C. Intermediate D. Silicic E. Sedimentary 12