Dr Helen Lang Dept p of Geology gy Geography g p y West Virginia University FALL 2010 GEOLOGY 284 MINERALOGY Mineralogy and the Development of Modern Ch i Chemistry A Bit of History Mineral processing and isolation of elements dates back to 2900 B C gold silver bronze copper tin alloy Alchemists developed techniques for purifying elements from minerals and studied mineral properties 1500 B C they hoped they could change h b base metals l into i gold ld Greeks Aristotle Theophrastus and others debated the nature of matter and came up with the concept of ATOMS smallest indivisible b ildi blocks building bl k off matter tt 400 300 400 300 B C BC History continued Then there was a big gap Philosophers theoreticians were isolated from practitioners ivory tower Utilityy of combiningg theoryy and practice p was finally realized at beginning of the Industrial Revolution Big advances in Chemistry and Mineralogy y began g in the 1800s finally Elements Simple uncombined chemical substances of which all compounds are made Concept of atoms revived Atoms consist of protons massive nuclear particles with charge neutrons massive nuclear particles with no charge electrons very low mass wave s particles with negative charge orbit nucleus in elusive orbitals variouslyy p shaped areas in which electrons have a high probability of being found d The Periodic Table It was recognized in about 1870 that if elements are arranged in order of increasing atomic weight chemical combining weight there is a periodic repetition of weight chemical properties This Thi led l d to t arrangementt off elements l t in i rows and columns And finally to the modern periodic table Sequence numbers are atomic numbers of protons of electrons atomic weight atomic number Filling Electron Orbitals Electrons occupy discrete energy levels each represented p byy different quantum numbers Orbitals are filled in order of i increasing i energy from f inner i to t outer shells Two electrons in each orbital with opposite spins Within each shell s orbitals are filled first p orbitals are filled next d orbitals next finally f orbitals are filled Fig 1 6 Perkins Orbitals arranged in order of increasing energy 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f Order of Filling of Electron Orbitals Xe For example Lead Pb Z 82 has the electron configuration 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p2 Some prefer to write it with all subshells of a given shell together 1s22s22p63s23p63d104s24p64d104f145s25p65d106s26p2 or Xe 6s24f145d106p2 See Periodic Table Properties of elements depend on which orbitals the valence outer electrons occupy Names of Groups of Elements LANL Periodic Table Wooden Periodic Table http www theodoregray com PeriodicTable index html tabletop a good book about chemistry Uncle Tungsten by Oliver Sacks Atomic and Molecular Weight Atomic weight of an atom A number of protons Z number of neutrons N Atomic weight of an element weighted average of atomic weights of all its isotopes different isotopes have different of neutrons neutrons properties depend mostly on protons which equals electrons In compounds molecules molecules including minerals elements are combined in proportion to their atomic weights g atomic weight atomic number Current WebElements Table printable i t bl http www webelements com nexus sites default files WEBELEM2 pdf The Fine Print atomic numbers atomic weights The last significant figure of each value is considered reliable to 1 exceptt where h a larger l uncertainty t i t is i given i in i parentheses th e g At Wt Mn 54 938049 0 000009 Elements for which the atomic weight is contained within square brackets have no stable nuclides and are represented by the element s more important isotopes Bonding Noble gases are particularly stable because the have they ha e completely completel filled electron shells Other elements try to fill their electron shells h ll by b stealing li or sharing h i electrons l this results in bonding When an atom gains one or more electrons it becomes a negatively charged anion When an atom loses one or more electrons it becomes a positively charged cation Types of Bonding Positively charged cations attract negatively charged g anions to form ionic bonds When electrons are shared the bonds are called covalent bonds Metallic bonds result when loosely bound valence outer electrons move freely throughthrough out the structure shared among many atoms not just two as in covalent Covalent Bonds occur among identical atoms or those close together g on the periodic p table are the strongest type of bonds therefore they form the hardest minerals which have the highest melting temperatures are directional di ti l the th angle l between b t bonds b d is i controlled by orientation of the shared orbitals bit l Ionic Bonds occurr among atoms that are far apart on the occ periodic table are weaker than covalent covalent but stronger than metallic bonds form minerals that are soluble in H2O O a polar solvent are non directional non directional anions and cations can be approximated as charged spheres that pack closely together in mineral structures Metallic Bonds are common in minerals that contain transition metals like Cu Fe Au Zn are the weakest of these bond types therefore metallic minerals are relatively soft Because electrons are free to move throughout the structure structure metallic minerals are good conductors of electricity Bonding in most minerals is not purely ionic ppurely y covalent or purely p y metallic IONIC halite corundum olivine amphibole galena di diamond d COVALENT sulfides nickelite sulfosalts molybdenite stibnite gold copper g pp silver METALLIC Earthh Scientist s E S i i Periodic P i di Table T bl A whole new approach pp Bruce Railsback U Georgia Geology 2003 http www gly uga edu railsback PT html Order of Filling of Electron Orbitals Xe For example Lead Pb Z 82 has the electron configuration 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p2 Some prefer to write it with all subshells of a given shell together 1s22s22p63s23p63d104s24p64d104f145s25p65d106s26p2 or Xe 6s24f145d106p2