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Chapter 3  Elements of Crystal Chemistry

I.                    Chemical Composition of the Earth’s Crust

a.       Chemical Composition of the Earth’s Crust

b.      Crust,

                                                               i.      Sedimentary (thin layer) over igneous and Met rock, basalt and granite

                                                             ii.      Upper ten miles = 95% igneous, 4% shale, .75% sandstone, and .25% limestone

                                                            iii.      Mohorovicic discontinuity or the Moho is the boundary

c.       Mantle

                                                               i.      Stony meteorites

                                                             ii.      Upper mantle, transition zone and lower mantle

d.      Core

                                                               i.      Iron/nickel

e.       8 elements make up of 99 weight percent of crust, Oxygen #1

II.                 Atom

a.       Nucleus

                                                               i.      Protons – atomic number = Z

                                                             ii.      Neutrons –

1.      with protons = Atomic Mass

2.      differing numbers of neutrons are called isotopes

b.      Electrons

c.       Bohr Model in 1913

                                                               i.      Electrons flow in fixed energy levels known as K,L,M,N etc.

d.      Schrödinger Model

                                                               i.      Based on quantum mechanics

III.               Ion = protons and electrons are not equal

a.       Cation is an atom – electron =positive

b.      Anion is atom + electron = negative

c.       Electron donors are metals, left hand of the table

d.      Electron acceptors are the nonmetals, right hand part of the table

e.       Energy is always involved

IV.              Bonding

a.       Ionic Bonds – Exchange of electrons

b.      Covalent bond – sharing of electrons, electron does double duty, ex CL

                                                               i.      This is the toughest bond

                                                             ii.      Carbon living building block

c.       Metallic Bond

                                                               i.      Free flowing electrons, allows plasticity, tenacity, ductility and conductivity and low hardness

                                                             ii.      Non valence electrons

d.      Van der Waals Bond or forces

                                                               i.      Very weak

                                                             ii.      Molecules of negative poles and positive poles

                                                            iii.      Solid gasses

e.       Hydrogen Bond

                                                               i.      Electrostatic bond between a positively charged hydrogen ion and a negatively charged ion such as O or N

                                                             ii.      Hydrogen transfers its electron to neg ion in ionic bonding, the remaining proton of hydrogen nucleus becomes positive thus creating a polarization of the molecule like H2O

                                                            iii.      Ice is a good example

                                                           iv.      This gives water its unique properties.

V.                 Coordination of ions

a.       Based on size

b.      Packing arrangements – see page 72

c.       Pauling’s Rules 1-4 maximize cation-anion attraction

                                                               i.      A polyhedron of anions is formed about each cation

                                                             ii.      Electrostatic valency principle  -  In a crystal structure the total strength of the valency bonds that reach an anion from all the neighboring cations is equal to the charge fo the anion.

                                                            iii.      The existence of edges and faces, common to two anion polyhedra in a coordinated structure decreases its stability.

                                                           iv.      In a crystal containing different cations, those of high valency and small coordination number tend not to share polyhedral elements with each other

                                                             v.      Principle of parsimony – in complex composition, ions may occupy same sites with a single constituent.

VI.              Crystal Structure

a.       Crystal Structures

                                                               i.      Axis are xyz or a1 a2 a3 and c

                                                             ii.      Faces are a b and c.

                                                            iii.      Tetrahedrons up or down

b.      Isostructuralism

                                                               i.      Same structure type

                                                             ii.      Used to show relationships in mineral groups

VII.            Examples

a.       NaCL structure see book

b.      Silicates

                                                               i.      Single

                                                             ii.      Doubles

                                                            iii.      Ring

                                                           iv.      Chain

                                                             v.      Double chain

                                                           vi.      Sheet

                                                          vii.      Framework

VIII.         Graphing mineral composition

a.       Based on percents,

b.      Tertiary diagram