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We saw that minerals are crystals, and We saw that minerals are crystals, and crystals are made of unit cells, crystals are made of unit cells, arrangements of atoms that, when stacked arrangements of atoms that, when stacked in 3 dimensions, form the complete crystalin 3 dimensions, form the complete crystal

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The edges of the unit cells, and therefore the crystal, are The edges of the unit cells, and therefore the crystal, are parallel to a system of crystal axes. Positive a is to the front, b parallel to a system of crystal axes. Positive a is to the front, b to the right, and c is up.to the right, and c is up.

The angle between b and c is called ,the angle between a and c is called , and the angle between a and b is called

The most pronounced zone is oriented vertically and an axis parallel to that zone is called c

Last TimeLast Time Six or seven crystal systems cover all possibilitiesSix or seven crystal systems cover all possibilities

Once c is selected, other axes are drawn parallel to a prominent face

=

Last TimeLast Time We also worked out a notation for the orientation of a crystal We also worked out a notation for the orientation of a crystal

face, Miller Indices, and learned how to plot them on a planeface, Miller Indices, and learned how to plot them on a plane

http://www.gly.uga.edu/Schroeder/geol6550/millerindices.html

Lecture 2 Lecture 2

Crystal ChemistryCrystal Chemistry

Part 1:Part 1:Composition of the Earth Composition of the Earth

Elements, and IonsElements, and Ions

Fe – 86%Fe – 86%S – 10%S – 10%Ni – 4%Ni – 4%

Chemical Layers of the EarthChemical Layers of the Earth

SiO2 – 45%SiO2 – 45%MgO – 37%MgO – 37%FeO – 8%FeO – 8%Al2O3 – 4%Al2O3 – 4%CaO – 3% CaO – 3% others – 3%others – 3%

Earth radius ~4000 miles, core about half way down (1800 miles)

Composition of the Earth’s CrustComposition of the Earth’s CrustWeight % Atom % Ionic Radius Volume %

O 46.60 62.55 1.40 93.8Si 27.72 21.22 0.42 0.9Al 8.13 6.47 0.51 0.5Fe 5.00 1.92 0.74 0.4Ca 3.63 1.94 0.99 1.0Na 2.83 2.64 0.97 1.3K 2.59 1.42 1.33 1.8Mg 2.09 1.84 0.66 0.3

Total 98.59 100.00 100.00

Most common silicates are from theseMost common silicates are from these

O alone = 94 vol. % of crustO alone = 94 vol. % of crust

Perhaps useful to think of the crust as a packed O array with interspersed Perhaps useful to think of the crust as a packed O array with interspersed metal cations in the interstices!metal cations in the interstices!

Analogy works for minerals too (they make up the crust)Analogy works for minerals too (they make up the crust)

Chemistry ReviewChemistry Review

Bohr model for the atomBohr model for the atom

1. Nucleus = p + n. (#protons = Atomic # identifies 1. Nucleus = p + n. (#protons = Atomic # identifies “element”) “element”)

(nucleus ~ all mass)(nucleus ~ all mass) Nucleus gives elements their properties Nucleus gives elements their properties

p + n (variable) p + n (variable) atomic weight (isotopes) atomic weight (isotopes)

At. Wt. is real # due to average of isotopesAt. Wt. is real # due to average of isotopes

2. Electrons e2. Electrons e-- spin around atom and give it its’ size spin around atom and give it its’ size

Atomic radii in the range 0.5-2.5 Atomic radii in the range 0.5-2.5 Å (1 (1 ångström = 1×101×10−10−10 m) m)

ee-- in special shells w/ particular energy levels- quantized in special shells w/ particular energy levels- quantized

Beryllium 1s2 2s2

The AtomThe Atom

The Bohr Model The Schrödinger ModelNucleus

- contains most of the weight (mass) of the atom- composed of positively charge particles (protons) and

neutrally charged particles (neutrons)Electron Shell

- insignificant mass- occupies space around the nucleus defining atomic

radius- controls chemical bonding behavior of atoms

Hydrogen Hydrogen

When atoms combine, the bonds formed are such that each atom is surrounded by 8 e-Octet Rule (Sienko & Plane p 55:

Electrons are in shells.

of Nesse

p-orbitals

s - orbitals

d-orbitals have up to 10 e-

1. Within each shell, electrons move in orbitals, volumes where an electron is most probably located.

2. The s orbitals fill a shell first, then the p-orbitals.

s orbitals have up to 2 e-p orbitals have up to 6 e-

First they occupy separate sub-orbitals, then when all are occupied they pair.

Filling up the Filling up the OrbitalsOrbitals

Order controlled by the energy of the orbitals

also 5s fills before 4d

Electronsoccupy orbitals in order of energy

level

Notice 4s fills before 3d because4s has a lower energy

Cl =1s22s22p63s23p5 =17 e-

Problem 1Problem 1

a. What is the electron configuration of a a. What is the electron configuration of a neutral atom of Calcium, element 20: neutral atom of Calcium, element 20:

Answer: Ca = 1sAnswer: Ca = 1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66 4s 4s22

b. What is the electron configuration of a b. What is the electron configuration of a neutral atom of Aluminum, element 13neutral atom of Aluminum, element 13

Answer: Answer: Al = 1sAl = 1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p11

Beyond Calcium, d-orbitals fill in complex ways, in order of orbital energy.

C. The order of increasing energy is1s 2s 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f Nesse p.41

Characteristics of an atom depend a lot on electron Characteristics of an atom depend a lot on electron configurationconfiguration

Atoms with a different numbers of protons & Atoms with a different numbers of protons & electrons, but with similar electron electrons, but with similar electron configurations, have similar propertiesconfigurations, have similar properties

This is especially true for the outermost shellThis is especially true for the outermost shell

Periodic TablePeriodic Table

Structure of the Periodic TableStructure of the Periodic Table# of Electrons in Outermost Shell Noble

Gases

Anions

--------------------Transition Transition Metals-Metals------------------

NOTE : Primary Shell being filled

Column number gives electrons in outermost shell; predicts Ion valence

metals

It is the outermost shell or It is the outermost shell or valencevalence electrons that electrons that predicts bonding behaviorpredicts bonding behavior

Similar outermost shell configurations Similar outermost shell configurations GroupsGroups in the in the Periodic Table columnsPeriodic Table columns

alkali metalsalkali metals (I) have one e (I) have one e-- in outer shell in outer shell

halogenshalogens (VII) have 7 e (VII) have 7 e--

inert gasesinert gases (VIII) have 8e (VIII) have 8e-- ... filled s & p ... filled s & p

Problem 2Problem 2

A neutral atom of Calcium has the A neutral atom of Calcium has the electronic configuration of: electronic configuration of:

1s2 2s2 2p6 3s2 3p6 4s21s2 2s2 2p6 3s2 3p6 4s2Question: Which are the valence Question: Which are the valence

electrons?electrons?Answer: the 4s2. The Calcium can lose Answer: the 4s2. The Calcium can lose

these rather easily, yielding a Cathese rather easily, yielding a Ca++++ ion. ion.

Atoms of Geologic ImportanceAtoms of Geologic ImportanceImportant elements are abundant

Elements and IsotopesElements and Isotopes Elements are defined by the number of protons in the Elements are defined by the number of protons in the

nucleus (atomic number). nucleus (atomic number). In a stable element (zero charge), the number of electrons is In a stable element (zero charge), the number of electrons is

equal to the number of protonsequal to the number of protons The various isotopes of a particular element are defined by The various isotopes of a particular element are defined by

the total number of neutrons in addition to the number of the total number of neutrons in addition to the number of protons in the nucleus (isotopic number). protons in the nucleus (isotopic number).

Various elements can have multiple (2-38) stable isotopes, Various elements can have multiple (2-38) stable isotopes, some of which are unstable (radioactive)some of which are unstable (radioactive)

Isotopes of a particular element have the same chemical Isotopes of a particular element have the same chemical properties, but different masses. properties, but different masses.

Ions and Valence StatesIons and Valence States

CationsCations – “positive ion” one or more electrons removed – “positive ion” one or more electrons removed from outer shell, often a metal, e.g. Nafrom outer shell, often a metal, e.g. Na++, Fe, Fe++++, Fe, Fe++++++, Mg, Mg++

++, Ca, Ca++++, S, S+6+6

AnionsAnions – “negative ion” one or more electrons added to – “negative ion” one or more electrons added to outer shell; always a non-metal element, example Clouter shell; always a non-metal element, example Cl--, S, S----

Valence StateValence State (or oxidation state) – the common ionic (or oxidation state) – the common ionic configurations of a particular element -determined by configurations of a particular element -determined by how many electrons are typically stripped or added to how many electrons are typically stripped or added to form an ionform an ion

Elements can attain an inert gas configuration (octet rule)Elements can attain an inert gas configuration (octet rule)

Valence States of Ions and Anionic Valence States of Ions and Anionic Groups common to Rock-forming Groups common to Rock-forming

MineralsMineralsCationsCations – – metalsmetals, ,

transition metals, transition metals, semiconductors and semiconductors and nonmetalsnonmetals that have that have lost electronslost electrons

AnionsAnions – – nonmetals nonmetals with extra electronswith extra electrons

Anionic GroupsAnionic Groups tightly bound ionic tightly bound ionic complexes with complexes with net negative net negative charge, SOcharge, SO44

-2-2,, COCO33

-2-2, NO, NO33--, SiO, SiO44

-4-4, , POPO44

-3-3

+1 +2 +3 +4 +5 +6 +7

-2 -1

-----------------Transition Metals---------------

Problem 3Problem 3

A neutral atom of Calcium has the A neutral atom of Calcium has the electronic configuration of: electronic configuration of:

1s2 2s2 2p6 3s2 3p6 4s21s2 2s2 2p6 3s2 3p6 4s2a. What is the electron configuration for a. What is the electron configuration for

the Cathe Ca++++ ion? ion?

b. How many electrons does Ca++ have in b. How many electrons does Ca++ have in its outermost shell?its outermost shell?

Alkalis have one extra electron, can Alkalis have one extra electron, can lose it to attain outer octet. lose it to attain outer octet. This results in This results in an an ionion with a +1 with a +1 valence, Navalence, Na++

Group II alkaline earths will lose 2 eGroup II alkaline earths will lose 2 e-- +2 Become a +2 valence ion, Ca+2 Become a +2 valence ion, Ca++++

Halogens will capture an eHalogens will capture an e-- inert gas inert gas configuration. configuration. -1 valence ion. Cl -1 valence ion. Cl--

Properties derived from outer eProperties derived from outer e--

Ionization potential Ionization potential energy required to energy required to remove the least tightly bound electronremove the least tightly bound electron

Electron affinity Electron affinity energy given up as an energy given up as an electron is added to an elementelectron is added to an element

Electronegativity Electronegativity quantifies the quantifies the tendency of an element to attract a shared tendency of an element to attract a shared electron when bonded to another element.electron when bonded to another element.

In general, first ionization potential, electron In general, first ionization potential, electron affinity, and electronegativities increase from left affinity, and electronegativities increase from left to right across the periodic table, and to a lesser to right across the periodic table, and to a lesser degree from bottom to top.degree from bottom to top.

Ionic vs. CovalentIonic vs. CovalentElements on the right and top of the periodic Elements on the right and top of the periodic

table draw electrons stronglytable draw electrons stronglyBonds between atoms from opposite ends Bonds between atoms from opposite ends

more ionic, diatomics are 100% covalentmore ionic, diatomics are 100% covalentBond strength Bond strength Covalent>Ionic>metallic Covalent>Ionic>metallic

Affects hardness, melting T, solubilityAffects hardness, melting T, solubilityBond type affects geometry of how ions are Bond type affects geometry of how ions are

arrangedarrangedMore ionic vs. covalent = higher symmetryMore ionic vs. covalent = higher symmetry

Atomic RadiusAtomic RadiusA function partly of shielding, size is critical A function partly of shielding, size is critical

in thinking about substitution of ions, in thinking about substitution of ions, diffusion, and in coordination numbersdiffusion, and in coordination numbers

Again: Outer Electron stuffAgain: Outer Electron stuff

Ionization PotentialIonization Potential – measure of the energy – measure of the energy necessary to strip an element of its necessary to strip an element of its outermost electron. Low in alkali metals, outermost electron. Low in alkali metals, e.g. Sodium Na => Na+ e.g. Sodium Na => Na+

ElectronegativityElectronegativity – measure strength with – measure strength with which a nucleus attracts electrons to its which a nucleus attracts electrons to its outer shell. High in the abundant element outer shell. High in the abundant element oxygen.oxygen.

Electronegativity (e-neg)Electronegativity (e-neg)

MeMetatalsls w/ e-neg < 1.9 thus lose ew/ e-neg < 1.9 thus lose e-- and and cationscations

NonNonmetalsmetals > 2.1> 2.1 thus gain ethus gain e-- and and anionsanions

MetalloidsMetalloids intermediate intermediate (B, Si, Ge, As, Sb, Te, Po)(B, Si, Ge, As, Sb, Te, Po)

Small Cations

Medium Cations

Large Cations

Huge Cation

1.Cations are smaller than their neutral counterpart. Electrons lost, so outer electron cloud is smaller.

2.Anions are much larger than their neutral counterpart. Electrons gained, so outer electron cloud is larger.

(Oxide Ion)

Ferric Ion

Ferrous Ion

Note SizesHuge K+ needsa large spacebetween anions

Problem 4Problem 4

Write down the common cations of Silicon Write down the common cations of Silicon Si, Aluminum Al, Iron Fe (there are two, Si, Aluminum Al, Iron Fe (there are two, ferrous and ferric Iron), Magnesium Mg, ferrous and ferric Iron), Magnesium Mg, Sodium Na, Calcium Ca, Potassium K, Sodium Na, Calcium Ca, Potassium K, and Sulfur.and Sulfur.

Write down the common anions of Write down the common anions of Oxygen, Chlorine, and Sulfur.Oxygen, Chlorine, and Sulfur.

The sizes vary with Coordination,the number of touching neighbors

Unit Cell

The Cations fill the space available between the Anions

Next LectureNext Lecture

Bonding and Ionic RadiiBonding and Ionic Radii