[email protected] engr-45_lec-02_atomicbonding.ppt 1 bruce mayer, pe engineering-45:...
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[email protected] • ENGR-45_Lec-02_AtomicBonding.ppt1
Bruce Mayer, PE Engineering-45: Materials of Engineering
Bruce Mayer, PERegistered Electrical & Mechanical Engineer
Engineering 45
Atomic StructureAtomic Structureandand
InterAtomic InterAtomic BondingBonding
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Learning GoalsLearning Goals
Understand the Sources/Causes of Atom-Level Bonding
Understand The Number & Types of Bonding
Determine Which properties May be inferred from bonding trends
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Bruce Mayer, PE Engineering-45: Materials of Engineering
The Nuclear AtomThe Nuclear Atom
Current Best Model of the Atomic Structure• A Small & Dense
NUCLEUS surrounded by an Electronic Cloud
Nucleus Composition → Two Constituents• PROTONS → POSITIVE Electronic Charge
• NEUTRONS → UNcharged
Electronic Cloud Composed of NEGATIVELY Charged ELECTRONS
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Atomic FactsAtomic Facts
ELEMENTS are Defined by the Atomic Number, Z• Z Number of Protons
– For NATURALLY Occurring Elements Z Ranges from 1 (H) to 92 (U)
By the Electronic Neutrality Requirement • [No. Protons] = [No. Electrons]
Electronic Charge = 1.6x10-19 Amp•sec• Note: 1 A•s = 1 Coulomb (C)
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Atomic Facts contAtomic Facts cont
Since The No. of NEUTRONSAre not Constrained by ChargeNeutrality, Then The SAME Element May Have Different No.s of Nuetrons, N • Elemental Forms with Different Neutron
Counts are Called ISOTOPES– e.g,; Consider Oxygen with Z = 8
O Isotope Neutrons, N Abundance16O 16-8 = 8 99.7620%17O 17-8 = 9 0.0383%18O 18-8 = 10 0.2001% h
ttp://ie.lbl.gov/education/isotopes.htm
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Recall the Periodic TableRecall the Periodic Table
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Atomic Facts cont.2Atomic Facts cont.2
Atomic Weight/Mass, A Weighted Average of NaturallyOccurring Isotopes
SubAtomic Particle Masses • Electron, e- = 9.11x10-31 kg
• Proton, p+ , and Neutron, n = 16 700x10-31 kg
Since Mp+ & Mn >> Me-
• Then A (Z+N)Mn
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Bruce Mayer, PE Engineering-45: Materials of Engineering
amu & gMolamu & gMol
By SI DEFINITION 12.00000... grams of 12C contains ONE gram-Mol of Carbon• 1 Mol of Any element Contains 6.023x1023
Protons and/or Electrons– 6.023x1023 Avagrado’s Number
Atomic Mass Unit, amu• 1 amu/atom = 1 g/mol
– e.g.; Atomic Wt of Niobium = 92.91 amu/atom = 92.91 g/mol
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Atomic ReactionsAtomic Reactions
Nuclear Reaction• Change in the Number of Neutrons, N, or
Protons, Z, in an Atom– Remember, Changing Z Changes the
ELEMENT TYPEe.g., a Nuclear Reaction can Change LEAD to GOLD
Chemical Reaction• Exchange or ReArrangement of
ELECTRONS– VAST Majority of Matl Sci Done with Chem Rcns
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Electron Behavior → QuantaElectron Behavior → Quanta
Electronic Behavior Governed by Quantum (Energy) Mechanics (QE)• QE Studied in Advanced
Physics/Chemistry, and Some Branches of Engineering
Basic Principle of QE as Applied to Materials Science• Electrons can have ONLY DISCRETE
Quantities (quanta) of Energy– i.e., e- Energy Levels are QUANTIZED
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Bohr AtomBohr Atom 1st
QuantumModel• Electrons Revolve Around
Nucleus at Discrete EnergyLevels Called Orbitals
A Refined Model Based on Wave Mechanics• e- Treated as Both a WAVE
and a PARTICLE– Position is Determined STATISTICALLY,
not Physically
orbital electrons: n = principal quantum number
n=3 2 1
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Atom: Shells & ValenceAtom: Shells & Valence
Nucleus
Proton
Neutron
INNER Shell Electron
VALENCEElectron
VALENCEShell/Orbit
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Atom Structure - ValenceAtom Structure - Valence Only the electrons
(e-) in the OUTERmost electron shell can participate in CHEMICAL Reactions
Adding or Removing an e- creates a CHARGED Atom Called an ION
Valence e- Behavior Governs the Atom’s Ability to combine with other elements
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Valence eValence e-- Importance Importance
A CHEMICAL reaction is the restructuring of the VALENCE Electrons in two or more Elements
Valence electron structure determines all of the following properties
Composition Electrical
Thermal Optical
[email protected] • ENGR-45_Lec-02_AtomicBonding.ppt15
Bruce Mayer, PE Engineering-45: Materials of Engineering
Electron Configuration of AtomsElectron Configuration of Atoms Four QUANTUM
NUMBERS Describe the Electronic Configuration of Atoms
1st
Shell2nd
Sub-shell3rd
# ElectronsPer Sub-shell
4th
Spin
1
2
3
n
dp
s
s
sp
1062
62
2
M
L
K
• 3rd Quantum No. Describes the Number of VALENCE Electrons
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Electron Energy StatesElectron Energy States e- have DISCRETE energy states; tend to
occupy LOWEST available energy state.
1s
2s2p
K-shell n = 1
L-shell n = 2
3s3p M-shell n = 3
3d
4s
4p4d
Energy
N-shell n = 4
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Shell Filling RulesShell Filling Rules
Following Quantum Mechanics1. Electrons Fill Shells/Orbitals to MINIMIZE
the Overall Atom Energy
2. Only TWO e- can Occupy a Single Orbital– Must Have OPPOSITE “SPINS”: ↑ and ↓
3. Electrons Stay as Widely Separated in physical space as Possible
– Favors EMPTY Orbitals as opposed to Half-Filled Orbitals of the SAME Energy
Leads to apparently “NONsequential” Filling; e.g. Ca (20) and Sc (21)
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Electronic ConfigurationElectronic Configuration
42622 33221 pspssS Principal
Quantum No. SubShell ElectronsPer SubShell
Number of VALENCE Electrons
The Normal Fill Sequence• 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p
→ 5s → 6s → 4f → 5d → 6p → 7s → 5f →6d → 7p
For a Given Shell Structure We can Write a ShortHand for an Element’s Electronic Structure; e.g., Sulfur
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Stable Electron ConfigurationsStable Electron Configurations Stable Electron Configurations
• Have COMPLETE s & p SubShells– i.e., The VALENCE SubShell is FULL
• Are VERY Unreactive
Z Element Configuration
2 He 1s2
10 Ne 1s22s22p6
18 Ar 1s22s22p63s23p6
36 Kr 1s22s22p63s23p63d104s24p6
“OCTET”RULE:Ns2Np6
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Bruce Mayer, PE Engineering-45: Materials of Engineering
PeriodicPeriodicTableTable
Structure Structure
n=1 (1sn=1 (1s11))n=2 (2sn=2 (2s11))n=3 (3sn=3 (3s11))n=4 (4sn=4 (4s11))R
ow
s(v
ale
nce s
hells)
Columns(valence electron structure)
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Periodic Table Structure cont.Periodic Table Structure cont. Rows: Same OUTER Shell (Primary Quantum No.) Column: SAME Number Of Valence Electrons
Similar Properties Trends: Atomic Radii, Electronegativity (tendency
to acquire electrons)
META
LS
NO
NM
ETA
LS
Radii
More ElectroNegLess ElectroNeg
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Periodic Table StructurePeriodic Table Structure Organized by Quantum No., Valence
(or Group), and SubShell
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Metals, SemiMetals, NonMetalsMetals, SemiMetals, NonMetalss p
d
f
Qu
antu
m N
o.
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Metals, SemiMetals, NonMetalsMetals, SemiMetals, NonMetals METALS
• Solid at Room Temperature– Except Hg
• Maleable & Ductile
• Conduct Electricity
NonMetals (17)• Poor Heat
Conductors
• Brittle and Fracture Easily
SemiMetals• 6 or 7 (Astatine
is the Wobbler)
• Have Some Metal-Like Properties– Solids at Rm Temp
– Can Conduct Electricity
• Have Some NonMetal-Like Props– Hard & Brittle
At
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Refined Shell Model for NitrogenRefined Shell Model for Nitrogen
Valence SHELL(L or 2)
Valence SUBShell(2p)
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Molecular BondingMolecular Bonding
Molecules (2+ units of SAME atom) and Compounds (2+ DIFFERENT atoms) are Formed by CHEMICAL Bonding
CHEMICAL Bonds Result from ELECTRON Configuration Rearrangement• STRONG Bonds → Ionic, Metallic,
Covalent
• WEAK Bonds → Van Der Waals – DiPole, Polar, H-Bond
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Bond-Energy Bond-Energy CurveCurve
Balance Between Atoms’ REPULSIVE and ATTRACTIVE Forces• ZERO Net Force
• LOWEST System Energy
Bond Distance Equilibrium InterAtomic Distance, or LATTICE Constant
Bond STRENGTH ↑• Melting Temperature ↑
• Stiffness ↑
too close → Repulsion
too far → Attaction
“just right”:r0 - equilibrium bond distance
Forc
eEn
erg
y
Min U
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Ionic BondingIonic Bonding Ion An Atom That Has Gained/Lost e-(s)
• Resulting Ion has +/- CHARGE
Ionic Bonding Ocurrs Between + & - Ions• Requires Electron TRANSFER; e.g. NaCl
Na (metal) Unstable
1s22s22p63s1
Na (cation) Stable
1s22s22p6
Cl (nonmetal) Unstable
1s22s22p63s23p5
electron
Coulombic Attraction
Cl (anion) Stable
1s22s22p63s23p6
+ -
X
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Ionic Bonding ExamplesIonic Bonding Examples Dominant Bonding Type for CERAMICS
Give up electrons Acquire electrons
He -
Ne -
Ar -
Kr -
Xe -
Rn -
F 4.0
Cl 3.0
Br 2.8
I 2.5
At 2.2
Li 1.0
Na 0.9
K 0.8
Rb 0.8
Cs 0.7
Fr 0.7
H 2.1
Be 1.5
Mg 1.2
Ca 1.0
Sr 1.0
Ba 0.9
Ra 0.9
Ti 1.5
Cr 1.6
Fe 1.8
Ni 1.8
Zn 1.8
As 2.0
CsCl
MgO
CaF2
NaCl
O 3.5
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Bruce Mayer, PE Engineering-45: Materials of Engineering
CoValent BondingCoValent Bonding Requires SHARED
Electrons (Co-Valent)
Example is CH4 (methane)
• C: has 4 valence e-’s, needs 4 more
• H: has 1 valence e-, needs 1 more
Characteristics• If A compound, Then
Electronegativities are comparable
• ≥4 valence e-’s
Cl2
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Bruce Mayer, PE Engineering-45: Materials of Engineering
CoValent Bonding ExamplesCoValent Bonding Examples NonMetallic Elemental
Molecules; e.g. F2
Hydrogen Compounds; e.g., HF, HNO3
Elemental Solids; e.g., C, Si, Ge
Near Group-IVA Solid Compounds; e.g. GaAs
He -
Ne -
Ar -
Kr -
Xe -
Rn -
F 4.0
Cl 3.0
Br 2.8
I 2.5
At 2.2
Li 1.0
Na 0.9
K 0.8
Rb 0.8
Cs 0.7
Fr 0.7
H 2.1
Be 1.5
Mg 1.2
Ca 1.0
Sr 1.0
Ba 0.9
Ra 0.9
Ti 1.5
Cr 1.6
Fe 1.8
Ni 1.8
Zn 1.8
As 2.0
SiC
C(diamond)
H2O
C 2.5
H2
Cl2
F2
Si 1.8
Ga 1.6
GaAs
Ge 1.8
O 2.0
col IV
A
Sn 1.8Pb 1.8
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Mixed Ionic+Covalent BondingMixed Ionic+Covalent Bonding
Many Compounds Exhibit Ionic-Covalent Mixed Bonding
1
%1001 Ionic-% 4
2
BA XX
e
• where XA & XB are Pauling ElectroNegativities
Example MgO: XMg = 1.3, XO = 3.5
%2.701
%1001 Ionic-% 4
5.33.1 2
e
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Metallic BondsMetallic Bonds
Ne config
Electrons Shared By All Atoms• “sea of electrons” around
“ion cores”
Ion Cores• Atoms Give Up Valence-e-
to the “sea”, leaving remaining Atoms with a Positive Ionic Charge– The Ion contains the Large
& Heavy Nucleus and is thus FIXED in Space
Generally Applies to Electro-Positive Elements• e.g.; Transition Metals such
as Ti, Ni, Zn, Cu
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Secondary BondingSecondary Bonding Arises from Atomic or
Molecular DIPOLES What’s a DiPole?
• Separation of the + & - Charge-Centers– Generates an
ELECTRIC Field within the Entity
Fluctuating DiPoles• Charge Centers Due to
SHORT-LIVED Charge Asymmentry
E-Field
asymmetric electron clouds
+ - + -secondary bonding
Liquifying Force for Electrically Neutral and Symetrical Molecules such as H2, N2
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Secondary Bonding cont.Secondary Bonding cont. Ionic Bonding in some
Molecules results in a PERMANENT Dipole
The +/- End of These Polar Molecules can Then Attract the -/+ Ends of Other Polar Molecules
General Case + - secondary bonding + -
H Cl H Clsecondary bonding
secondary bonding
e.g.; HCl Liquid
e.g.; PolymerSolid
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Secondary Bonding, H BondSecondary Bonding, H Bond Recall that H has in
Only a Single Proton and Electron • NO Neutrons
When H forms an Ionic Bond, it Gives Up (for the most part) the e-
• This Leaves the Hydrogen’s p+ Ionic Core Unscreened by any e-’s
• This Forms a Molecule with a POSITIVE (and Negative) end
This Proton-Induced Dipole is quite Strong and Can Lead to relatively powerful Dipole Bonding• Classic Example = H2O
to Form Liquid or Solid
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Summary: Chemical BondingSummary: Chemical Bonding
Bond Type Bond Energy Notes
Ionic LargeNonDirectionale.g.; Ceramics
Covalent
Variable• Large =>Diamond• Small => Bismuth
Directionale.g.: SemiConductors, Ceramics,
Polymer-Chains
Metallic
Variable• Large => Tungsten• Small => Mercury
NonDirectionale.g.; Metals
Secondary Smallest
DirectionalInterchain (PolyMer)
InterMolecular (Liq Water)
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Properties From Bonding: TProperties From Bonding: TMeltMelt
Bond Length Melting Temperature, TM
Bond Energy, E0
General Relationship:|E0|↑ TM ↑
r
larger TM
smaller TM
Energy (r)
ro
r
Eo=
“bond energy”
Energy (r)
ro r
unstretched length
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Properties From Bonding: EProperties From Bonding: E Modulus of Elasticity
Defined Modulus of Elasticity
Curvature of E vs r curve
Mathematically, E
General Relationship:|E0|↑ E ↑L F
Ao = E
Lo
Elastic modulus
r
larger E
Smaller E
Energy
ro unstretched length
cross sectional area Ao
L
length, Lo
F
undeformed
deformed
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Properties From Bonding: Properties From Bonding: Coefficient of Thermal
Expansion, , Defined ~symmetry at r0
Mathematically,
General Relationship:|E0|↑ ↑
r
Larger
Smaller
Energy
ro L
length, Lo
unheated, T1
heated, T2
= (T2 -T1)LLo
coeff. thermal expansion
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Summary: Primary BondsSummary: Primary Bonds
Ceramics(Ionic & covalent bonding):
Metals(Metallic bonding):
Polymers(Covalent & Secondary):
secondary bonding
Large bond energylarge Tm
large Esmall
Variable bond energymoderate Tm
moderate Emoderate
Directional PropertiesSecondary bonding dominates
small Tm
small Elarge
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Bruce Mayer, PE Engineering-45: Materials of Engineering
All Done for TodayAll Done for Today
α Superimposed
On PeriodicTable
GALLUIUM is the Tall Yellow one SODIUM is th Tall Blue one
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Bruce Mayer, PE Engineering-45: Materials of Engineering
WhiteBoard Work – P2.13WhiteBoard Work – P2.13
K+ & O2-
dipotassium oxide = K2Or0 = 1.5 nm
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Bruce Mayer, PE Engineering-45: Materials of Engineering
Problem TutorialProblem Tutorial
Let’s WorkText Problem
2.14
CalcuimOxide →
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Bruce Mayer, PE Engineering-45: Materials of Engineering
P2.13P2.13
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Bruce Mayer, PE Engineering-45: Materials of Engineering
P2.13P2.13
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Bruce Mayer, PE Engineering-45: Materials of Engineering
P2.13P2.13
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Bruce Mayer, PE Engineering-45: Materials of Engineering
P2.14P2.14
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Bruce Mayer, PE Engineering-45: Materials of Engineering
P2.14
P2.14
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Bruce Mayer, PE Engineering-45: Materials of Engineering
P2.15
P2.15
% Program E45_Prob_2_15_1101.m:
% Plot EA and ER vs r * Verify r0 numerically
% Bruce Mayer, PE • ENGR45 • 24Jan11
%% Calc r0 numerically using anonymous fcn for En
%* the eqn in text book is for r in nm
%A = 1.436;
B = 5.86e-6;
En = @(r) B/r^9 - A/r
%% find En,min at r = r0 us fminbnd command
[r0, Emin] = fminbnd(En, 0, 1);
disp('InterAtomic spacing for Min E, r0 in nm =')
disp (r0)
%% Calc En,min = En(r0)
En_min = En(r0);
disp('Min E, En_min in eV =')
disp (En_min)%
% Set Plotting Vector as 300 points
r_plt = linspace (0.1, .4, 300); % in nm
%% The Energy Functions
EA = -A./r_plt;
ER = B./r_plt.^8;
Etot = EA + ER;
%% Plot on Same Graph
plot(r_plt,EA, r_plt,ER, r_plt, Etot), xlabel('r (InterAtom
Spacing)'),...
ylabel('Energy'), title('ENGR45 Problem 2.14'), grid,...
legend('EA', 'ER', 'Etot'), axis([.1 .4 -8 8])
%% Compare to eqn 2.11 solution
n = 9;
disp('by eqn 2.11')
r0eqn = (A/(n*B))^(1/(1-n))
E0eqn = -A/(A/(n*B))^(1/(1-n)) + B/(A/(n*B))^(n/(1-n))
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Bruce Mayer, PE Engineering-45: Materials of Engineering
NaCl electron ExchangeNaCl electron Exchange
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Bruce Mayer, PE Engineering-45: Materials of Engineering
WhiteBoard Work – P2.13WhiteBoard Work – P2.13
Ca2+ & O2-