ENGR-45_Lec-02_AtomicBonding.ppt 1 Bruce Mayer, PE Engineering-45: Materials of Engineering Bruce Mayer, PE Registered Electrical & Mechanical Engineer Engineering 45 Atomic Structure and InterAtomic Bonding

ENGR-45_Lec-02_AtomicBonding.ppt 2 Bruce Mayer, PE Engineering-45: Materials of Engineering Learning Goals  Understand the Sources/Causes of Atom-Level Bonding  Understand The Number & Types of Bonding  Determine Which properties May be inferred from bonding trends

ENGR-45_Lec-02_AtomicBonding.ppt 3 Bruce Mayer, PE Engineering-45: Materials of Engineering The 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

ENGR-45_Lec-02_AtomicBonding.ppt 4 Bruce Mayer, PE Engineering-45: Materials of Engineering Atomic 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 = 1.6x Ampsec Note: 1 As = 1 Coulomb (C)

ENGR-45_Lec-02_AtomicBonding.ppt 5 Bruce Mayer, PE Engineering-45: Materials of Engineering Atomic Facts cont  Since The No. of NEUTRONS Are not Constrained by Charge Neutrality, 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

ENGR-45_Lec-02_AtomicBonding.ppt 6 Bruce Mayer, PE Engineering-45: Materials of Engineering Recall the Periodic Table

ENGR-45_Lec-02_AtomicBonding.ppt 7 Bruce Mayer, PE Engineering-45: Materials of Engineering Atomic Facts cont.2  Atomic Weight/Mass, A  Weighted Average of Naturally Occurring Isotopes  SubAtomic Particle Masses Electron, e - = 9.11x kg Proton, p +, and Neutron, n = x kg  Since M p+ & M n >> M e- Then A  (Z+N)M n

ENGR-45_Lec-02_AtomicBonding.ppt 8 Bruce Mayer, PE Engineering-45: Materials of Engineering amu & gMol  By SI DEFINITION grams of 12 C contains ONE gram-Mol of Carbon 1 Mol of Any element Contains 6.023x10 23 Protons and/or Electrons –6.023x10 23  Avagrado’s Number  Atomic Mass Unit, amu 1 amu/atom = 1 g/mol –e.g.; Atomic Wt of Niobium = amu/atom = g/mol

ENGR-45_Lec-02_AtomicBonding.ppt 9 Bruce Mayer, PE Engineering-45: Materials of Engineering Atomic Reactions  Nuclear Reaction Change in the Number of Neutrons, N, or Protons, Z, in an Atom –Remember, Changing Z Changes the ELEMENT TYPE  e.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

ENGR-45_Lec-02_AtomicBonding.ppt 10 Bruce Mayer, PE Engineering-45: Materials of Engineering Electron 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

ENGR-45_Lec-02_AtomicBonding.ppt 11 Bruce Mayer, PE Engineering-45: Materials of Engineering Bohr Atom  1 st Quantum Model Electrons Revolve Around Nucleus at Discrete Energy Levels 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

ENGR-45_Lec-02_AtomicBonding.ppt 12 Bruce Mayer, PE Engineering-45: Materials of Engineering Atom: Shells & Valence Nucleus Proton Neutron INNER Shell Electron VALENCE Electron VALENCE Shell/Orbit

ENGR-45_Lec-02_AtomicBonding.ppt 13 Bruce Mayer, PE Engineering-45: Materials of Engineering Atom 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

ENGR-45_Lec-02_AtomicBonding.ppt 14 Bruce Mayer, PE Engineering-45: Materials of Engineering Valence e - 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

ENGR-45_Lec-02_AtomicBonding.ppt 15 Bruce Mayer, PE Engineering-45: Materials of Engineering Electron Configuration of Atoms  Four QUANTUM NUMBERS Describe the Electronic Configuration of Atoms 1 st Shell 2 nd Sub-shell 3 rd # Electrons Per Sub-shell 4 th Spin  n d p s s s p M L K 3rd Quantum No. Describes the Number of VALENCE Electrons

ENGR-45_Lec-02_AtomicBonding.ppt 16 Bruce Mayer, PE Engineering-45: Materials of Engineering Electron Energy States  e - have DISCRETE energy states; tend to occupy LOWEST available energy state. 1s1s 2s2s 2p2p K-shell n = 1 L-shell n = 2 3s3s 3p3p M-shell n = 3 3d3d 4s4s 4p4p 4d4d Energy N-shell n = 4

ENGR-45_Lec-02_AtomicBonding.ppt 17 Bruce Mayer, PE Engineering-45: Materials of Engineering Shell Filling Rules  Following Quantum Mechanics 1.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)

ENGR-45_Lec-02_AtomicBonding.ppt 18 Bruce Mayer, PE Engineering-45: Materials of Engineering Electronic Configuration Principal Quantum No. SubShell Electrons Per 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

ENGR-45_Lec-02_AtomicBonding.ppt 19 Bruce Mayer, PE Engineering-45: Materials of Engineering Stable Electron Configurations  Stable Electron Configurations Have COMPLETE s & p SubShells –i.e., The VALENCE SubShell is FULL Are VERY Unreactive “OCTET” RULE: Ns 2 Np 6

ENGR-45_Lec-02_AtomicBonding.ppt 20 Bruce Mayer, PE Engineering-45: Materials of Engineering Periodic Table Structure n=1 (1s 1 ) n=2 (2s 1 ) n=3 (3s 1 ) n=4 (4s 1 ) Rows (valence shells) Columns (valence electron structure)

ENGR-45_Lec-02_AtomicBonding.ppt 21 Bruce Mayer, PE Engineering-45: Materials of Engineering 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) METALS NONMETALS Radii More ElectroNegLess ElectroNeg

ENGR-45_Lec-02_AtomicBonding.ppt 22 Bruce Mayer, PE Engineering-45: Materials of Engineering Periodic Table Structure  Organized by Quantum No., Valence (or Group), and SubShell

ENGR-45_Lec-02_AtomicBonding.ppt 23 Bruce Mayer, PE Engineering-45: Materials of Engineering Metals, SemiMetals, NonMetals s p d f Quantum No.

ENGR-45_Lec-02_AtomicBonding.ppt 24 Bruce Mayer, PE Engineering-45: Materials of Engineering Metals, 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

ENGR-45_Lec-02_AtomicBonding.ppt 25 Bruce Mayer, PE Engineering-45: Materials of Engineering Refined Shell Model for Nitrogen Valence SHELL (L or 2) Valence SUBShell (2p)

ENGR-45_Lec-02_AtomicBonding.ppt 26 Bruce Mayer, PE Engineering-45: Materials of Engineering Molecular 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

ENGR-45_Lec-02_AtomicBonding.ppt 27 Bruce Mayer, PE Engineering-45: Materials of Engineering Bond-Energy Curve  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”: r 0 - equilibrium bond distance Force Energy Min U

ENGR-45_Lec-02_AtomicBonding.ppt 28 Bruce Mayer, PE Engineering-45: Materials of Engineering Ionic 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 1s 2 2s 2 2p 6 3s 1 Na (cation) Stable 1s 2 2s 2 2p 6 Cl (nonmetal) Unstable 1s 2 2s 2 2p 6 3s 2 3p 5 electron Coulombic Attraction Cl (anion) Stable 1s 2 2s 2 2p 6 3s 2 3p X

ENGR-45_Lec-02_AtomicBonding.ppt 29 Bruce Mayer, PE Engineering-45: Materials of Engineering Ionic Bonding Examples  Dominant Bonding Type for CERAMICS Give up electronsAcquire electrons

ENGR-45_Lec-02_AtomicBonding.ppt 30 Bruce Mayer, PE Engineering-45: Materials of Engineering CoValent Bonding  Requires SHARED Electrons (Co-Valent)  Example is CH 4 (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 Cl 2

ENGR-45_Lec-02_AtomicBonding.ppt 31 Bruce Mayer, PE Engineering-45: Materials of Engineering CoValent Bonding Examples  NonMetallic Elemental Molecules; e.g. F 2  Hydrogen Compounds; e.g., HF, HNO 3  Elemental Solids; e.g., C, Si, Ge  Near Group-IVA Solid Compounds; e.g. GaAs

ENGR-45_Lec-02_AtomicBonding.ppt 32 Bruce Mayer, PE Engineering-45: Materials of Engineering Mixed Ionic+Covalent Bonding  Many Compounds Exhibit Ionic-Covalent Mixed Bonding where X A & X B are Pauling ElectroNegativities  Example MgO: X Mg = 1.3, X O = 3.5

ENGR-45_Lec-02_AtomicBonding.ppt 33 Bruce Mayer, PE Engineering-45: Materials of Engineering Metallic 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

ENGR-45_Lec-02_AtomicBonding.ppt 34 Bruce Mayer, PE Engineering-45: Materials of Engineering Secondary 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  Liquifying Force for Electrically Neutral and Symetrical Molecules such as H 2, N 2

ENGR-45_Lec-02_AtomicBonding.ppt 35 Bruce Mayer, PE Engineering-45: Materials of Engineering 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  e.g.; HCl Liquid  e.g.; Polymer Solid

ENGR-45_Lec-02_AtomicBonding.ppt 36 Bruce Mayer, PE Engineering-45: Materials of Engineering Secondary 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 = H 2 O to Form Liquid or Solid

ENGR-45_Lec-02_AtomicBonding.ppt 37 Bruce Mayer, PE Engineering-45: Materials of Engineering Summary: Chemical Bonding

ENGR-45_Lec-02_AtomicBonding.ppt 38 Bruce Mayer, PE Engineering-45: Materials of Engineering Properties From Bonding: T Melt  Bond Length  Melting Temperature, T M  Bond Energy, E 0  General Relationship: |E 0 |↑  T M ↑ r larger T M smaller T M Energy (r) r o r E o = “bond energy” Energy (r) r o r unstretched length

ENGR-45_Lec-02_AtomicBonding.ppt 39 Bruce Mayer, PE Engineering-45: Materials of Engineering Properties From Bonding: E  Modulus of Elasticity Defined  Modulus of Elasticity  Curvature of E vs r curve  Mathematically, E  General Relationship: |E 0 |↑  E ↑ r larger E Smaller E Energy r o unstretched length cross sectional area A o LL length,L o F undeformed deformed

ENGR-45_Lec-02_AtomicBonding.ppt 40 Bruce Mayer, PE Engineering-45: Materials of Engineering Properties From Bonding:   Coefficient of Thermal Expansion, , Defined   ~symmetry at r 0  Mathematically,   General Relationship: |E 0 |↑   ↑ r Larger  Smaller  Energy r o  L length,L o unheated, T 1 heated, T 2 =  (T 2 -T 1 )  L L o coeff. thermal expansion

ENGR-45_Lec-02_AtomicBonding.ppt 41 Bruce Mayer, PE Engineering-45: Materials of Engineering Summary: Primary Bonds Ceramics (Ionic & covalent bonding): Metals (Metallic bonding): Polymers (Covalent & Secondary): Large bond energy large T m large E small  Variable bond energy moderate T m moderate E moderate  Directional Properties Secondary bonding dominates small T m small E large 

ENGR-45_Lec-02_AtomicBonding.ppt 42 Bruce Mayer, PE Engineering-45: Materials of Engineering All Done for Today α Superimposed On Periodic Table  GALLUIUM is the Tall Yellow one  SODIUM is th Tall Blue one

ENGR-45_Lec-02_AtomicBonding.ppt 43 Bruce Mayer, PE Engineering-45: Materials of Engineering WhiteBoard Work – P2.13  K + & O 2- dipotassium oxide = K 2 O r 0 = 1.5 nm

ENGR-45_Lec-02_AtomicBonding.ppt 44 Bruce Mayer, PE Engineering-45: Materials of Engineering Problem Tutorial Let’s Work Text Problem 2.14  Calcuim Oxide →

ENGR-45_Lec-02_AtomicBonding.ppt 45 Bruce Mayer, PE Engineering-45: Materials of Engineering P2.13

ENGR-45_Lec-02_AtomicBonding.ppt 46 Bruce Mayer, PE Engineering-45: Materials of Engineering P2.13

ENGR-45_Lec-02_AtomicBonding.ppt 47 Bruce Mayer, PE Engineering-45: Materials of Engineering P2.13

ENGR-45_Lec-02_AtomicBonding.ppt 48 Bruce Mayer, PE Engineering-45: Materials of Engineering P2.14

ENGR-45_Lec-02_AtomicBonding.ppt 49 Bruce Mayer, PE Engineering-45: Materials of Engineering P2.14

ENGR-45_Lec-02_AtomicBonding.ppt 50 Bruce Mayer, PE Engineering-45: Materials of Engineering 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 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([ ]) % % 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))

ENGR-45_Lec-02_AtomicBonding.ppt 51 Bruce Mayer, PE Engineering-45: Materials of Engineering NaCl electron Exchange

ENGR-45_Lec-02_AtomicBonding.ppt 52 Bruce Mayer, PE Engineering-45: Materials of Engineering WhiteBoard Work – P2.13  Ca 2+ & O 2-