Week 2: Atomic Structure & Interatomic Bonding PDF

Chapter 2: Atomic Structure & Interatomic Bonding ISSUES TO ADDRESS... What characteristics of atoms/molecules promote interatomic/intermolecular bonding? What types of interatomic/intermolecular bonds exist ? What properties of mater...

Chapter 2: Atomic Structure & Interatomic Bonding ISSUES TO ADDRESS... What characteristics of atoms/molecules promote interatomic/intermolecular bonding? What types of interatomic/intermolecular bonds exist ? What properties of materials depend on the magnitude of interatomic/intermolecular bonds ? Chapter 2 - 1  Atomic Structure (Freshman Chem.) atom electrons – 9.11 x 10 -31 kg protons – neutron } 1.67 x 10-27 s atomic number kg = # of protons in nucleus of atom = # of electrons in neutral species atomic mass unit = amu = 1/12 mass of 12 C A = Atomic wt = wt of 6.022 x 1023 molecules or atoms 1 amu/atom = 1 g/mol C 12.011 H 1.008 Chapter 2 - 2 etc.  Atomic Structure (cont.) Some of the following properties are determined by an atom's electronic structure: 1) Chemical 2) Electrical 3) Thermal 4) Optical Chapter 2 - 3  Electronic Structure Electrons have wave-like and particle-like characteristics. Two wave-like characteristics are – Electron position in terms of probability density – shape, size, orientation of probability density determined by quantum numbers – Quantum # Designation/Values n = principal (shell) K, L, M, N, O (1, 2, 3, 4, ℓ = azimuthal (subshell) etc.) mℓ = magnetic (no. of s, p, d, f (0, 1, 2, 3 , … , n- orbitals) 1) ms = spin 1, 3, 5, 7(-ℓ to +ℓ) ½, -½ Chapter 2 - 4  Electron Energy Electrons... States have discrete energy values tend to occupy lowest available energy states 4 d N-shell n = 4 4 3 p d 4 M-shell n = Energ y s 3 32 p L-shell n = 3 2 2s s1 K-shell n = s 1 Chapter 2 - 5  SURVEY OF ELEMENTS Most elements: Electron configurations not stable. Element Atomic Electron Hydroge #1 configuration 1s1 n 2 1s2 (stabl Helium Lithium 3 1s2 2s1 e) Berylliu 4 1s2 2s2 m 5 1s2 2s2 2p Boron 6 1 Carbon... 1s2 2s2 2p 1 2 (stabl Neon Sodium 0... 1s2 2s2 2p 6 3s1 e) Magnesiu 1 1s2 2s2 2p 6 3s2 m 2 1 1s 6 2 2s2 2p 6 3s2 Aluminum 1 3p 1... 1 3... (stabl Argon 8 1s2 2s2 2p 6 3s2 e)... Krypton... 3p262s2 2p 6 3s2 3p 6 3d 10 4s2 4p 6 1s 36... (stable) Why not stable? Valence (outer) shell usually not completely filled. Chapter 2 - 6  Electron Configurations Valence electrons – those in outer unfilled shells Filled shells are more stable – require more energy to gain or lose electrons Valence electrons available for bonding and tend to determine an atom’s chemical properties 1s2 2s2 2p2 C (atomic number = 6) – example: valence electrons Chapter 2 - 7  Electronic Configurations (cont.) ex: Fe (atomic # = 26) Electron configuration 2s2 2p6 3s2 3d 6 1s2 3p6 4s2 4 N-shell n = valenc d 4 e 3 electron 4 dp s 4 3 M-shell n = Energ y sp 3 3 s2 L-shell n = p 2 2s 1 K-shell n = s 1 Chapter 2 - 8  The Periodic Elements in each column:Similar valence electron structure Table 1e- give up give up gases inert accept accept up 3e- 2e- 1e- 2e- H H Li Be O F e N M N give a g e K Ca Sc S Cl Ar Rb Sr Se Br Kr Y Cs Ba Te I Xe Fr Ra Po At Rn Electropositive Electronegative elements: Readily elements: Readily give up electrons to acquire electrons to Chapter 2 - become + ions. become - ions. 9  Electronegativity Ranges from 0.7 to 4.0, Large values: tendency to acquire electrons. Smaller Larger electronegativity electronegativity Chapter 2 - 10  Ionization Process metal atom + nonmetal atom donate accept s s electron electron Dissimilar s s electronegativities ex: MgO 1s2 2s2 2p6 O 1s2 2s2 Mg 3s2 [Ne] 2p4 3s22 Mg 1s 2s 2+ 2 O2- 1s2 2s2 2p6 2p6 [Ne] [Ne] Chapter 2 - 11  Ionic Occurs between + and - ions. Bonding Requires electron transfer. Large difference in electronegativity required. Example: NaCl Na Cl (metal) (nonmeta unstabl electro l) e n unstable Na + - Cl (cation Coulombi (anion) ) c stable stable Attractio n Chapter 2 - 12  Ionic Bonding Energy –(cont.) minimum energy most stable – Net energy = sum of attractive and repulsive energies – Equilibrium separation when net energy is a minimum EN = EA + ER = - rA + Repulsive energy rn ER B Interatomic separation r Net energy EN Fig. 2.10(b), Callister & Rethwisch 10e. Attractive energy EA Chapter 2 - 13  Ionic Bonding Predominant bonding in Example Ceramics (cont.) NaC s: l MgO CaF 2 CsCl Give up Acquire electrons electrons Chapter 2 - 14  Covalent Bonding  share electrons Similar electronegativities Bonds involve valence electrons – normally s and p orbitals are involved Example: H2 H2 Each H: has 1 valence e -, H H needs 1 more Electronegativiti es are the same. shared 1s shared 1s electron from electron from 1st hydrogen 2nd hydrogen atom atom Fig. 2.12, Calliser & Rethwisch 10e. Chapter 2 - 15 Covalent Bonding: Bond Hybrization Carbon can form sp 3 hybrid orbitals sp3 109.5 sp 3 ° C sp3 sp3 Fig. 2.14, Callister & Rethwisch 10e. (Adapted from J.E. Brady and F. Senese, Chemistry: Matter and Its Changes, 4th edition. Reprinted with permission of John Wiley and Sons, Inc.) Fig. 2.13, Callister & Rethwisch 10e. Chapter 2 - 16  Covalent Bonding (cont.) Hybrid sp3 bonding involving carbon Example: CH4 4 valence C: each has 1 sH electrons, needs 4 more sp3 H: each has 1 valence sp3 electron, needs 1 more sp3 H C 1 H s 1 H sp3 s Electronegativities of C 1 and H are similar so s Region of electrons are shared in sp3 overlap hybrid covalent bonds. Fig. 2.15, Callister & Rethwisch 10e. (Adapted from J.E. Brady and F. Senese, Chemistry: Matter and Its Changes, 4th edition. Reprinted with permission of John Wiley and Sons, Inc.) Chapter 2 - 17  Metallic Bonding Electrons delocalized to form an “electron cloud” Fig. 2.19b, Callister & Rethwisch 10e. Chapter 2 - 18  Mixed Bonding Most common mixed bonding type is Covalent-Ionic mixed bonding   ( XA XB )2  % ionic 1  e 4  x character =   (100%) where XA & XB are electronegativities of the two elements participating in the bond Ex: XMg = MgO 1.2 XO = 3.5   (3.51.2)2  % ionic character  4   x (100%)  1e 73.3% Chapter 2 - 19  Secondary Bonding Arises from attractive forces between dipoles Fluctuating dipoles asymmetric ex: liquid H electron H clouds 22 + - + H2 H secondar - y bonding H H H Permanent secondar dipoles y secondar -general + y + bonding case: - bondin - secondar g -ex: liquid H Cl y H Cl HCl bondin -ex: secon dary g bond ing linear polymer polymer molecule Chapter 2 - 20  Properties Related to Bonding I: Melting Bond Temperature (Tm) Temperature, Melting length, r Tm r Energy Bond energy, ro Eo r smaller Energy Tm unstretched length o larger m r r T Eo The larger Eo, the higher = “bond Tm energy” Chapter 2 - 21  Properties Related to Bonding II: Coefficient of Thermal Expansion Coefficient (l) of thermal expansion, length, l ΔL Lo unheated, = αl (T2 - ΔL Lo T1 T1) heated, T2 The smaller Eo, the larger αl. unstretched Increase in bond length is Energ length due to asymmetry of the E vs. r ro curve. This r results in an increase in l. y Eo larger αl As E0 increases this Eo asymmetry decreases. smaller αl Chapter 2 - 22  Summary: Properties Related to Bonding Type and Bonding EnergyLarge Ceramics bond (Ionic & covalent energy bonding): high Tm large Metals E (Metallic small bonding): αl Variable Polymers bond Weak bond energy (between (Covalent & energy chains) Secondary): moderate Secondary bonding secon dary bond Tm responsible for most ing moderate physical properties Elow Tm Chapter 2 - moderate small 23 αlE  SUMMARY A material’s chemical, electrical, thermal, and optical properties are determined by electronic configuration. Valence electrons occupy the outermost unfilled electron shell. Primary bonding types include covalent, ionic, and metallic bonding. Secondary or van der Waals bonds are weaker than the primary bonding types. The percent ionic character of a covalent-ionic mixed bond between two elements depends on their electronegativities. Chapter 2 - 24