lOMoARcPSD|4832048 Lec.2 Atomic Structure & Bonding Material science (Qassim University) StuDocu is not sponsored or endorsed by any college or university Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Chapter 2: Atomic Structure & Interatomic Bonding ISSUES TO ADDRESS... • What promotes bonding? • What types of bonds are there? • What properties are inferred from bonding? Chapter 2 - 1 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Solar System Via Atomic Structure Chapter 2 - 2 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Atomic Structure (Freshman Chem.) • atom – electrons – 9.11 x 10-31 kg protons 1.67 x 10-27 kg neutrons } • atomic number = # of protons in nucleus of atom = # of electrons of neutral species • A [=] atomic mass unit = amu = 1/12 mass of 12C Atomic wt = wt of 6.022 x 1023 molecules or atoms 1 amu/atom = 1g/mol C H 12.011 1.008 etc. Chapter 2 - 3 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Atomic Structure • Valence electrons determine all of the following properties 1) 2) 3) 4) Chemical Electrical Thermal Optical Chapter 2 - 4 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Electronic Structure • Electrons have wavelike and particulate properties. – This means that electrons are in orbitals defined by a probability. – Each orbital at discrete energy level is determined by quantum numbers. Quantum # Designation n = principal (energy level-shell) l = subsidiary (orbitals) ml = magnetic K, L, M, N, O (1, 2, 3, etc.) s, p, d, f (0, 1, 2, 3,…, n -1) 1, 3, 5, 7 (-l to +l) ms = spin ½, -½ Chapter 2 - 5 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Electron Energy States Electrons... • have discrete energy states • tend to occupy lowest available energy state. 4d 4p N-shell n = 4 3d 4s Energy 3p 3s M-shell n = 3 Adapted from Fig. 2.4, Callister & Rethwisch 8e. 2p 2s L-shell n = 2 1s K-shell n = 1 Chapter 2 - 6 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 SURVEY OF ELEMENTS • Most elements: Electron configuration not stable. Element Hydrogen Helium Lithium Beryllium Boron Carbon ... Atomic # 1 2 3 4 5 6 Electron configuration 1s 1 1s 2 (stable) 1s 2 2s 1 1s 2 2s 2 1s 2 2s 2 2p 1 1s 2 2s 2 2p 2 ... Adapted from Table 2.2, Callister & Rethwisch 8e. Neon Sodium Magnesium Aluminum ... 10 11 12 13 1s 2 2s 2 2p 6 (stable) 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 3s 2 1s 2 2s 2 2p 6 3s 2 3p 1 ... Argon ... Krypton 18 ... 36 1s 2 2s 2 2p 6 3s 2 3p 6 (stable) ... 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable) • Why? Valence (outer) shell usually not filled completely. Chapter 2 - 7 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Electron Configurations • Valence electrons – those in unfilled shells • Filled shells more stable • Valence electrons are most available for bonding and tend to control the chemical properties – example: C (atomic number = 6) 1s2 2s2 2p2 valence electrons Chapter 2 - 8 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Electronic Configurations ex: Fe - atomic # = 26 1s2 2s2 2p6 3s2 3p6 3d 6 4s2 4d 4p N-shell n = 4 valence electrons 3d 4s Energy 3p 3s M-shell n = 3 Adapted from Fig. 2.4, Callister & Rethwisch 8e. 2p 2s L-shell n = 2 1s K-shell n = 1 Chapter 2 - 9 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 give up 1egive up 2egive up 3e- • Columns: Similar Valence Structure accept 2eaccept 1einert gases The Periodic Table H He Li Be O F Ne Na Mg S Cl Ar Adapted from Fig. 2.6, Se Br Kr Callister & Rethwisch 8e. K Ca Sc Rb Sr Te Y I Xe Po At Rn Cs Ba Fr Ra Electropositive elements: Readily give up electrons to become + ions. Electronegative elements: Readily acquire electrons to become - ions. Chapter 2 - 10 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Electronegativity • Ranges from 0.7 to 4.0, • Large values: tendency to acquire electrons. Smaller electronegativity Larger electronegativity Adapted from Fig. 2.7, Callister & Rethwisch 8e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell University. Chapter 2 - 11 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Atomic bonding: an attempt to fill electron shells 1. 2. 3. 4. Ionic bonds Covalent bonds Metallic bonds Secondary Bonds (Van Der Walls) Chapter 2 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 IONIC BOND •Bond formed between two ions by the transfer of electrons •Between atoms of metals and nonmetals with very different electronegativity •Produce charged ions at all states. •Conductors and have high melting point. •Examples; NaCl, CaCl2, K2O Chapter 2 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Chapter 2 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Ionic bond – metal + donates electrons nonmetal accepts electrons Dissimilar electronegativities ex: MgO Mg 1s2 2s2 2p6 3s2 [Ne] 3s2 Mg2+ 1s2 2s2 2p6 [Ne] O 1s2 2s2 2p4 O2- 1s2 2s2 2p6 [Ne] Chapter 2 - 15 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 • • • • Ionic Bonding Occurs between + and - ions. Requires electron transfer. Large difference in electronegativity required. Example: NaCl Na (metal) unstable Cl (nonmetal) unstable electron Na (cation) stable + Coulombic Attraction Cl (anion) stable Chapter 2 - 16 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Ionic Bonding • Energy – minimum energy most stable – Energy balance of attractive and repulsive terms EN = EA + ER = - A r + B rn Repulsive energy ER Interatomic separation r Net energy EN Adapted from Fig. 2.8(b), Callister & Rethwisch 8e. Attractive energy EA Chapter 2 - 17 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Examples: Ionic Bonding • Predominant bonding in Ceramics NaCl MgO CaF 2 CsCl Give up electrons Acquire electrons Adapted from Fig. 2.7, Callister & Rethwisch 8e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell University. Chapter 2 - 18 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Covalent Bond •Between nonmetallic elements of similar electronegativity. •Formed by sharing electron pairs •Stable non-ionizing particles, they are not conductors at any state •Examples; O2, CO2, C2H6, H2O, SiC Chapter 2 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Chapter 2 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Covalent Bonding • similar electronegativity share electrons • bonds determined by valence – s & p orbitals dominate bonding • Example: CH4 C: has 4 valence e-, needs 4 more H: has 1 valence e-, needs 1 more Electronegativities are comparable. H CH 4 H C H shared electrons from carbon atom H shared electrons from hydrogen atoms Adapted from Fig. 2.10, Callister & Rethwisch 8e. Chapter 2 - 21 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Metallic Bond •Bond found in metals; holds metal atoms together very strongly •Formed between atoms of metallic elements •Electron cloud around atoms •Good conductors at all states, lustrous, very high melting points •Examples; Na, Fe, Al, Au, Co Chapter 2 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 A Sea of Electrons Chapter 2 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Primary Bonding • Metallic Bond -- delocalized as electron cloud • Ionic-Covalent Mixed Bonding % ionic character = (X A -X B )2 4 1e x (100%) where XA & XB are Pauling electronegativities Ex: MgO XMg = 1.2 XO = 3.5 ( 3.5-1.2 )2 4 % ionic character 1 - e x (100%) 73.4% ionic Chapter 2 - 24 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 SECONDARY BONDING Arises from interaction between dipoles • Fluctuating dipoles asymmetric electron clouds + - secondary bonding + - ex: liquid H 2 H2 H2 H H H H secondary bonding Adapted from Fig. 2.13, Callister & Rethwisch 8e. • Permanent dipoles-molecule induced -general case: + - secondary bonding + Adapted from Fig. 2.15, Callister & Rethwisch 8e. -ex: liquid HCl -ex: polymer H Cl secondary bonding H Cl secondary bonding Chapter 2 - 25 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Summary: Bonding Comments Type Bond Energy Ionic Large! Nondirectional (ceramics) Covalent Variable large-Diamond small-Bismuth Directional (semiconductors, ceramics polymer chains) Metallic Variable large-Tungsten small-Mercury Nondirectional (metals) Secondary smallest Directional inter-chain (polymer) inter-molecular Chapter 2 - 26 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Properties From Bonding: Tm • Bond length, r • Melting Temperature, Tm Energy r • Bond energy, Eo ro Energy r smaller Tm unstretched length ro larger Tm r Eo = “bond energy” Tm is larger if Eo is larger. Chapter 2 - 27 Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Properties From Bonding : a • Coefficient of thermal expansion, a length, L o coeff. thermal expansion unheated, T1 DL DL Lo heated, T 2 = a(T2 -T1) • a ~ symmetric at ro Energy unstretched length ro E o E r a is larger if Eo is smaller. larger a smaller a Chapter 2 - 28 o Downloaded by Batata Basal (t.osaily23@gmail.com) lOMoARcPSD|4832048 Summary: Primary Bonds Ceramics Large bond energy (Ionic & covalent bonding): Metals large Tm large E small a Variable bond energy moderate Tm moderate E moderate a (Metallic bonding): Polymers Directional Properties (Covalent & Secondary): Secondary bonding dominates small Tm small E large a Chapter 2 - 29 Downloaded by Batata Basal (t.osaily23@gmail.com)