![Chapter 2 - 2
Atomic Structure (Freshman Chem.)
• atom – electrons – 9.11 x 10-31
kg
protons
neutrons
• nucleus of atom: “size of a point on a page” -! فراغ
• atomic number = No. of protons in nucleus of atom
= No. of electrons of neutral species
A [=] atomic mass unit = amu = 1/12 mass of 12
C
Atomic wt = wt of 6.023 x 1023
molecules or atoms
Unit 1 amu/atom = 1g/mol
C 12.011
H 1.008 etc.
} 1.67 x 10-27
kg](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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Properties depend on bonding interactions
- 1. Chapter 2 - 1 Properties depend on - arrangement of atoms - interactions between atoms Study Bonding: • What promotes bonding? • What types of bonds are there? • What properties are inferred from bonding? CHAPTER 2: BONDING AND PROPERTIES
- 2. Chapter 2 - 2 Atomic Structure (Freshman Chem.) • atom – electrons – 9.11 x 10-31 kg protons neutrons • nucleus of atom: “size of a point on a page” -! فراغ • atomic number = No. of protons in nucleus of atom = No. of electrons of neutral species A [=] atomic mass unit = amu = 1/12 mass of 12 C Atomic wt = wt of 6.023 x 1023 molecules or atoms Unit 1 amu/atom = 1g/mol C 12.011 H 1.008 etc. } 1.67 x 10-27 kg
- 3. Chapter 2 - 3 Atomic Structure • Valence electrons: in the outer-shell • determine all of the following properties 1) Chemical: reactivity 2) Electrical: conductivity 3) Thermal: conductivity 4) Optical: transmittance
- 4. Chapter 2 - 4 Electronic Structure - Review • Electrons have wavelike and particulate properties. – This means that electrons are in orbitals defined by a probability. – Each orbital at discrete energy level determined by quantum numbers. Quantum # Designation n = principal (energy level-shell) K, L, M, N, O (1, 2, 3, etc.) l = subsidiary (orbitals) s, p, d, f (0, 1, 2, 3,…, n-1) ml = magnetic (direction in space) 1, 3, 5, 7 (-l to +l) ms = spin ½, -½
- 5. Chapter 2 - 5 Electron Energy States 1s 2s 2p K-shell n = 1 L-shell n = 2 3s 3p M-shell n = 3 3d 4s 4p 4d Energy N-shell n = 4 • have discrete energy states • tend to occupy lowest available energy state. Electrons...
- 6. Chapter 2 - 6 • Why? Valence (outer) shell usually not filled completely. • Most elements: Electron configuration not stable. SURVEY OF ELEMENTS - Review Electron configuration (stable) ... ... 1s22s22p 63s23p 6 (stable) ... 1s22s22p 63s23p 63d 10 4s24p6 (stable) Atomic # 18 ... 36 Element 1s11Hydrogen 1s22Helium 1s22s13Lithium 1s22s24Beryllium 1s22s22p 15Boron 1s22s22p 26Carbon ... 1s22s22p 6 (stable)10Neon 1s22s22p 63s111Sodium 1s22s22p 63s212Magnesium 1s22s22p 63s23p 113Aluminum ... Argon ... Krypton
- 7. Chapter 2 - 7 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 • Primary Bonding: Ionic, Covalent and Metallic • example: C (atomic number = 6) 1s2 2s2 2p2 valence electrons
- 8. Chapter 2 - 8 Electronic Configurations ex: Fe - atomic # = 26 valence electrons 1s 2s 2p K-shell n = 1 L-shell n = 2 3s 3p M-shell n = 3 3d 4s 4p 4d Energy N-shell n = 4 1s2 2s2 2p6 3s2 3p6 3d6 4s2
- 9. Chapter 2 - 9 The Periodic Table • Columns: Similar Valence Structure Electropositive elements: Readily give up electrons to become + ions. Electronegative elements: Readily acquire electrons to become - ions. giveup1e giveup2e giveup3e inertgases accept1e accept2e O Se Te Po At I Br He Ne Ar Kr Xe Rn F ClS Li Be H Na Mg BaCs RaFr CaK Sc SrRb Y
- 10. Chapter 2 - 10 • Ranges from 0.7 to 4.0, Smaller electronegativity Larger electronegativity • Large values: tendency to acquire electrons. Electronegativity
- 11. Chapter 2 - 11 Ionic bond – metal + nonmetal donates accepts electrons electrons Dissimilar electronegativities ex: MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4 [Ne] 3s2 Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6 [Ne] [Ne] 1s22s22p 6 (stable)10Neon
- 12. Chapter 2 - 12 • Occurs between + and - ions. • Requires electron transfer. • Large difference in electronegativity required. • Example: NaCl Ionic Bonding Na (metal) unstable Cl (nonmetal) unstable electron + - Coulombic Attraction Na (cation) stable Cl (anion) stable
- 13. Chapter 2 - 13 • Predominant bonding in Ceramics Examples: Ionic Bonding Give up electrons Acquire electrons NaCl MgO CaF2 CsCl
- 14. Chapter 2 - 14 C: has 4 valence e - , needs 4 more H: has 1 valence e - , needs 1 more Electronegativities are comparable. Covalent Bonding • similar electronegativity ∴ share electrons • bonds determined by valence – s & p orbitals dominate bonding • Example: CH4 shared electrons from carbon atom shared electrons from hydrogen atoms H H H H C CH4
- 15. Chapter 2 - 15 Primary Bonding • Metallic Bond -- delocalized as electron cloud • Ionic-Covalent Mixed Bonding % ionic character = where XA & XB are Pauling electronegativities %)100(x1−e − (XA−XB)2 4 ionic70.2%(100%)xe1characterionic% 4 )3.15.3( 2 = −= − − Ex: MgO XMg = 1.3 XO = 3.5
- 16. Chapter 2 - 16 Arises from interaction between dipoles • Permanent dipoles-molecule induced • Fluctuating dipoles -general case: -ex: liquid HCl -ex: polymer Adapted from Fig. 2.14, Callister 7e. SECONDARY BONDING asymmetric electron clouds + - + - secondary bonding HH HH H2 H2 secondary bonding ex: liquid H2 H Cl H Cl secondary bonding secondary bonding + - + - secondary bonding secondary bonding
- 17. Chapter 2 - 17 Type Ionic Covalent Metallic Secondary Bond Energy Large! Variable large-Diamond small-Bismuth Variable large-Tungsten small-Mercury smallest Comments Nondirectional (ceramics) Directional (semiconductors, ceramics polymer chains) Nondirectional (metals) Directional inter-chain (polymer) inter-molecular Summary: Bonding
- 18. Chapter 2 - 18 Interactions Between Atoms + - + - r + - + - Spacing (r) Atomic Radius (R) Far Atoms: Attraction Close Atoms: Repulsion Equilibrium spacing = ro ro = 2 R + - + - Dynamic Equilibrium
- 19. Chapter 2 - 19
- 20. Chapter 2 - 20 Bonding Curve
- 21. Chapter 2 - 21 Bonding Curve • Energy – minimum energy most stable – Energy balance of attractive and repulsive terms Attractive energy EA Net energy EN Repulsive energy ER Interatomic separation r r A n r B EN = EA + ER = −−ro
- 22. Chapter 2 - 22 Bonding - Estimations • Estimation of Bonding Energy (Eo) and Equilibrium Spacing (ro) • Given: • Bonding occurs at energy minimum • At minimum: Derivative dE/dr = g(r) = 0 • Solve g(r) = 0 for r ro • Substitute r=ro in the Energy Eqn: • Get Eo = E (r=ro) • Atomic radius R = ro/2 Eo = “bond energy” Energy ro r r A n r B E = certain f(r) e.g. E = − For many atoms, ro is approximately 0.3 nm.
- 23. Chapter 2 - 23 • Bond length, r • Bond energy, Eo • Melting Temperature, Tm Tm is larger if Eo is larger. Properties From Bonding: Tm ro r Energy r larger Tm smaller Tm Eo = “bond energy” Energy ro r unstretched length
- 24. Chapter 2 - 24 • Coefficient of thermal expansion, α • α ~ symmetry at ro α is larger if Eo is smaller. Properties From Bonding : α = α (T2-T1) ∆L Lo Coefficient of thermal expansion ∆L length, Lo unheated, T1 heated, T2 ro r Smaller α Larger α Energy unstretched length Eo Eo
- 25. Chapter 2 - 25 Ceramics (Ionic & covalent bonding): Metals (Metallic bonding): Polymers (Covalent & Secondary): Large bond energy large Tm large E small α Variable bond energy moderate Tm moderate E moderate α Directional Properties Secondary bonding dominates small Tm small E large α Summary: Primary Bonds secondary bonding Bonding in Solids > Liquids > Gases
- 26. Chapter 2 - 26 Reading: Focus on Atomic Bonding in Solids Core Problems: 2.7, 2.8, 2.12, 2.13, 2.17, 2.19, 2.21 (Callister 3rd Addition) Quiz: Next Class ANNOUNCEMENTS
- 27. Chapter 2 - 27 Quiz Energy Atomic Spacing rA B c Rank materials A, B and C according to 1. Increasing melting temperature > > 2. Decreasing bonding energy > > 3. Increasing Atomic Radius > > 4. Increasing coefficient of thermal expansion > >
- 28. Chapter 2 - 28 Quiz Energy Atomic Spacing r A B c Rank materials A, B and C according to 1. Increasing melting temperature > > 2. Decreasing bonding energy > > 3. Increasing Atomic Radius > > 4. Increasing coefficient of thermal expansion > >