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CHAPTER 2:

CHAPTER 2:. Atomic Structure and Interatomic Bonding. ISSUES TO ADDRESS . • What promotes bonding?. • What types of bonds are there?. • What properties are inferred from bonding?. BOHR ATOM. Nucleus: Z = # protons. = 1 for hydrogen to 94 for plutonium. N = # neutrons.

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CHAPTER 2:

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  1. CHAPTER 2: Atomic Structure and Interatomic Bonding Dr. Mohammad Abuhaiba

  2. ISSUES TO ADDRESS... • What promotes bonding? • What types of bonds are there? • What properties are inferred from bonding? Dr. Mohammad Abuhaiba

  3. BOHR ATOM Nucleus: Z = # protons = 1 for hydrogen to 94 for plutonium N = # neutrons Atomic mass A ≈ Z + N Dr. Mohammad Abuhaiba

  4. ELECTRON ENERGY STATES Electrons... • have discrete energy states • tend to occupy lowest available energy state. Dr. Mohammad Abuhaiba

  5. STABLE ELECTRON CONFIGURATIONS Stable electron configurations... • have complete s and p subshells • tend to be unreactive. Dr. Mohammad Abuhaiba

  6. SURVEY OF ELEMENTS • Most elements: Electron configuration not stable. Dr. Mohammad Abuhaiba

  7. THE PERIODIC TABLE • Columns: Similar Valence Structure Electropositive elements: Readily give up electrons to become + ions. Electronegative elements: Readily acquire electrons to become - ions. Dr. Mohammad Abuhaiba

  8. ELECTRONEGATIVITY • Ranges from 0.7 to 4.0, • Large values: tendency to acquire electrons. Smaller electronegativity Dr. Mohammad Abuhaiba Larger electronegativity

  9. IONIC BONDING • Occurs between + and - ions. • Requires electron transfer. • Large difference in electronegativity required. • Example: NaCl Dr. Mohammad Abuhaiba

  10. EXAMPLES: IONIC BONDING Give up electrons Acquire electrons Dr. Mohammad Abuhaiba

  11. COVALENT BONDING • Requires shared electrons • Example: CH4 C: has 4 valence e, needs 4 more H: has 1 valence e, needs 1 more Electronegativities are comparable. Dr. Mohammad Abuhaiba

  12. EXAMPLES: COVALENT BONDING • Molecules with nonmetals • Molecules with metals and nonmetals Dr. Mohammad Abuhaiba • Elemental solids (RHS of Periodic Table) • Compound solids (about column IVA)

  13. METALLIC BONDING • Arises from a sea of donated valence electrons (1, 2, or 3 from each atom). • Primary bond for metals and their alloys Dr. Mohammad Abuhaiba

  14. SUMMARY: BONDING Type Bond Energy Comments Ionic Large! Nondirectional (ceramics) Variable Directional Covalent large-Diamond semiconductors, ceramics small-Bismuth polymer chains) Variable Metallic large-Tungsten Nondirectional (metals) small-Mercury Dr. Mohammad Abuhaiba

  15. PROPERTIES FROM BONDING: TM • Melting Temperature, Tm • Bond length, r • Bond energy, Eo Tm is larger if Eo is larger. Dr. Mohammad Abuhaiba

  16. PROPERTIES FROM BONDING: E • Elastic modulus, E • E ~ curvature at ro E is larger if Eo is larger. Dr. Mohammad Abuhaiba

  17. PROPERTIES FROM BONDING: a • Coefficient of thermal expansion, a • a ~ symmetry at ro a is larger if Eo is smaller. Dr. Mohammad Abuhaiba

  18. SUMMARY: PRIMARY BONDS Ceramics Large bond energy large Tm large E small a (Ionic & covalent bonding): Variable bond energy moderate Tm moderate E moderate a Metals (Metallic bonding): Polymers Directional Properties Secondary bonding dominates small T small E large a (Covalent & Secondary): Dr. Mohammad Abuhaiba

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