Chem #3 Exam

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Karina
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178284
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Chem #3 Exam
Updated:
2012-10-18 21:23:08
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chemistry chem
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flashcards for 3rd chemistry test
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  1. What is the description of Ionic Bonds?
    a chemical bond formed by the electrostatic attraction between positive and negative ions
  2. Formation of Ionic Bonds
    Involves the transfer of one or more electrons from the valence shell of one atom to the valence shell of another
  3. When are Ionic Bonds most likely to occur?
    Especially prevalent in compounds formed between Group 1A and 2A elements with Group 6A and 7A elements
  4. What is Lattice Energy?
    the energy required to completely separate one mole of a solid ionic compound inot gaseous ions
  5. How can you determine Lattice Energies?
    • They can be calculated from Coulomb's law or measured indirectly by the Born-Haber cycle
    • **cannot be measured directly**
  6. Coulombs Law (equation)
  7. Born-Haber Cycle
    Allows the indirected determination of the lattice energy of an ionic solid
  8. What is a Covalent Bond?
    a chemical bond formed by the sharing of a pair of electrons between atoms
  9. What are the multiple bonds?
    • Single Bond: a single pair of electrons is shared by two atoms
    • Double Bond: two pairs of electrons are shared by two atoms (often C, N, O and S)
    • Triple Bond: three pairs of electrons are shared by two atoms (often C and N)
  10. What is Bond Length?
    The distance between the nuclei of two covalent atoms in a molecule
  11. What are Intramolecular Forces?
    the attractive forces that holds the atoms together within a molecule
  12. What are Intermolecular Forces?
    • the forces that operate between molecules
    • *relatively weak in covalent compounds
    • **very strong in ionic compounds
  13. What is a Polar Covalent Bond?
    a covalent bond in which the bonding electrons spend more time near one atom that the other
  14. What are the Three types of Polar covalent bonds?
    • Pure covalent bond: neutral atoms held together by equally shared electrons
    • Polar covalent bond: partially charged atoms held toegher by unequally shared electrons
    • Pure ionic bond: oppositely charged ions held together by electrostatic attraction
  15. What is electronegativity?
    a measure of the ability of an atom in a molecule to draw bonding electrons to itself
  16. Robert S. Mulliken
    • came up with the Mulliken scale which calculates average ionization potential and electron affinity.
    • (no longer use the Mulliken scale)
  17. Linus C. Pauling
    • Created the Pauling Scale - derived from bond energies and is very widely used.
    • X increases left to right, decreases top to bottom
  18. What are the Five most electronegative elements?
    • F : 4.0
    • O : 3.5
    • N~Cl : 3.0
    • Br : 2.8
  19. Electron Affinity vs. Electronegativity
    • Electron Affinity: how much an isolated atom wants someone else's electrons
    • Electronegativity: how much an atom wants the shared electrons in a chemical bond
  20. Bond Polarity
    Polarity of a bond depends upon the difference in electronegativity of the two bonded atoms
  21. Bond Polarity and Bonding:
    -if Delta X is < than 0.5...?
    -if 0.5 is < Delta X and < 2.0...?
    -if Delta X is greater than or equal to 2.0...?
    • -if Delta X is < 0.5 the bond is purely covalent (nonpolar)
    • -if 0.5 is < Delta X and < 2.0 the bond is polar covalent
    • -if Delta X is greater than or equal to 2.0 the bond is ionic
  22. What is a Formal Charge?
    the hypothetical charge of an atom
  23. What are Resonance Structures?
    all possible Lewis Structures for a single molecule that cannot be represented accurately by only one Lewis structure
  24. What is delocalized bonding?
    a type of bonding in which a pair of bonding electrons is spread over a number of atoms rather than localized between two
  25. What are the exceptions to the octet rule?
    • -molecules having an odd number of electrons
    • -molecules with an atom from Group IIA or IIIA having < 8 valence electrons around that atom
    • -molecules with an atom having unfilled nd orbitals may have > 8 valence electrons around that atom
  26. What are bond enthalpy?
    the enthalpy charge Delta H required to break a particular bond in one mole of gaseous molecules
  27. What is average bond enthalpy?
    the average enthalpy change for the breaking of an A-B bond in the gas phase
  28. What is Bond Order?
    • the number of pairs of electrons in a bond
    • Trends:
    • -Bond enthalpy- increases with bond order
    • -Bond length- decreases with bond order
  29. What is Molecular Geometry?
    the three-dimensional arrangements of atoms in a molecule

    *Importance: a molecule's geometry affects its physical and chemical properties
  30. Valence-Shell Electron-Pair Repulsion (VSEPR) Model
    -Predicts the shape of molecules and ions

    Basis: Valence-shell electron-pairs (bonding and nonbonding) are kept as far away from one another as possible
  31. What are Electron Domains?
    - a lone pair of electrons or a chemical bond

    **Note: Double and Triple bonds are treated like Single bonds and count as one electron domain
  32. VSEPR Model Definitions:
    Arrangement of electron domains
    Molecular geometry
    • Arrangement of electron domains: determined by total number of electron domains (i.e., # of bonds AND non-bonding pairs)
    • Molecular geometry: determined by number of bonds

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