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4 Ex exam 4    11/14

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Coverage for Exam 4: Exam 4 covers all the material that was covered on LE's 18-22 and HW07 and HW08. The exam is covers the last two sections of Chapter 4 (VB and MO Theories of Bonding) plus all of Chapter 5 (IMFs). There are four extra practice assignments (9 - 12) on canvas are a good way to prep for exam 4.

Length / Time for Exam 4: You should once again expect 20 multiple choice questions. The questions will have a range of point values from 4 points to 6 points although the default will be 5 points. Remember that the point values are included with all questions. The exam is given during class time (9:30-10:45, 11-12:15) which is 75 minutes total which includes the handout time.

Nomenclature continues to still be "active" You still need to know your polyatomic ions, formulas, charges, etc.

NO CALCULATORS on this Exam

Main Equations/Formulas for Exam 4

Coulomb's Law (force): \[F \propto {q_1q_2\over r^2} \]

Coulomb's Law (energy): \[E_{\rm p} \propto {q_1q_2\over r} \]

still useful for exam 3 is the mobile friendly set of

VSEPR Help Pages

For exam 4, the hybridization for those electronic geometries is especially important.

VSEPR Theory

Empirical. Shapes are predicted via "common sense" about electron regions repulsing each other.

VB Theory

The geometries needed for compounds are made by combining atomic orbitals into hybrid orbitals with the corresponding geometries. Sigma and pi bonding are introduced and are a key component of this bonding theory. All hybridizations are localized on the central atoms.

MO Theory

All of the atomic orbitals for the entire set of atoms in the molecule are used to create a new set of molecular orbitals. MO theory is much more "wholistic" meaning it includes all the nuclei and electrons to make molecular orbitals. The sigma and pi bonding concept is still in place, but antibonding orbitals are introduced as well.

Intermolecular Forces (IMFs)

Intermolecular forces are the forces that are between molecules. They are the forces that hold liquids and solids together - collectively known as cohesive forces.

dipole-dipole

All polar molecules have dipole-dipole forces of attraction. All the partial positive and negative charges pull the molecules together.

H bonding

A special case version of dipole-dipole that is much stronger than "plain" dipole-dipole. A partially positive H must be covalently bonded to a nitrogen, oxygen, or fluorine atom in order to have H-bonding.

dispersion forces

All molecules have dispersion forces. For non-polar molecules, dispersion forces are the only IMFs present. Dispersion forces are the weakest of the three forces when compared one to one in small molecules. However, dispersion forces scale with molecular size (surface area actually). So all large molecules (and atoms) tend to have large dispersion forces - so much so that all very large molecules are solids.

Learning Outcomes for Bonding

Students will be able too...

  1. Identify metals and non-metals, and predict the types of compounds (ionic/covalent) that will form from different elements.
  2. Distinguish between molecules, ions, and atoms.
  3. Predict the anion or cation that a main-group element is likely to form.
  4. Relate Coulomb’s law to ionic radii, ionic charge, and lattice energy.
  5. Describe the distance dependence of the potential energy of a covalent bond.
  6. Predict and explain relative bond strength and lengths in a compound.
  7. Name and write formulas for covalent compounds.
  8. Interpret line drawings of chemical compounds with implicit hydrogens, carbons, and lone pairs.
  9. Rank the polarity of covalent bonds based on relative electronegativity.
  10. Rank the polarity of covalent bonds based on relative electronegativity.
  11. Define dipole moment and identify polar bonds.
  12. Draw the best Lewis structure (including any resonance structures) for a molecule or polyatomic ion.
  13. Apply formal charges to structures and use them to predict the most likely structure.
  14. Recognize and apply exceptions to the octet rule.
  15. Apply the VSEPR model to determine a molecule's electronic and molecular geometry based on its Lewis dot structure.
  16. Assess if a molecule is polar based on polar bonds and its molecular geometry.
  17. ★ Identify the orbital hybridization for any atom in a given molecule using the VB model.
  18. ★ Describe the type of bond (e.g. sigma, pi) and the atomic orbitals that are associated with the bond using the VB model.
  19. ★ Differentiate between localized and delocalized electrons within a structure.
  20. ★ Diagram orbital hybridization using orbital notation.
  21. ★ Recognize that Molecular Orbital (MO) theory is used to determine the energy of the electron in a molecule as well as its geometry.
  22. ★ Differentiate between constructive interference and destructive interference of atomic orbitals.
  23. ★ Construct and fully interpret a MO diagram, including identifying the bond order, the lowest energy electronic excitation energy (HOMO-LUMO gap), and the magnetism (paramagnetic or diamagnetic) for a compound.

Note that many of the outcomes for exam 3 are also included here for exam 4. The strike outs will not specifically be tested on exam 4. The starred items (★) are the main new material for exam 4. However, much of the exam 3 material is needed to have a full understanding of the 16-22 ★ outcomes.

Learning Outcomes for IMFs

Students will be able to…..

  1. Define the three major intermolecular forces (IMFs) that can exist in condensed phases: dipole-dipole, hydrogen bonding, and dispersion.
  2. Predict the types of IMFs that a compound can exhibit based on its structure.
  3. Using bonding theories and IMFs, predict the chemical and physical properties of organic materials.
  4. Explain how size, shape and polarizability affect the magnitude of dispersion forces.
  5. Relate the IMFs of a compound to liquid properties such as boiling point, vapor pressure, viscosity, and surface tension.
  6. Explain how liquid properties vary with temperature.
  7. Fully describe (atomic arrangement/microscopic view) and visually depict the four types of solids (covalent, ionic, metallic, molecular).
  8. Summarize how the macroscopic properties of solids (e.g. melting point, hardness, conductivity) can be explained by the microscopic model of solids.
  9. Use physical data to deduce the type of bonding within solids.