Humboldt State University ® Department of Chemistry

Richard A. Paselk

SA 560B; 826-5719

Final Exam Study Guide

Spring 2015 version

The Final Exam will be Comprehensive!

Approximately 1/3–1/2 will focus on recent material and those things you need to know to understand latest material, while the remainder will be on materials from previous Exam 1 Study Guide, Exam 2 Study Guide, and Exam 3 Study Guide.

The Final will consist of multiple choice questions as well as a few problems (about 1/3) with partial credit focused on the material covered since the last exam - check out the on-line sample to see the types and distribution of question types etc.

Review

Homework since Exam III (see suggested problems on Schedule). Review Quizzes (see Keys on my Moodle site), particularly those on materials since exam III. Review nomenclature so that you can read questions and understand them. Review concepts from exams I, II, & III that we have used in looking at additional systems etc.

Be able to convert numbers to scientific notation and use numbers expressed in scientific notation; do all calculations with proper significant figures; make all conversions within the metric system (SI).

Covalent Bonding – A Quantum View (Chapter 9)

When atomic orbital sets are filled, or half-filled they become completely symmetrical. Orbitals are orbitals: 1) Only two electrons can be accommodated in any orbital. 2) No two electrons can have the same "address" (the same set of quantum numbers). 3) For a molecule the "address" becomes the molecule over which the electrons are shared rather than the atom. 4) We have conservation of orbitals - a molecule will have the same number of orbitals as the atoms which make up the molecule. 5) For our purposes we can also assume a conservation of orbital energy.

Hybrid Atomic Orbitals

What are hybrid atomic orbitals? What do we mean when we say this is a "localized electron" model? What does it tell us about the electron distribution in molecules? Why are hybrid orbitals popular? (relatively easy to calculate/visualize). What are their limitations? (NOT looking at molecules, so can only be a limited approximation.) How are bonds visualized with hybrid orbitals? Know the five common hybrid orbital sets (sp, sp2, sp3, dsp3, d2sp3) and their geometries (linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral). Be able to describe the molecular geometries we discussed with VSEPR Theory in terms of hybrid orbitals. Does the hybrid orbital set correspond to the electronic or to the molecular geometry?

What are the two basic bond types in molecular orbitals? (Sigma (sigma) bonds - cylindrically symmetrical around the axis connecting the bonded atoms, and Pi (pi) bonds - made up of two lobes with planar symmetry around a plane though the nuclei of the two bonded atoms.) Note that single bonds are always sigma bonds, and in a multiply bonded system the "central" bond is a sigma bond. The "second" and "third" bond of multiply bonded atoms are pi bonds. For systems with two pi bonds the bond panes are perpendicular to each other and the two bonds form a symmetrical cylinder around the sigma bond. What is resonance and why is it needed in hybrid orbital theory? How is this a "failure" of the theory? Why does hybrid orbital theory not give information about electronic energy levels in molecules?

Be able to describe the hybridization of atoms in molecules given their structures, and be able to specify the bond types (sigma or pi) between atoms in a structure. (Sample question: Give the hybridization for each atom and the bond types for: CH3CCCH2COH.) See Also Hybrid Molecular Orbital Module

Molecular Orbital Model of Bonding

How does MO theory differ from hybrid orbital theory? What advantages does it have over hybrid orbital theory? Disadvantages? Be able to draw energy diagrams. Know and be able to explain the molecular energy diagrams we discussed in lecture. How is bonding described in MO theory? Are bond shapes the same (sigma & pi)? Be able to determine when molecules are diamagnetic or paramagnetic and explain why. Be able to give the bond order of a diatomic molecule. Define bond order. (Sample questions: 1) Draw a Molecular Orbital Energy-level diagram for NO (lecture 34). Include all of the valence electrons in your diagram, and determine the bond order and whether the molecule should be diamagnetic or paramagnetic based on your diagram. 2) Draw a molecular orbital energy-level diagram for NO showing the original atomic energy levels and the MO energy-levels. )

Liquids & Solids (Chapter 10)

Define/describe: weak forces, Hydrogen bonds, vapor pressure, phase change, boiling, solid,. Why is water's boiling point so high (vapor pressure so low)? How does it compare to other molecules? Are there any molecules with similarly high boiling points? Why do liquids boil? When? Why are boiling points lower in the mountains? Explain cooling by evaporation. Molar heats of vaporization and condensation. What is supercooling? superheating? Why do they occur? What is bumping? a seed crystal? Explain sublimation, triple point, critical point. Equilibrium vapor pressure.

What is a solid? crystal? glass? How do we know about the detailed structures of solids? Be able to solve simple problems using the Bragg eqn. What is a lattice? a unit cell? Know the three cubic unit cells. How many "atoms" are there in each? Be able to solve simple density and volume problems involving unit cells (e.g. an element which forms crystals with a simple cubic unit cell has an atomic radius of x.xx, what is its density?). What is close packing?

What kinds of bonds and forces hold solids together? What are van der Waal's forces? London dispersion forces? Hydrogen bonds? Dipole-dipole bonds? Be familiar with the various types of solids (molecular, ionic, covalent metallic), their characteristic properties, and how these correlate with the bonds/forces holding them together. Sublimation.

Energy of Formation: How is it calculated? What is lattice energy? How is it calculated? (Sodium chloride example, lecture 30) Heat of crystallization. Bond Energies and Enthalpies of Reaction - Be able to calculate enthalpies of reaction given bond energies (lecture 31).

Solutions (Chapter 11)

Define/describe: solution, salt, solvent, solute, saturated solution, unsaturated solution, super saturated solution, mass %, ppm, ppb, molarity (M), molality (m), mole fraction (X), neutralization, equivalent (in chemical reactions). Why do some substances dissolve in each other? Why do others not? ("Like Dissolves Like").

How does solubility vary with temperature? Why? How does the solubility of gases vary with pressure? Explain this variation. What is Henry's law? Raoult's law? Ideal solution. What does each relate to? How are they different? What are colligative properties? What do they depend on?

You may bring one-half sheet of 8.5 x 11 paper (8.5"x5.5") with any information you like on both sides (93.5 square inches) as a "cheat sheet" for the final.

You should be careful and thorough in designing and creating this sheet.

Remember it is for reference and insurance, the less you rely on it the better off you will be!

Note also that you will be provided with the Periodic Table and the equations and constants sheet posted on Moodle.


 

Syllabus / Schedule

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© R A Paselk

Last modified 29 April 2015