Re-Cap of General Chemistry I

Hey everyone!

Before we recap General Chemistry I, let’s talk about the homework for our upcoming Verbal I session next time.

Your required homework for the Verbal Reasoning I session:

• VR Review Notes (Verbal Reasoning Section):  Chapters 1-3
• VR Review Notes (Writing Sample Section):  Chapters 1-5

For those of you who would like some additional Verbal Reasoning practice before class, I recommend the following:

• Verbal Reasoning Foundation Review Unit 1
• OWQ:  Critical Reading Skills
• Completing these assignments will be a good warm-up for the Verbal I session, in which we will more formally introduce how to approach this section of the exam.  Most of the class will be devoted to discussing the Verbal Reasoning portion of the test, but we’ll spend about thirty to forty-five minutes on the Writing Sample section as well.

To reinforce what we have covered in General Chemistry I, complete the following:

• General Chemistry Subject Tests 1 & 2

• Electronic Structure and Periodic Table Test 1
• The second passage picks up on a conversation we had earlier in class regarding how electrons load (Aufbau principle) and come off a free atom.  Neither passage set is as difficult as the question sets typically encountered in the Physics topical tests.
• Both of these passages have a number of pseudodiscrete questions.  This points out why it’s so important to critically read!  If you absorb all the details, you may spend a ton of time learning information you’ll never need.
• Bonding Test 1
• The first question of the first passage may seem mind-blowing but think critically when you go to answer it; then it won’t take too long at all!

All of these items are available on your syllabus through www.kaptest.com.

Helpful hints:

• Don’t forget to use your High-Yield Problem Solving Guide for additional practice – these questions are at the back of each book and take a “cook book” approach to the 100 most commonly tested problems in the MCAT sciences, including step-by-step analysis of sample problems, key concepts, takeaways, and similar questions for you to try on your own (the answers for the “Similar Problems” are also in the back).
• Remember that the Periodic Table tab is located at the bottom of the computer screen.  Clicking on the tab will pull up the Periodic Table in its entirety, covering the passage and the question.  Familiarize yourself with the periodic trends for quick reference to the table on Test Day.  You don’t have to have the periodic table memorized, but you should definitely be familiar with where the elements are so that you aren’t spending a solid minute just searching for zinc.
• Be sure to know and understand ideal gas behaviors, as quantified by the equations, and what factors cause real gases to deviate from predicted (ideal) behavior.  Learn the names of the different ideal gas laws as the MCAT may refer to the law by name (e.g. Boyle’s Law; Charles’s Law).

General Chemistry I Concept Review:

• Atomic Structure:  Know each quantum number and names of important rules (e.g. Hund’s Rule, the Aufbau Principle).
• Periodic Table & Periodic Trends
• Know how to use periodic table to determine atomic number (Z), atomic mass (A), valence electron shell configuration, and some chemical properties for any given element.  Also, know the name for some of the important groups (alkali metals, alkaline earth metals, noble gases, halogens, chalcogens).
• Know all the periodic trends; they’re easy to derive if framed from perspective of Z_eff (pull of nucleus on valence shell) – or, as I like to think of it, how much elements “love on” their electrons.
• Remember that half-filled stability creates exceptions in trends for ionization energy (IE) and electron affinity (EA).
• Be able to distinguish between EA and electronegativity (there are no exceptions to the electronegativity trend from half-filled orbitals).
• Bonding (intramolecular interactions within a molecule)
• Be able to predict when ionic bonds or covalent bonds would predominate; know the definition of polar and coordinate covalent bonds
• Know how to draw Lewis structure for any given compound (keep the Octet Rule and formal charges in mind).
• Molecular Geometry:  memorize the table, and understand the difference between “electronic” and “molecular” geometry.
• Intermolecular Forces (attractive forces between different molecules)
• Know the relative strengths of the four intermolecular forces and how they are used to predict boiling point and melting point trends
• Although London/van der Waals/Dispersion forces are the weakest, they can be quite significant for very large molecules; trivia:  this is how geckos can climb shear surfaces.
• Hydrophobic interactions are sometimes classified as an intermolecular force, but we’ll review that in Organic Chemistry III when we talk about peptides.
• Gases
• Know the properties of an ideal gas (random motion, no volume, elastic collisions, average kinetic energy being proportional to temperature).
• Know Boyle’s Law versus Charles’s Law versus Avogadro’s Principle as well as the famous Ideal Gas Law equation (PV = nRT)
• Know that the volume occupied by an ideal gas is 22.4 L/mol at STP (STP is 0°C/273 K and 1 atmosphere of pressure).
• Know Dalton’s Law and how to use it to determine the partial pressure of one gas within a mixture of gases (see the Critical Thinking Exercise on page 74 of the Lesson Book).
• Be familiar with Graham’s Law by name even though it’s merely a re-arrangement of the fact that average kinetic energy is proportional to temperature.
• van der Waals Equation of State (Real Gases)
• Real pressures (what we observe) are usually lower than expected due to attractive intermolecular forces.  This factor will become significant at moderately high pressures (or moderately low volumes).
• Real volume (what we observe, i.e. volume of container) is greater than the actual free volume of space available to the gas molecules because the gas molecules actually occupy space.  This factor only becomes significant at extremely high pressures (or extremely small volumes).
• These trends are reflected in the attached image (each distinct curve is what we observe for one mole of gas).  Note that at moderately high pressures (up to 200-400 atm), the volume is smaller than predicted; at very high pressures (above 400), the volume is larger.
• If we have one mole of an ideal gas, then PV/RT should equal 1.  And I know H₂ doesn’t quite fit, but I don’t have a great explanation for that.
• Take away points:
• At moderately high pressure/low volume/low temperature, we’ll have a smaller volume than predicted (that is, real volume < ideal volume) because of attractive intermolecular forces.
• At extremely high pressure/low volume/low temperature, we’ll have a larger volume than predicted (that is, real volume > ideal volume) because the gas molecules actually occupy space.

Well, that’s all the MCAT stuff I’ve got for now.  See you soon!