CHEM 101 Exam 2
Material coverage: Ch. 2.5-2.6; Ch. 3 (3.1-3.7); Ch. 4 (4.1-4.3; 4.6) - selections as taught in lectures and
indicated in the Course Schedule
For problem-solving practice on the "Review Topics" listed below, you may use (this order is recommended):
- recitation "Answer Keys";
- problems solved in class (see "Lecture Notes");
- practice questions in the "Practice Questions" folder and "Review Session" questions & answers;
- problems solved in the short videos posted in the "Videos for Better Understanding" folder;
- textbook solved problems within the chapter;
- textbook "Conceptual connections" within the chapter (detailed answers at the end of the chapter);
- textbook "Self-assessment quizzes" at the end of each chapter (answers on the same page) - only questions related
to the topics below;
- "Modified Mastering Chemistry" problems
Note: Mastering Chemistry questions are meant to help you actively learn the material taught in lectures by
problem-solving, so the level of difficulty for these questions varies from very easy to very difficult. Therefore, not all
Mastering Chemistry questions are candidates for exam questions.)
Review Topics: You may receive exam questions from any of the topics listed below.
NOTE: You will be tested on scientific notation, units of measure conversion, and particles-moles-mass
conversions on each exam, since those are concepts with general applications in science.
1. The Quantum-Mechanical Model of the Atom: 2.5-2.6
- hypothesis: electrons can also behave as waves, so wave equations can be used to calculate their 3D-trajectories;
- atomic orbitals:
- definition;
- notations;
- main energy shell (level) vs. subshell (sublevel) within a main energy level vs. orbital within a subshell;
- know how to count:
- subshells per shell;
- orbitals per subshell;
- orbitals per shell;
2. The Periodic Table and Electron Configuration: 3.1-3.3
- know how to read the periodic table;
- know the chemical information provided by groups vs. periods related to the general structure of atoms and ions;
- know how to recognize "families of elements" (main group elements vs. transition metals vs. metalloids);
Electron Configuration (as predicted using the quantum-mechanical model):
- definition;
- Pauli exclusion principle; define paired and unpaired electrons;
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- define degenerate orbitals = orbitals of equal energy that constitute an energy subshell (sublevel);
- know how to write electron configurations using spdf notations and orbital diagrams (filling subshells in
order of increasing energy (aufbau principle); Hund’s rule; Pauli exclusion principle);
- know how to calculate the number of electrons in completely filled shells and/or subshells.
3. Shielding vs. penetration effects. Core vs. valence electrons: 3.3-3.5
- define effective nuclear charge, Zeff;
- explain the shielding (screening) effect and its role in changing the effective nuclear charge;
Note: If you still struggle with understanding the effective nuclear charge and the shielding effect, please
watch the video posted on the course website in the “Videos for Better Understanding” folder /
“Shielding and the Nuclear Effective Charge" subfolder.
- explain how penetration (orbital overlap) can affect Zeff and an electron's potential energy;
- define core and valence electrons; know how to count them in given electron configurations;
- know how to determine the number of valence electrons from the number of the group for main groups elements;
- know why valence electrons are the most important in chemical bonding;
- know how to use the electron configuration of the valence shell to explain:
- why atoms gain, lose, or share electrons (hint: think of the "energy cost" per electron removed or added);
- why elements of the same group have similar properties;
- the classification of elements as block of elements and families of elements.
- the positive and negative charge for cations and anions, respectively;
(hint: consider the number of protons vs. the number of electrons)
- know how to predict the charge for monoatomic ions from main groups using the number of the group;
- know how to write electron configurations for atoms and ions using the noble gas (shorthand) notation;
4. Periodic Trends: 3.6-3.7
- define each periodic property:
- atomic radius;
- ionic radius;
- ionization energy;
- based on electron configuration, explain the screening (shielding) effect within a group and across a period;
explain how this effect determines changes in periodic properties along groups and rows of the periodic table;
- know how to rank elements based on atomic/ionic radii and on ionization energies (use the electron configuration
of the valence shell to rank elements based on first and second ionization energy, respectively);
know how to explain the ranking based on the effective nuclear charge determined by shielding;
pay attention to the exceptions to the first ionization energy trends discussed in the textbook (and in class).
Note: If you still struggle with understanding and solving problems with periodic trends correlated with the electron
configuration or if you just need more practice, please watch the short videos posted on the course website in the
“Videos for Better Understanding” folder / “Periodic Trends” subfolder.
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5. Chemical bonding: 4.1-4.3; 4.6
- covalent vs. ionic;
- molecular compounds (exist as molecules) vs. ionic compounds (exist as lattices of ions);
Note: All compounds are neutral, whether molecular or ionic!
- know the type of chemical formulas and how to interpret them:
- molecular formula (shows the ratio between atoms in a molecule - see the Law of Definite Proportions) vs.
formula unit (shows the ratio between ions of opposite charges in an ionic lattice);
- based on chemical formulas, know how to calculate:
- number of each type of atoms per molecule;
- number of each type of ions per formula unit;
- number of atoms or ions per mole of a given substance;
- from the "Conductivity" experiment:
- know what conductivity is and what it measures;
- classification of substances as electrolytes and non-electrolytes based on ionic dissociation;
- classification of electrolytes as weak or strong;
- know how to explain "conductivity-ionic charge-number of ions" dependence.
~ We wish you success! ~
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