Name ________________________

AP Chemistry By Satellite

John I. Gelder

Exam III

November 12, 1991

** INSTRUCTIONS**:

1. This examination consists of a total of 11 different pages. The last three pages include a periodic table and some useful information, a table of standard bond energies and an activity series. All work should be done in this booklet.

2. PRINT your name, high school, teaching partner's name and the date now in the space at the top of this sheet. DO NOT SEPARATE THESE PAGES.

3. Answer all questions that you can and whenever called for show your work clearly. Your method of solving problems should pattern the approach used in lecture. You do not have to show your work for the multiple choice or short answer questions.

4. No credit will be awarded if your work is not shown in problems 7 or 8.

5. Point values are shown next to the problem number.

6. Budget your time for each of the questions. Some problems may have a low point value yet be very challenging. If you do not recognize the solution to a question quickly, skip it, and return to the question after completing the easier problems.

7. Look through the exam before beginning; plan your work; then begin.

8. Relax and do well.

APCBS Exam III KEY PAGE 2

(9) 1. Write the chemical formula(s) of the product(s) and balance any **three** of the following five reactions.
Identify all products phases as either (g)as, (l)iquid, (s)olid or (aq)ueous.

(14)2a. Consider the energy levels of a hypothetical atom,

(2)b. Draw an arrow on your diagram showing the transition of an electron from E_{4} to E_{1}.

(2)c. Is energy absorbed or emitted when this transition occurs?

** Energy is emitted in this transition.**

(3)d. Calculate the energy of the photon of light absorbed or emitted.

(4)e. Calculate the frequency of the photon of light absorbed or emitted.

** (1 point for units, 1 point for math, 2 points for the correct equation)**

APCBS Exam III KEY PAGE 3

(12) 3. Answer Option 1 and any **one** of the remaining three options on this page.

Option 1: Which has the smaller atomic radius, Cl or Si? Explain your answer in terms of *effective nuclear
charge* and *shielding effects*.

** Cl has a smaller atomic radius compared to Si. Both elements have their outer
electrons in the 3p orbitals. Si has a nuclear charge of +14 and Cl has a nuclear
charge of +17. Since the electrons in the 3p orbitals do not shield each other
fromn the charge on the nucleus, the 3p electrons in Cl "feel" a greater effective
nuclear charge compared to the electrons in Si. The result is the 3p electrons in Cl
are pulled closer to the nucleus and the atomic radius is smaller compared to Si.**

** (2 points for Cl smaller than Si, 2 points for shielding and 2 points for effective
nuclear charge. In explaining effective nuclear charge 1 point for the fact that it is
higher for Cl compared to Si and 1 point for the connection that the higher e.n.c.
results in a greater attraction and a smaller radius.)**

Option 2: Briefly explain what the term *degeneracy* means when used to describe features of the energy level
diagram for a multi-electron atom.

** Degeneracy means equal in energy. In a multi-electron atom, orbitals in the same
subshell are degenerate. For example the three orbitals in the p subshell are all
degenerate in energy.**

** (3 points for degeneracy and 3 points for sublevel idea.)**

Option 3: Define *electronegativity* and state the overall trend observed going down a group and across a
period in the periodic table.

** Electronegativity is a measure of the attraction an atom has for the electrons it
shares in a chemical bond. The electronegativity decreases going down a group
and it increases going across a period.**

** (2 points for the correct definition, 2 points for the group trend, 2 points for the
period trend.)**

Option 4: Briefly describe the difference between an *orbit* and an *orbital* as it relates to an electron in a
hydrogen atom.

** An orbit is a circular path around the nucleus. According to Bohr's model, only
orbits with specific radii are allowed. Orbits are specified by a single quantum
number. An orbital is a volume of space specified by 3 quantum numbers where
the probability of finding the electron is greatest.**

** (3 points for the orbit explanation and 3 points for the orbital.)**

APCBS Exam III KEY PAGE 4

4. Short answer.

(5) a) Which of the following has the highest lattice energy

MgF_{2}, KF, NaF, AlF_{3}, RbF

Briefly, explain your choice.

(4) b) Write the possible set of quantum numbers for a valence electron in an antimony (Sb) atom in its ground state.

** [Kr] 5s**

(4) c) Given the five orbital diagrams labeled A, B, C, D, and E.

From the orbital diagrams select an example which demonstrates

i). a violation of Hund's rule** C**

ii). a violation of the Pauli exclusion principle** D**

iii). a ground state orbital diagram** A**

iv). an excited state orbital diagram** E or B**

v). a violation of the Aufbau principle** B or E**

APCBS Exam III KEY PAGE 5

(15) 5. Draw a Lewis electron-dot structure for each of the covalent molecules below. Include all resonance
structures if they are needed to adequately represent the bonding in the molecule.

(8) 6. Write the electron configuration for each of the following.

a) Se^{2-
}** [Ar] 4s**^{2}**3d**^{10}**4p**^{6}** or 1s**^{2}**2s**^{2}**2p**^{6}**3s**^{2}**3p**^{6}**4s**^{2}**3d**^{10}**4p**^{6}

b) Mn

** [Ar] 4s**^{2}**3d**^{5}** or 1s**^{2}**2s**^{2}**2p**^{6}**3s**^{2}**3p**^{6}**4s**^{2}**3d**^{5}

c) Ir

** [Xe] 6s**^{2}**4f**^{14}**5d**^{7}** or 1s**^{2}**2s**^{2}**2p**^{6}**3s**^{2}**3p**^{6}**4s**^{2}**3d**^{10}**4p**^{6}**5s**^{2}**4d**^{10}**5p**^{6}**6s**^{2}**4f**^{14}**5d**^{7}

APCBS Exam III KEY PAGE 6

(10) Solve **ONE** of the two problems on this page. (A second problem will not be scored.)

7. An APCBS student went into the laboratory to run **Experiment 5: Heat of Neutralization**. After
calibrating the thermistor, the student began to measure the heat capacity of the calorimeter. 50.0 mL of
56.3 ºC water was added to 50.0 mL of 24.0 ºC water in the calorimenter. The maximum temperature
of the mixture was 42.1 ºC. The density of water is 1.00 g/mL and the specific heat of water is 4.184
J/g ºC.

A) Calculate the heat capacity of the calorimeter.

B) Explain why the student should not be satisified with the value of the heat capacity of the calorimeter
obtained in Part A.

** The heat capacity is negative, so when heat is absorbed, it gets colder (lower
temperature). This is the opposite of what is expected, so the student has made an
error in the experiment.**

8. Using bond energies calculate DHº for the reaction

** (Deduct 2 points for a math error or if units are missing in the answer. Deduct 4
points for the first error in the number of bonds that are broken or formed or if the
wrong value of the bond energy is read from the table.)**

APCBS Exam III KEY PAGE 7

Multiple Choice:

Print the letter (A, B, C, D, E) which corresponds to the answer selected.

9.** A**
10.** D**
11.** A**
12.** C**
13.** A**

14.** D**
15.** D**
16.** B**
17.** E**

ONLY THE ANSWERS IN THE AREA ABOVE WILL BE GRADED. Select the most correct answer for each question. Each question is worth 2 points.

9. Which of the following elements has the largest ionization energy?

A) O

B) B

C) I

D) Cs

E) S

10. Which of the following is isoelectronic with Ba^{2+}?

A) Ca^{2+
} B) La^{2+
} C) O^{2-
} D) I^{-}

E) Rn

11. Which of the following has the smallest radius?

A) N

B) B

C) Al

D) Be

E) C

12. Which of the following groups contains compounds that do not obey the octet rule

A) NH_{3}, PH_{3}, SO_{3
} B) H_{2}O, CH_{2}Cl_{2}, CO_{2
} C) BF_{3}, SF_{4}, ICl_{3}^{-
} D) NO_{2}^{-}, SO_{3}^{2-}, SCN^{-}

E) HOCl, Cl_{2}CO, N_{2}H_{4}

APCBS Exam III KEY PAGE 8

13. A possible set of quantum numbers for the last electron added to complete the ground state electron
configuration for a neutral zinc atom is,

14. In which of the following substances is nitrogen in the most positive oxidation state?

A) NO

B) NO_{2
} C) NO_{2}^{-}

D) N_{2}O_{5
} E) NH_{4}^{+}

15. An atom of the element X has the electron configuration _____ 1*s*^{2}2s^{2}2p^{6}3s^{2}3p^{3
}

The compound most likely to form with Br is,

A) XBr

B) XBr_{2
} C) X_{2}Br_{3
} D) XBr_{3
} E) X_{3}Br_{2}

16. What is the electron configuration of a Co^{3+} ion?

A) [Ar]4d^{6
} B) [Ar]3d^{6
} C) [Ar]4s^{2}3d^{10
} D) [Ar]4s^{2}3d^{4
} E) [Ar]4s^{2}3d^{7}

17. Which of the following is isoelectronic with the nitrate ion?

A) NF_{3
} B) H_{3}O^{+
} C) SO_{3}^{2-
} D) NO_{2}^{-
} E) CO_{3}^{2-}