2017 Spring Semester Quiz 1
For General Chemistry I (CH101)
Date: Mar 20 (Mon),
Professor Name
Time: 19:00 ~ 19:45
Class
Student I.D. Number
Name
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Use the following constants to solve problems.
(Planck constant 𝒉𝒉 = 6.626 × 10-34 J s)
(Mass of electron 𝒎𝒎𝒆𝒆 = 9.109 × 10-31 kg)
-12 2 -1
-1
(Charge of the electron 𝒆𝒆 = 1.602 × 10-19 C)
(Permittivity of the vacuum 𝜺𝜺𝟎𝟎 = 8.854 × 10 C J m )
23
-1
(Avogadro’s number 𝑵𝑵𝑨𝑨 = 6.022 × 10 mol ) (Ratio of a circle's circumference to its diameter 𝝅𝝅 = 3.142)
R
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1. (Total 10 pts, each 2 pts) Read the following statements or equations, and verify whether these
are “TRUE (T)” or “FALSE (F)”. (2 pts for a right answer, -2 pts for a wrong answer, 0 pt for no answer)
(a) Based on Rutherford’s planetary model of the atom, the total energy of the electron in the
hydrogen atom is
Answer: ______F_______
𝐄𝐄 =
𝒁𝒁𝒆𝒆𝟐𝟐
𝟏𝟏
𝒎𝒎𝒆𝒆 𝒗𝒗𝟐𝟐 +
𝟒𝟒𝟒𝟒𝜺𝜺𝟎𝟎 𝒓𝒓
𝟐𝟐
(b) The second ionization energy, 𝑰𝑰𝑰𝑰𝟐𝟐 , is the minimum energy required to remove a second
electron, as represented by the process
Answer: ______T_______
𝑿𝑿+ (𝒈𝒈) → 𝑿𝑿𝟐𝟐+ (𝒈𝒈) + 𝒆𝒆−
∆𝐄𝐄 = 𝑰𝑰𝑰𝑰𝟐𝟐
(c) If the octet rule is not satisfied to write Lewis diagram, elements in the second period are
allowed to share more than 8 electrons.
Answer: ______F_______
(d) Microwave, another type of electromagnetic radiation travels with the speed c, as same with
light.
Answer: ______T_______
(e) The value of a wave function 𝝍𝝍, which maps out the amplitude of a wave in three dimensions,
can be positive, zero, or negative.
Answer: ______T_______
2. (Total 8 pts) In ionic compounds, the potential energy (𝐕𝐕(𝑹𝑹𝟏𝟏𝟏𝟏 )) is expressed as a function of
the distance between the ions (𝑹𝑹𝟏𝟏𝟏𝟏 ), choosing as zero the potential energy of the neutral atoms
when they are infinitely far apart.
𝐕𝐕(𝑹𝑹𝟏𝟏𝟏𝟏 ) = 𝑨𝑨𝒆𝒆−𝜶𝜶𝑹𝑹𝟏𝟏𝟏𝟏 − 𝑩𝑩 �
(𝒆𝒆)(−𝒆𝒆)
𝑹𝑹𝟏𝟏𝟏𝟏
� + ∆𝑬𝑬∞ ,
where the first term represents the repulsion between ions as they get close together, the
second term is the attractive Coulomb potential, and the third term is the energy required to
create the ions from their respective neutral atoms.
(a) (3 pts, no partial points) Consider the ionic compound 𝑲𝑲𝑲𝑲. Given that the first ionization energy
of potassium is 419 kJ/mol and electron affinity of fluorine is 328 kJ/mol, calculate ∆𝑬𝑬∞ .
∆𝑬𝑬∞ = 𝑰𝑰𝑬𝑬𝟏𝟏 (𝑲𝑲) − 𝑬𝑬𝑬𝑬(𝑭𝑭) = +𝟗𝟗𝟗𝟗 𝒌𝒌𝒌𝒌/𝒎𝒎𝒎𝒎𝒎𝒎
b) (5 pts) Estimate the energy of dissociation (∆𝑬𝑬𝒅𝒅 ) to neutral atoms for 𝑲𝑲𝑲𝑲 , which has a bond
length 2.17 x 10-10 m.
U
---
∆𝑬𝑬𝒅𝒅 식쓰면
+2 pt
--- 답 +3 pts
3. (Total 6 pts, each 2 pts) Based on VSEPR theory, draw Lewis diagrams with the smallest formal
charges, and name the geometry for given molecules. If there are possible resonance forms,
please draw all of them.
(a) 𝑪𝑪𝑪𝑪𝑪𝑪𝟒𝟒 P
O
O
O
Cl
O
O
O
Cl
O
O
O
O
O
Cl
O
O
O
Cl
O
O
All 4 resonance structures should be drawn ----------------------------------------------------------- + 1 pt
Geometry: Tetrahedral
-------------------------------------------------------------------------------------- + 1 pt
(b) 𝑩𝑩𝑩𝑩𝑩𝑩𝑩𝑩𝟐𝟐
Be
Cl
Cl
Geometry: Linear
---------------------------------------------------------------------------------------------- + 1 pt
--------------------------------------------------------------------------------------------- + 1 pt
(c) 𝑷𝑷𝑷𝑷𝟓𝟓
F
F
F
P
F
F
---------------------------------------------------------------------------------------------------- + 1 pt
Geometry: Trigonal bipyramidal
----------------------------------------------------------------------------- + 1 pt
4. (8 pts) The Bohr theory started from Rutherford’s planetary model of the atom. By Rutherford’s
model, the total energy of the electron in the Hydrogen atom is
𝐄𝐄 =
𝒁𝒁𝒆𝒆𝟐𝟐
𝟏𝟏
𝒎𝒎𝒆𝒆 𝒗𝒗𝟐𝟐 −
𝟒𝟒𝟒𝟒𝜺𝜺𝟎𝟎 𝒓𝒓
𝟐𝟐
From this equation, derive the allowed energy values of the energy 𝑬𝑬𝒏𝒏 in terms of 𝒁𝒁, 𝒆𝒆, 𝒎𝒎𝒆𝒆 , 𝜺𝜺𝟎𝟎 ,
𝒏𝒏, and 𝒉𝒉 based on the Bohr theory.
(Hint: Bohr postulated that the angular momentum is quantized in integral multiples of
𝒉𝒉
𝟐𝟐𝟐𝟐
)
답만 맞으면 3점. 부분 점수는 위 그림에 맞게 배점하고, 그 외 풀이 과정에 대해서는 없습니다.
5. (Total 8 pts) Consider the following two systems, and calculate the energy difference between
ground state and first excited state for each system. Express your answer in kJ/mol.
(a) (4 pts) an electron in a one-dimensional box of length 1.0 Å
- E ground , E first 둘다
맞게 구하면 + 1 pt
- ∆𝑬𝑬 식 쓰면 + 1 pt
--- 답 맞으면 + 2 pts.
(b) (4 pts) a helium atom in cube 30 cm on an edge. (Mass of a helium atom is 6.64 x 10-27 kg.)
--- E ground , E first 둘다
맞게 구하면 + 1 pt
- ∆𝑬𝑬 식 쓰면 + 1 pt
-- 답 맞으면 + 2 pts.