Download 2008 midtermkey - University of Victoria

NAME _______________________________________ Student No. ___________________________
SECTION (circle one): A01 (Codding)
A02 (Lee/McIndoe) A03 (Briggs) A04 (Boyer)
UNIVERSITY OF VICTORIA
Version
A
CHEMISTRY 101
Mid-Term Test 1, October 17
2008
Version
A
This test has two parts:
PART I is a multiple choice section and is worth 30 marks. The answers for the 16 questions in this
part must be coded on the optical sense form using a SOFT PENCIL.
PART II consists of written answers and is worth 20 marks. Answer these questions on this
examination paper. Answers written partially or completely in pencil cannot be remarked.
Hand in this entire test paper as well as your optical sense form (bubble sheet) at the
end of the examination period (60 minutes). The basic Sharp EL510 calculator is the
only one approved for use in Chemistry 101.
Marks for Written Answers
Question 1 [5]
Question 2 [4]
Question 3 [3]
Question 4 [2]
Question 5 [1]
Question 6 [2]
Question 7 [3]
TOTAL (/20)
Multiple Choice (/30)
Raw Score (/50)
TOTAL MARK (%)
Chemistry 101, Mid-Term Test 1
Version A
Page 2 of 8
PART I – Multiple Choice: Select the BEST response for each question below. [Total marks = 30]
1. This is exam Version A. Mark “A” as the answer to question 1 on the optical sense form.
2. Manganese metal must absorb radiation with a minimum frequency of 2.15 x 1015 s-1 before it can emit
an electron from its surface via the photoelectric effect. What is the minimum energy (in J) needed for
emission of one electron from manganese?
A) 3.08 x 10–49
B) 1.43 x 10-21
D) 3.24 x 1048
E) 1.43 x 10-18
C) 1.43 x 10-15
3. What is the de Broglie wavelength associated with an electron traveling at 0.125 times the speed of light?
A) 1.94 x 10-2 nm
B) 194 nm
C) 1.94 x 10-4 nm
D) 1.26 x 10-2 nm
E) 1.33 x 10-3 nm
4. Which of the following molecules or ions has a (have) multiple bond(s) in its (their) Lewis structure(s)?
i. NO+
A) i
ii. PF3
B) iii
C) iv
iii. SCl2
iv. HCN
D) i and ii
E) i and iv
5. Which set of quantum numbers CANNOT occur together to specify an orbital?
A) n = 2, ℓ = 1, mℓ = -1
B) n = 3, ℓ = 3, mℓ = 2
C) n = 3, ℓ = 2, mℓ = 0
D) n = 4, ℓ = 3, mℓ = -1
E) n = 5, ℓ = 4, mℓ = 4
6. What is the maximum number of electrons in an atom that can have the principal quantum number n = 4?
A) 4
B) 8
C) 18
D) 32
E) 34
Chemistry 101, Mid-Term Test 1
Version A
7. The Heisenberg uncertainty principle states that:
Page 3 of 8
A) There is an uncertainty in the order of filling the 4s and 3d orbitals when writing the electron
configurations in the periodic table.
B) There is uncertainty in knowing the energy of an electron so the wave function has to be squared (ψ2)
to obtain the probability density.
C) There is uncertainty in knowing the position and momentum of the electron simultaneously.
D) There is an uncertainty in the position of the electron in a 2s orbital because there is a node in the
radial probability density function
E) There is an uncertainty in obtaining the wave length of a macroscopic particle.
8. Which of the following represents a possible electron configuration for an EXCITED STATE of the
oxygen atom (O)?
A) [He]2s22p4
9.
B) [He]2s22p43s1
C) [He]2s24p1 D) [He]2s32p3
E) [He]2s22p33s1
If A > B means that the ELECTRONEGATIVITY of A is greater than that of B, which inequality is
FALSE?
A) N > C
B) As > S
C) C > Ge
D) N > Ge
E) Li > Cs
10. Which of the following electron configurations represents the ground state of arsenic (As)?
A) [Ar]4s24d104p3
B) [Kr]4s23d104p3
D) [Ne]3s23p6
E) [Ar]4s23d103p3
C) [Ar]4s23d104p3
11. Which of the following ionic substances has the greatest lattice energy?
A) AgCl
B) CuO
C) CrN
D) LiCl
E) CsI
12. Which of the following ions has/have an electron configuration in which all of the occupied subshells
are completely filled?
(i) Ti+2
(ii) Ga +3
A) i only
B) ii only
(iii) P–3
C) i, ii and iii
D) iii only
E) ii and iii
Chemistry 101, Mid-Term Test 1
Version A
Page 4 of 8
13. If A > B means that the radius of A is greater than the radius of B, then which of the
following is INCORRECT?
A) Mg2+ > Al3+
B) F– > F
C) Ca > Ca2+
D) Cl > I
E) Rb > K
14. Which one of the following statements about the quantum mechanical model
of the atom is INCORRECT?
A) Atomic orbitals describe regions in which an electron is most likely to be found around a nucleus.
B) The three electrons in the configuration 2p3 have parallel spins (i.e. the same ms value).
C) The fact that two electrons in the same atom cannot have the same set of four quantum numbers
n, ℓ, mℓ, ms means that each orbital can have only one electron.
D) The velocity of all electromagnetic radiation equals the speed of light.
E) Photons of only certain allowed frequencies can be absorbed or emitted as the electron changes
energy state
15. Which of the following molecules has the most polar type of bonds?
A) SCl2
B) SF2
C) S8
D) PF3
E) NF3
16. Which one of the following responses contains the correct order (from largest to smallest) of effective
nuclear charge (Zeff)?
A. Li > Be > B
B. C > F > Na
C. Na > Be > Li
D. B > Be > N
E. Al > Na> Mg
Chemistry 101, Mid-Term Test 1
Version A
Page 5 of 8
PART II – Written Answers to Questions. [Total Marks = 20]
Write your answers directly on this test paper. Show all your work. Hand in the entire test
paper at the end of the test period.
1. (a) [2 MARKS] Clearly indicate and label the areas for the s block, the p block, the d block and the f
block in the blank periodic table below.
C
s
s
s
s
s
s
s
d
d
s
s
d
d
s
s
p p
p
p
p p
p p
p
p
p
p
p
d
d
d
d
d
d
d
d
d
d d
d
d
p
s
d
d d
d
d
d
d
d
d
p
s
d
d
d
d
d
d
d
d
d
f
f
f
f
f
f
f
f
f
f
d
f
f
d d
B
s
p p
p
p
p
p
p
p p
p
p
p
p
p
p
f
f
f
f
f
f
f
f
f
f
f
f
f
f
f
f
(b) [1 MARK] Briefly explain, in terms of electrons, why the s block has a different number of columns
(groups) than found in the p block.
It takes only two electrons to fill an s-orbital, whereas it takes six electrons to fill a set of three porbitals. Therefore the s-block is two elements wide and the p-block is six elements wide.
(c) [1 MARK] Label with a capital B the column (group) that contains the elements with the largest negative
electron affinity values (that is, the elements most likely to form a -1 ion).
B labels the halogens, group 7A or 17.
(d) [1 MARK] Label with a capital C the column (group) that corresponds to the generalized electron
configuration: [noble gas] ns2 (n-1)d10 np1
C labels the first group of the p-block, group 3A or 13.
Chemistry 101, Mid-Term Test 1
Version A
Page 6 of 8
2. Consider the energy levels in the hydrogen atom as diagrammed below. Answer the following
questions about the hydrogen atom. (The arrows, except the energy axis on the left, represent
possible electron transitions.)
n=5
n=4
Energy
E
n=3
B
n=2
D
n=1
A
C
(a) [3 MARKS] Calculate the energy change corresponding to the transition labeled D. Express your
answer in kJ mol–1.
For one electron ΔH = –2.18 × 10–18 J (( 1/n2f) – (1/n2i)) (This formula is on the data sheet.)
ΔH = –2.18 × 10–18 J ((1/52) – (1/22)) = –2.18 × 10–18 J × (– 0.21) = 4.578 × 10–19 J
To get the energy change for exciting a mole of electrons we multiply this number by the
Avogadro constant.
For a mole ΔH = 4.578 × 10–19 J ×6.02 × 1023 mol–1 = 2.76 × 105 J mol–1
ΔH = 276 kJ mol–1
(b) [1 MARK] Which transition from among the ones shown represents the lowest-frequency emission
for an electron returning to the ground state?
C
Chemistry 101, Mid-Term Test 1
Version A
Page 7 of 8
3. Consider the second and third quantum numbers, the azimuthal (ℓ) and magnetic (mℓ) quantum
numbers, respectively. (Note: The azimuthal quantum number is also known as the angular
momentum or subsidiary quantum number.)
(a) [2 MARKS] Give a short explanation of the physical meaning of each of these two quantum
numbers.
The azimuthal quantum number (ℓ) describes the shapes of the orbitals.
The magnetic quantum number (mℓ) describes the orientation of the orbitals.
(b) [1 MARK] Give the range of allowed values for any one of these two quantum numbers. (If you
give both, only the first one will be marked.)
The azimuthal quantum number (ℓ) can have integral values from 0 to n-1 for each value of n.
OR
The magnetic quantum number (mℓ) can have integral values between – ℓ and + ℓ, including zero.
4. (a) [1 MARK] If core electrons were perfect at screening valence electrons from the nuclear charge,
what would be the effective nuclear charge (Zeff) „experienced by‟ the 4s valence electron of
potassium (K)?
Z – core electrons = 19-18 = 1
(b) [1 MARK] The actual value is 3.5. Explain the discrepancy between this value and your answer in
part (a)..
The 4s electron of potassium “has a small probability of being found close to the nucleus and
inside the core electrons.” (text page 264)
Or, alternatively, the student can say that core electrons are not 100% effective at screening.
5. (a) [1 MARK] Arrange the following atoms in order of increasing first ionization energy (I1): (i.e.
smallest to largest)
Ne, Na, Mg, Al, Cl
Na < Al < Mg < Cl < Ne
Chemistry 101, Mid-Term Test 1
Version A
Page 8 of 8
6. [2 MARKS] Write out the full electron configuration (i.e. not the condensed electron configuration)
for the cobaltous ion Co2+.
Co is 1s22s22p63s23p63d74s2 Then remove the outer two electrons to give the correct charge.
Co2+ is this 1s22s22p63s23p63d7
7. [3 MARKS] Draw all possible resonance structures for the nitrous acid molecule HONO that obey
the octet rule for all atoms (except H, of course). (The atoms are connected in the order given.) Show
non-bonding electrons as dots (: ) and bonding electron pairs as lines (–). Show all non-zero formal
charges on all atoms for all structures. Put a circle around the structure(s) that best represent the
electron distribution in the real nitrous acid molecule.
(There are 18 valence electrons.)
H
O
N
O
H
END
O
N
O