Chemistry 121
Fall 2014
Exam Four
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I will not share information about the material presented on or required for this exam with
anyone until the exam is graded and returned to me.
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1. Multiple choices (3 points each, 45 points total)
1) Which of the following statements is TRUE?
A) A covalent bond is formed through the transfer of electrons from one atom to another.
B) A pair of electrons involved in a covalent bond are sometimes referred to as "lone pairs."
C) It is not possible for two atoms to share more than two electrons.
D) Single bonds are shorter than double bonds.
E) A covalent bond has a lower potential energy than the two separate atoms.
2) Place the following elements in order of increasing atomic radius.
P
Ba
Cl
A) Ba < P < Cl
B) P < Cl < Ba
C) Cl < P < Ba
D) Cl < Ba < P
E) Ba < Cl < P
3) Place the following in order of decreasing radius.
I–
Xe
Cs+
Ba2+
A) I– > Xe> Cs+> Ba2+
B) Ba2+> Cs+> Xe > I–
C) Cs+> Ba2+> Xe > I–
D) Xe > I– > Cs+> Ba2+
E) I– > Xe> Ba2+> Cs+
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4) Which reaction below represents the second ionization of Sr?
A) Sr(g) → Sr+ (g) + e–
B) Sr2+ (g) + e– → Sr+ (g)
C) Sr+ (g) + e–⁻ → Sr(g)
D) Sr– (g) + e– → Sr2– (g)
E) Sr+ (g) → Sr2+ (g) + e–
5) Place the following in order of increasing first inonization energy.
N
F
A) N < As < F
B) As < N < F
C) F < N < As
D) As < F < N
E) F < N < As
As
6) Which of the following reactions is associated with the lattice energy of RbI (ΔH°latt)?
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A) Rb(s) + I2(g) → RbI(s)
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B) RbI(s) → Rb⁺(g) + I⁻(g)
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C) RbI(s) → Rb(s) + I2 (g)
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D) RbI(s) → Rb⁺(aq) + I⁻(aq)
E) Rb⁺(g) + I⁻(g) → RbI(s)
7) Place the following in order of increasing magnitude of lattice energy.
MgO
KI
CaS
AlN
A) CaS < MgO < AlN < KI
B) KI < CaS < MgO < AlN
C) MgO < CaS < KI < AlN
D) KI < MgO < CaS < AlN
E) AlN < MgO < CaS < KI
8) Place the following elements in order of increasing electronegativity.
Sr
N
Na
A) Sr < Na < N
B) Na < N < Sr
C) Sr < N < Na
D) N < Sr < Na
E) N < Na < Sr
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9) Using periodic trends, place the following bonds in order of increasing ionic character.
Si-P
Ge-S
Si-S
Ge-Cl
A) Si-P < Ge-Cl < Ge-S < Si-S
B) Si-P < Si-S < Ge-S < Ge-Cl
C) Ge-Cl < Ge-S < Si-S < Si-P
D) Si-P < Ge-S < Ge-Cl < Si-S
E) Si-P < Ge-S < Si-S < Ge-Clr
10) Choose the bond below that is most polar.
A) C-N
B) C-F
C) Si-O
D) Si-F
E) F-F
11) Which molecule or compound below contains a pure covalent bond?
A) Li2CO3
B) SCl6
C) Cl2
D) PF3
E) NaCl
12) How many of the following elements can form compounds with an expanded octet?
I
O
Cl
Xe
A) 2
B) 0
C) 3
D) 1
E) 4
13) Choose the paramagnetic species from below.
A) Ca
B) O2–
C) Cd2+
D) Zn
E) Nb3+
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14) Which reaction below represents the electron affinity of Li?
A) Li(g) + e⁻ → Li⁻(g)
B) Li(g) → Li⁺(g) + e⁻
C) Li(g) + e⁻ → Li⁺(g)
D) Li⁺(g) → Li(g) + e⁻
E) Li⁺(g) + e⁻ → Li(g)
15) Which of the following elements has the greatest (most negative) electron affinity.
a) Ne
b) Cl
c) Br
d) P
e) Mg
2. (10 pts) Draw Lewis structures for the following. You must show all lone pairs.
a) N2F2 (skeletal structure FNNF)
b) SeCl5 -1
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3. (8 pts) This question explores the bonding and properties of the cyanide ion, CN-1
a) Draw Lewis structure of CN-1.
b) In aqueous solution, CN-1 reacts with H+ to form a weak acid. Should the formula of this acid
be written HCN or HNC? Explain your reasoning, using drawings if needed.
4. (13 pts) a) Give the ground state electron configuration for Se2–.
b) Give the ground state electron configuration for Cr.
c) Briefly explain why Mn (Manganese) often exhibits oxidation states of +2 and +7.
d) Select (circle) the highest second ionization energy element:
Na
Mg
Al
e) Select (circle) the lowest first ionization energy element:
Se
As
Cl
Br
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5. (18 points) (a) Draw all possible resonance structures for N2O (skeletal structure NNO)
(b) Assign formal charges to each resonance structure (show work). Can you eliminate any of the
resonance structure on the basis of formal charge? Why and why not?
(c) Given the following bond lengths and your answer above, explain why the bond length of NN in N2O is 113 pm and the bond length of N-O is 119 pm.
N-N 167 pm
N=N 120 pm
N=N 110 pm
N-O 147 pm
N=O 115 pm
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6. (6 pts) An article "Synthesis of a new chemical element with atomic number Z=117" was
published in Physical Review Letters on 5 April 2010. This element was then named as
Ununseptium (Uus).
a) Could you predict what other elements will Uus most closely resemble in terms of its
chemistry
b) What are four possible quantum numbers for the last electron added to element 117 (Uus)?
c) What do you predict to be the formula of this compound element 117 would form with Al
(you may use X to represent Uus)?
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