CHM 2045C Module 4 Part I Sample Exam  Answers

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1.

The correct answer is:
Ga3+.

Explanation:
Ga3+ : [Ar] 3d10

Solution Reference:
Page 373, Valence Electrons



 

2.* The correct answer is:
5.

Explanation:
The crystal lattice energy is the energy given off in the formation of one mole of solid NaCl from the combination of one mole of Na+(g) with one mole of Cl-(g).

Solution Reference:
Page 379, Lattice Energy



 

3.* The correct answer is:
1 + 2 + 3 + 4 + 5.

Explanation:


Solution Reference:
Page 379, Lattice Energy
* Will not be on test



 

4. The correct answer is:
NaF

Explanation:
The crystal lattice energy U is proportional to the charges on the ions and inversely proportional to the size of the ions or distance between the ions.


Solution Reference:
Page 379, Lattice Energy



 

5. The correct answer is:
NaF

Explanation:
There is a correlation between the melting point and the crystal lattice energy. The larger the lattice energy, the higher the melting point.

Solution Reference:
Page 379, Lattice Energy

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6. The correct answer is:
Ca+.

Explanation:
Calcium is in family 2, so we would expect the calcium ion to be 2+ so that is has a noble gas configuration.

Solution Reference:
Page 377, Bonding in Ionic Compounds



 

7. The correct answer is:
H

Explanation:
Since hydrogen is from the first period, the maximum number of electrons it can have is two.

Solution Reference:
Page 383, The Octet Rule



 

8. The correct answer is:
SF4

Explanation:
S has 10 valence electrons around it.

Solution Reference:
Page 383, the Octet Rule



 

9. The correct answer is:
18.

Explanation:


Solution Reference:
Page 383, The Octet Rule



 

10. The correct answer is:
26.

Explanation:


Solution Reference:
Page 383, The Octet Rule

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11.

The correct answer is:
32.

Explanation:
This problem involves two steps as it is necessary for a student to know the formula of the perchlorate ion, ClO4-.


Solution Reference:
Page 383, The Octet Rule



 

12. The correct answer is:
NO3-

Explanation:
Find two species with the same number of valence electrons or draw the Lewis structures.


Solution Reference:
Page 382, Covalent Bonding



 

13. The correct answer is:
2.

Explanation:


Solution Reference:
Page 382, Covalent bonding



 

14. The correct answer is:
2.

Explanation:


Solution Reference:
Page 382, Covalent Bonding

 

15. The correct answer is:
1.

Explanation:


Solution Reference:
Page 382, Covalent Bonding

 

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16. The correct answer is:
that have no suitable single Lewis electron-dot formula.

Explanation:
The actual distribution of electrons which cannot be depicted by a single Lewis structure is an average of the various Lewis structures that can be drawn for a molecule or ion.

Solution Reference:
Page 392, Resonance


Module 7 Questions 17-18

17.

The correct answer is:
HBr(g) --> H(g) + Br(g)

Explanation:
The bond dissociation energy is the energy required to break a gaseous molecule into gaseous atoms.

Solution Reference:
Page 402, Bond Energy

 

18. The correct answer is:
473.

Explanation:

NF3(g) --> N(g) + 3F(g)  DH = 841 kJ
FN = NF --> 2N(g) + 2F(g)
DH = 1033 kJ

The average N-F bond energy is 841/3 = 280 kJ.



Solution Reference:
Page 402, Bond Energy

Module 4 Part II Questions #19-25

19. The correct answer is:
0 and +6.

Explanation:


Solution Reference:
Page 406, Formal Charges on Atoms



20. The correct answer is:
trigonal bipyramidal and linear.

Explanation:
Five pairs of electrons are equivalent to a trigonal bipyramidal arrangement of the electrons. Repulsions are minimized by having three lone pairs of electrons in the trigonal plane.

Solution Reference:
Page 413, Molecular Shapes

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21. The correct answer is:
NH4+.

Explanation:


Solution Reference:
Page 413, Molecular Shapes



 

22. The correct answer is:
OSO.

Explanation:

The lone pair of electrons on sulfur causes a bent molecule. In all the other molecules in this question, the central atom does not have any lone pairs of electrons (only bonding pairs). Two regions of electron density about each central atom.


Solution Reference:
Page 413, Molecular Shapes



 

23. The correct answer is:
SO3.

Explanation:
All of the central atoms in the other molecules have a lone pair of electrons except sulfur.

Solution Reference:
Page 413, Molecular Shapes



 

 

24. The correct answer is:
H2S

Explanation:
H2S is an angular molecule and the sulfur atom has two lone pairs of electrons.

Solution Reference:
Page 423, Molecular Polarity



 

25. The correct answer is:
PF5

Explanation:
PF5 is the only symmetrical molecule.

Solution Reference:
Page 423, Molecular Polarity

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