CHM 2045C Module 4 Part I Sample Exam  Answers

Ga3+.

Explanation:
Ga3+ : [Ar] 3d10

Solution Reference:
Page 373, Valence Electrons

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 1 + 2 + 3 + 4 + 5.

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

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

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

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

SF4

Explanation:
S has 10 valence electrons around it.

Solution Reference:
Page 383, the Octet Rule

18.

Explanation: Solution Reference:
Page 383, The Octet Rule

26.

Explanation: Solution Reference:
Page 383, The Octet Rule

11.

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

NO3-

Explanation:
Find two species with the same number of valence electrons or draw the Lewis structures. Solution Reference:
Page 382, Covalent Bonding

2.

Explanation: Solution Reference:
Page 382, Covalent bonding

2.

Explanation: Solution Reference:
Page 382, Covalent Bonding

1.

Explanation: Solution Reference:
Page 382, Covalent Bonding

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.

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

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

0 and +6. Explanation: Solution Reference:
Page 406, Formal Charges on Atoms

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

NH4+.

Explanation: Solution Reference:
Page 413, Molecular Shapes

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

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

H2S

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

Solution Reference:
Page 423, Molecular Polarity