Problem Set 3c Chemistry
Answer Key Chapter 9 Bonding
th
Due Friday November 12
Test Tuesday November 16th
Molecular compounds
1) What makes molecular compounds different from ionic compounds? Which elements are
typically found in molecular compounds? Molecular compounds are formed when
electrons between two non-metals (or hydrogen) are shared. There is no transfer of
electrons in a molecular compound. Also – each molecule of substance exists alone –
the ionic crystals are connected one to the next, that is not true of molecules. The
non-metals are found in molecules.
2) How many electrons are shared in…
a. A single covalent bond 2
b. A double covalent bond 4
c. A triple covalent bond 6
d. A quadruple covalent bond 8
e. A coordinate covalent bond 2
3) What happens to bond length as more and more electrons are shared in a bond?
Which is a longer bond: a single bond, a double bond or a triple bond? Why?
As more and more electrons are added to a bond, the nuclei of the atoms in
the bond are drawn closer and closer together. This decreases the bond
length and the energy of the bond increase. A triple bond will be the shortest
measured bond assuming the atomic radii are similar in value.
4) What is a sigma () bond? What is a pi () bond? A sigma bond occurs when
an s orbital overlaps with another s orbital or with a p orbital. A pi bond
occurs when two p orbitals overlap. Overlapping orbitals show which two
electrons are being shared.
5) Name the following molecular compounds:
a. carbon dioxide a. CO2
b. phosphorous tribromide b. PF3
c. silicon tetrabromide c. SiBr4
d. dinitrogen tetroxide d. N2O4
e. phosphorous pentachloride e. PCl5
6) Give the formula for the following molecular compounds:
a. sulfur dioxide SO2
d. diselenium heptoxide Se2O7
b. nitrogen triiodide NI3
e. chlorine heptabromide ClBr7
c. carbon monoxide CO
f. carbon tetrachloride CCl4
7) Why is the formula for “tricarbon monophosphourous monoxide” of great
cinematographic importance for sci-fi films? C3PO, the gold robot in Star Wars
8) How many atoms of nitrogen are there in a molecule of TNT: C6H3(NO2)3? 3
9) Draw the Lewis Dot diagram for these elements: C, N, O, F
.
.
.
..
.C.
.
:N
:O:
:F:
.
.
.
.
10) Draw the Lewis Dot Diagram for these molecular compounds. The underlined
elements are the central atom in the molecule.
a. Cl2
b. H2S
c. CH2Cl2
d. SiS2..
:Cl:
.. ..
..
..
..
|
a. :Cl-Cl:
b
H-S-H
c.
H
–
C
–
H
d.
S=Si=S
.. ..
..
..
..
|
:Cl:
..
11) What is a coordinate covalent bond? Explain how carbon monoxide is able to
follow the octet rule even though carbon only has four valence electrons and a
quadruple bond is not formed. A coordinate covalent bond is a chemical bond
between two atoms where one atom donates the two electrons to be shared in
the bond – it is still a covalent bond because once donated the two electrons
are shared by the two atoms. Carbon monoxide forms a coordinate covalent
bond because carbon only has 4 valence electrons and oxygen has 6 – there is
a triple bond formed (one sigma and two pi bonds) – the second pi bond’s
electrons both came from the oxygen atom.
:C=O:
12) What are resonance structures? Resonance structures are drawings of the
possible arrangements of the pi bonds in a compound. The molecule actually
switches very quickly (resonates) between its different resonance structures.
13) Draw at the correct resonance structures of …
a. Ozone (O3)
b. Carbonate (CO3-2)
.. .. ..
:O-O=O:
..
.. .. ..
:O=O-O:
..
c. Sulfate (SO4-2)
..
..
.x
..
-2
:O:
-2
:O:
-2
:O:
-2
:O:
.. | ..
.. | ..
.. | .x
.. | ..
:O-C=O:
:O=C-O:
:O-S-O:
:O-S-O:
..
..
.. | ..
.. .x
:O:
-2
:O:
:O:
.. || ..
..
..
.x
.x
:O-C-O:
:O:
:O:
-2
..
..
.x | .x
.. | .. -2
:O-S-O:
:O-S-O:
.. | ..
.. | ..
:O:
:O:
..
.x
note – SO4-2 are all the same
tetrahedron with two extra e- =“x”
14) Use the chart of electronegativities to determine if the following compounds have
ionic bonds, polar covalent bonds, or non-polar covalent bonds.
a. H and O polar covalent
d. Si and B non-polar covalent
b. As and P non-polar covalent
e. Ca and O ionic
c. C and Cl polar covalent
15) Draw the electron density cloud for these molecular compounds.
a. H2
b. HCl
c. H2O
d. CCl4
O
H-H
H-Cl
H
H
Cl
Cl C Cl non-polar
Cl
16) What does the electron density cloud represent? The electron density cloud
represents the electron orbitals after they have formed covalent bonds. Polar
covalent bonds will appear as asymmetric clouds, while non-polar covalent
bonds will have perfect symmetry as a shape.
17) What do the letters VSEPR stand for in VSEPR theory? Valence Shell Electron
Pair Repulsion - this theory suggests that the valence electron pairs in a
compound will repel other pairs because both pairs will have negative
charges.
18) What is a tetrahedron? How is it possible to describe CH4, NH3 and H2O as
having a tetrahedral electronic geometry? Draw each molecule as a 3-D figure.
A tetrahedron is a symmetric four sided 3-dimensional form. All three of
those molecules have four pairs of electrons off the central atom and
therefore the electronic geometry is tetrahedral, but the molecular geometry
will be: CH4 – tetrahedral, NH3 – trigonal pyramidal, H2O – linear bent
H
C
H HH
..
N
H HH
.. ..
O
H H
19) Why is the bond angle in water (106o) smaller than the bond angle in methane
(109.5o) if they both have tetrahedral electronic geometries? The 2 lone pairs of
electrons off the central oxygen atom force the 2 pairs bonded electrons
between the oxygen and hydrogen towards each other (away from the nonbonded electron pairs). In methane the bonds repel each other equally.
20) Draw an appropriate 3-D drawing based upon the VSEPR theory for…
See page 260 for text images
a. BeCl2 linear c. BF3 trigonal planar
e. carbon tetrachloride
tetrahedral
..
..
..
..
..
:Cl-Be-Cl:
:F
F:
:Cl:
..
..
..
..
B
C
:Cl:
.. :Cl:
.. :Cl:
..
:F:
..
b. Ammonia
Trigonal pyramidal
..
N
H HH
d. water
linear bent
.. ..
O
H
H
f. sulfur hexachloride
octahedral
..
.. :Cl: ..
:Cl
Cl:
..
..
S
:Cl:
:Cl:
..
..
:Cl:
..
Acids
21) Discuss acids and bases in a couple of sentences. Be sure to explain the following
topics in specific, scientific terms: Acids and bases are ionic compounds that
are identified by their ions. Acids, as we know them now, have a hydrogen
cation. Bases, as we know them now, have hydroxide as their anion.
a) The prefix and the suffix of binary acids: A binary acid, like HCl, is named
hydro-chlor-ic acid. The prefix “hydro-” shows that the acid is a binary
substance, and the “-ic” suffix shows that the substance is an acid.
b) Why “ates are icky” or where the “termites are in your house and not in
your ate-ic (attic).” The odd phrases “ates are icky” and “termites are
in your house and not in your ate-ic.” Are meant to serve as verbal
reminders of how the ternary acids are named. If the polyatomic
anion ends with “-ate” the acid ends with “-ic”, while if the polyatomic
anion ends with “-ite” the acid ends in “-ous.”
c) how the name can be translated into the correct formula Changing from a
name of an acid or a base to its formula follows the principle of
electroneutrality. Because acids and bases are ionic compounds, the
overall charge on the compounds must be neutral, so the cations
charge will be equal and opposite the anions charge.
d) specifically how a ternary acid, like H2SO3, is named. To name H2SO3 the
name of the anion SO3-2 is sulfite so the name of the acid is sulfous acid.
22) Give the formula for each of the following acids
a) hydrochloric acid HCl b) hydrophosphoric acid H3P
d) nitrous acid
HNO2
c) carbonic acid H2CO3
23) Give the name for each of the following acids and bases.
a) HI-hydroiodic acid
b) H2SO3 sulfous acid
c) HC2H3O2 acetic acid
d) H2Se hydroselenic acid e) LiOH lithium hydroxide
24) Compare and contrast hypochlorous acid (HClO) with perchloric acid (HClO4) in
as much detail as possible. Both are ternary ionic compounds. The chlorine
atom in the hypochlorous acid has only one oxygen atom – this is one less
than the number of oxygen atoms in chlorous acid (hence the hypo-). The
chlorine atom in the perchloric acid has four oxygen atoms one more than
the number of oxygen atoms in chloric acid (hence the per-).
REVIEW REVIEW
REVIEW REVIEW REVIEW
1) Identify the following as:
binary acids (BA)
ternary acids (TA)
binary ionic compounds (BIC)
REVIEW
molecular compounds (MC).
ternary ionic compounds (TIC)
ionic compounds with multiple charge metals (ICMC)
a) CO2
MC
b) H2SO4
TA
c) LiI
BIC
d) Be(NO2)2
TIC
e) MoO
ICMC
f) HCl
BA
g) MoO2
ICMC
h) MgCl2
BIC
i) Sr(NO3)2
TIC
j) (NH4)2O
TIC
k) HBr
BA
l) NaF
BIC
m)C6H12O6
MC
n) H2CO3
TA
o) FeCl6
ICMC
p) CH2O
MC
q) TiCl4
ICMC
r) PbO
ICMC
2) True Formula Test… give the formula of each of the following substances…
there are molecular compounds, binary ionic compounds, ternary ionic
compounds and roman metal compounds all mixed in… good luck
a. potassium nitrate KNO3
b. iron (III) oxalate Fe2(C2O4)3
c. perchloric acid HClO4
d. rubidium sulfide Rb2S
e. carbon tetrachloride CCl4
f. hydrochloric acid HCl
g. sulfuric acid H2SO4
h. copper (I) oxide Cu2O
i. beryllium hydroxide Be(OH)2
j. sulfur hexabromide SBr6
k. magnesium oxide MgO
l. acetic acid HC2H3O2
m. diphosphorous pentoxide P2O5
n. hydrogen hydroxide H2O
obviously answers will vary for these last 6 questions.
3) binary ionic compound. Example lithium iodide LiI (metal and a nonmetal)
4) ionic compound. Example Lithium iodate LiIO3 (metal and polyatomic
anion or two polyatomic ions or ammonium and a non-metal)
5) Roman Metal compound. Example Tin (II) oxide SnO (any metal with
multiple oxidation states and any anion)
6) molecular compound. Example Carbon disulfide CS2 any two non-metals
7) Write the name and formula of any binary acid hydrochloric acid HCl
(hydrogen cation and any non-metallic anion)
8) Write the name and formula of any ternary acid. Chloric acid HClO3
(hydrogen and any polyatoimic anion)