Problem Set 4 Chemistry
Answer Key Chapter 8 and 9 Bonding
nd
Due Friday March 22
Test Tuesday March 26th
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:
..
Ionic Compounds
21) Describe and diagram the process by which a neutral sodium atom becomes
positively charged.
Na.  Na+1 + 1eThe sodium atom gives up one electron to form the Na+1 cation
22) Describe and diagram
the
..
.. process by which a neutral chlorine atom becomes
negatively charged.
.
..
1e- + :Cl:  :Cl:
The chlorine atom gains one electron to form the Cl-1 anion.
23) What do atoms of a metal do to become a positively charged ion? What are these
positively charged ions called? Atoms of a metal will give up some or all of
their valence electrons to become positively charged. They have a positive
charge because there are more protons than electrons in the new ion. These
ions are called cations.
24) What do atoms of a non-metal do to become a negatively charged ion? What are
these negatively charged ions called? Atoms of a non-metal will gain electrons
to fill their valence energy level to become negatively charged. They have a
negative charge because there are more electrons than protons in the new
ion. These ions are called anions.
25) Describe the concept of electroneutrality and how it applies to ionic crystals.
Electroneutrality states that the overall number of electrons must be
maintained in any compound. The electrons that were on metals are
transferred to the non-metals to create the different charges of the ions. The
oppositely charged particles attract each other to form solid crystals.
26) What is lattice energy and how is it involved in an ionic bond? Lattice energy is
the energy required to separate the ions of an ionic compound wand is the
energy given off when positive and negative ions attract. An ionic bond is
formed when anions and cations attract each other.
27) What do the subscripts in a chemical formula tell you about the makeup of the
ionic compound?
The subscripts show the lowest whole number ratio of ions in a neutral ionic
compound. Ex: The ratio of sodium cations to oxide anions is 2 to 1 in sodium
oxide, Na2O.
28) Why are roman numerals used to name some ionic compounds, like copper (II)
chloride, but not used to name others, like sodium chloride? The roman
numerals are used to indicate the charge of the cation in any ionic compound
that has a metal that can take multiple oxidation states. Many ionic
compounds have cations that take only one oxidation state, and that value
does not need to be represented with a roman numeral.
29) Using the concepts of ionic radii and lattice energy account for the trend in
melting points shown in the following table:
Ionic
Melting Lattice
Ionic Radii
As the ionic radius of non-metal anions
Compound Point
Energy
increases (F-1  I-1), the melting point
o
+1
KF
858 C -808 kJ/mol K = 138 pm, and lattice energy decrease. The
larger the ion, the less energy is needed
F-1 = 133 pm
o
KCl
770 C -740 kJ/mol K+1 = 138 pm, to hold the substance in a solid phase,
or in a crystalline structure.
Cl-1 = 181 pm
o
KBr
734 C -671 kJ/mol K+1 = 138 pm,
Br-1 = 195 pm
o
KI
681 C
-632 kJ/mol K+1 = 138 pm,
I-1 = 220 pm
30) What subscripts would be used if an ionic compound was formed…
a. Between an alkali metal and a halogen 1:1
b. Between an alkaline earth metal and a halogen 1:2
c. Between an alkali metal and the oxide anion 2:1
d. Between an alkaline earth metal and an oxide anion 1:1
e. Between a group 3A element and a halogen.1:3
31) Name this binary ionic compound: K2S potassium sulfide
32) Name this binary ionic compound: NbN niobium (III) nitride
33) Give the formula for the binary ionic compound: calcium fluoride CaF2
34) Give the formula for the binary ionic compound: gold (II) chloride AuCl2
35) Name this ternary ionic compound: Cd2SiO4 cadmium silicate
36) Name this ternary ionic compound –Ni(NO3)3 nickel (III) nitrate
37) Why is it important to be able to name compounds correctly? Naming
correctly identifies the substances in a reaction, or a medicine,
without proper names, compounds could be confused, leading to
problems.
38) Why is being able to write the formulas for compounds important? Creating
formulas correctly identifies the substances in a reaction, or a medicine,
without proper names, compounds could be confused, leading to problems.
39)
Compare AND contrast binary ionic compounds to ternary ionic compounds.
Binary ionic compounds have only two elements, while ternary ionic
compounds have more than two elements. They are both ionic compounds,
with a cation and an anion that are held together through coulombic attraction.
(opposite charges attract).
40)
Why are parenthesis used in writing a formula of an ionic compound with a
polyatomic ion? For example, the formula for calcium hydroxide is Ca(OH)2.
Parenthesis help isolate the polyatomic ion, showing that it is an individual ion,
but there must be more than one of them in the compound to need parentheses.
41)
Define a metallic bond. How does it differ from an ionic bond? Metallic bonds
utilize the sea of electrons that metals have between their cations to hold the
ions in place, while allowing some sliding and shifting. This mobility is far
different from ionic bonds because crystalline structures of ionic compounds
are very rigid and far less mobile than the particles in a metal.
42)
Why does an applied force (like hitting a piece of metal with a hammer) cause
metal ions to move? The applied force allows the metal ions to move because the
ions are not strictly confined by bonds. The metallic bonds between the ions are
mobile. This allows most metals to be malleable and ductile. What unique
properties of metals are due to this mobility? they are shiny, conductive, ductile,
and malleable because of these mobile electrons.
Acids
43) 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.
44) 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
45) 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
46) 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-).
1) Identify the following as:
binary acids (BA)
ternary acids (TA)
molecular compounds (MC).
binary ionic compounds (BIC)
ternary ionic compounds (TIC)
ionic compounds with multiple charge metals (ICMC)
a) CO2
b) H2SO4
c) LiI
d) Be(NO2)2 e) MoO
f) HCl
MC
TA
BIC
TIC
ICMC
BA
g) MoO2
h) MgCl2
i) Sr(NO3)2 j) (NH4)2O
k) HBr
l) NaF
ICMC
BIC
TIC
TIC
BA
BIC
m)C6H12O6 n) H2CO3
o) FeCl6
p) CH2O
q) TiCl4
r) PbO
MC
TA
ICMC
MC
ICMC
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
h. copper (I) oxide Cu2O
b. iron (III) oxalate Fe2(C2O4)3
i. beryllium hydroxide Be(OH)2
c. perchloric acid HClO4
j. sulfur hexabromide SBr6
d. rubidium sulfide Rb2S
k. magnesium oxide MgO
e. carbon tetrachloride CCl4
l. acetic acid HC2H3O2
f. hydrochloric acid HCl
m. diphosphorous pentoxide P2O5
g. sulfuric acid H2SO4
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)