Download Chapter 21 Chapter 21 Nonmetallic Elements and Their

Chapter 21
Nonmetallic Elements and Their Compounds
This chapter is a general review of the nonmetallic elements
and their compounds. Upon completion of this chapter, your
students should be able to:
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List ten non-metal compounds that are gases at room
temperatures.
Write balanced equations that describe three different methods
for the production of hydrogen gas.
List three broad types of hydrides and describe the physical
characteristics of each.
Name the three isotopes of hydrogen and indicate the number of
protons and neutrons found in the nucleus of each.
Describe two methods for the separation of H2O and D2O.
Define hydrogenation and describe the importance of this
process in the food industry.
Describe what is meant by the hydrogen economy and list
various approaches being examined for the production and
storage of hydrogen.
Name two allotropes of carbon and indicate which one is most
thermodynamically stable at room temperature.
State why acids should never be mixed with metal cyanides
without proper ventilation.
State the property of solid carbon dioxide that is responsible
for it to be referred to as dry ice.
Write the chemical formula for ammonia and hydrazine and list
the principle use of each.
Compare the physical effect of N2O and NO2 on humans.
Describe how aqua regia is prepared and state what a common
use of this solvent is.
State what the difference is in molecular structure for white
phosphorous and red phosphorous.
Write the formula for phosphoric acid and identify it as being
either a strong or weak acid.
State the oxidation number of oxygen in oxide, peroxide and
superoxide.
Describe the change in acidic character of oxides going from
left to right for third-period elements.
List beneficial uses of ozone.
Name and give the formula for the world’s most important
industrial chemical.
State four ways how the chemistry of fluorine differs from the
rest of the halogens.
Describe the chlor-alkalic process for the production of
chlorine gas and indicate a potential pollution hazard as a
result of this process.
State the property of HF that makes it difficult to store.
Provide four examples of how halogen-containing compounds are
used.
Section 21.1
General Properties of Nonmetals
Nonmetals are found as gases, liquids (bromine only), and
solids. They are the most electronegative and are found in the
upper right-hand portion of the periodic table.
The lone
exception is hydrogen.
Section 21.2
Hydrogen
Hydrogen makes up about 70% of the mass of the universe. Even
though it makes up such a large percentage of the mass of the
universe, the mass of hydrogen gas is so small that it escapes the
gravitational pull of Earth and is not found in our atmosphere.
Compounds of hydrogen are known as hydrides. They are classified
as ionic hydrides (oxidation number of hydrogen is -1), covalent
hydrides which are covalent, and interstitial where the small
hydrogen atoms combine with transition metals resulting in a ratio
of hydrogen atoms to metal atoms that is a variable.
Hydrogen is the only element whose isotopes have unique names.
Hydrogen is 11H . Deuterium is 21H . Tritium is 31H . Because the
relative mass of these isotopes varies so significantly, the
chemistry of such compounds
as H2O and D2O are considerably
different. Your author points out that D2O is a toxic substance
and cannot replace normal water in our diet.
Hydrogenation is the addition of hydrogen to compounds with
double or triple bonds. This process is especially important in
controlling the poly-unsaturation of fats and oils used in
cooking.
Section 21.3
Carbon
Carbon compounds will be covered in much greater detail in
Chapter 24.
This section deals with inorganic compounds of
carbon. Your author points out that, in fact, "diamonds are not
forever" because thermodynamically
C(diamond) → C(graphite)
∆ G ° = - 2.87 kJ
and since ∆Go is negative this reaction is spontaneous; however,
this process is extremely slow.
An extremely dangerous reaction is the reaction of any metal
cyanide with acids. The reason is that hydrogen cyanide gas will
result. Hydrogen cyanide gas is extremely toxic and should be
avoided at all times.
Section 21.4
Perhaps
the
Nitrogen and Phosphorus
best
known
nitrogen-containing
compound
is
Liquid ammonia can autoionize to form NH +
4 and NH 2 .
It can be used as a solvent where the solutes will react with
water or where a more basic solvent is required.
Hydrazine,
methyl hydrazine and dinitrogen tetroxide are used as rocket
fuels.
We have covered various oxides of nitrogen when we
discussed pollutants found in the atmosphere in Chapter 17.
White phosphorus is found as P4 molecules. It can be converted
to red phosphorus, a polymeric form, at about 300oC. The reaction
of white phosphorous with hot concentrated sodium hydroxide
results in the formation of phosphine, PH3. Phosphine in turn can
This should not be
react with oxygen gas to form H3PO4(s).
confused with phosphoric acid that is prepared industrially by
reacting calcium phosphate with sulfuric acid.
ammonia.
Ca 3 (PO 4 )2 (s) + 3 H 2 SO4 (aq) → 2 H3 PO4 (aq) + 3 CaSO4 (s)
Section 21.5
Oxygen and Sulfur
Oxygen can be found as three types of oxides: oxide (oxidation
number of -2), peroxide (oxidation number of -1), and superoxide
(oxidation number of -1/2). Hydrogen peroxide, H2O2, is probably
the most common peroxide. Your students have probably encountered
this compound as a mild antiseptic. It also is used to bleach
hair to what has been known in the past as "bleached blondes".
We discussed ozone in Chapter 17 since it is a component of
the atmosphere (ozone layer) and is a pollutant. It is the second
strongest oxidizer only exceeded by F2. Because of this care must
be taken to keep ozone away from strong reducing agents. It is a
strong enough oxidizer to react with all common metals including
mercury.
Sulfur forms S8 molecules in its most stable form. If your
students have been near oil wells, they have probably smelled
hydrogen sulfide (odor of rotten eggs) since many oil wells
Hydrogen sulfide is also used in qualitative
produce H2S(g).
analysis to form the insoluble sulfides for Group II and Group III
cations. The most common method for producing hydrogen sulfide
for qualitative analysis is the hydrolysis of thioacetamide.
Sulfur forms several oxides including SO2 and SO3. The world’s
most important industrial chemical is sulfuric acid. Two other
important sulfur-containing compounds are CS2 (used as a
nonaqueous solvent) and SF6 which is an inert gas.
Section 21.6
The Halogens
Fluorine is the most reactive of all halogens. Common
fluorine-containing compounds include HF (a weak acid that is
highly reactive) and sodium fluoride (NaF). Fluorine gas reacts
with sodium hydroxide by the following reaction:
2 F2 (g) + 2 NaOH(aq) → 2 NaF(aq) + H 2 O(l) + OF2 (g)
The compound OF2 is unusual in that oxygen has a positive two
oxidation number. The only possible oxidation numbers for F are
Fluorine is used to produce
zero (F2) or -1 (compounds).
polytetrafluorothylene (Teflon), the non-stick compound that we
are all familiar with.
Chlorine, bromine, and iodine have similar reactions but are
considerably different from fluorine. They form the strong acids
HCℓ, HBr, and HI.
Chlorine gas is used as a disinfectant.
Bromine compounds include ethylene dibromide which is used as an
insecticide and a lead scavenger in gasoline. Iodine is unusual
in that it sublimes to form a violet gas directly from its
crystalline form.
This can be demonstrated by placing a few
crystals of iodine in a stoppered test tube and immersing the
tube in a beaker of hot water. The crystals will sublime and
reform on the walls of the tube in the cooler region.