John E. McMurry • Robert C. Fay
General Chemistry: Atoms First
Chapter 19
The Main-Group Elements
Lecture Notes
Alan D. Earhart
Southeast Community College • Lincoln, NE
Copyright © 2010 Pearson Prentice Hall, Inc.
Chapter 19/2
A Review of General Properties
and Periodic Trends
A Review of General Properties and Periodic Trends
A Review of General Properties
and Periodic Trends
Distinctive Properties of the SecondRow Elements
Distinctive Properties of the
Second-Row Elements
•
Their small size and high electronegativity accentuate
their nonmetallic behavior.
•
Hydrogen bonding (typically N, O, and F).
•
Out of HF, HCl, HBr, and HI, HF is the only weak
hydrohalic acid.
Chapter 19/7
Distinctive Properties of the
Second-Row Elements
•
They generally form a maximum of four covalent bonds.
Group 5a
Row 2
Row 3
Chapter 19/8
Distinctive Properties of the
Second-Row Elements
•
C, N, and O form multiple bonds by pi overlap of their 2p
orbitals.
Distinctive Properties of the
Second-Row Elements
•
C, N, and O form multiple bonds by pi overlap of their 2p
orbitals.
Chapter 19/10
The Group 3A Elements
The Group 3A Elements
•
•
Valence electron configuration is ns2np1.
Primary oxidation state is +3. The heavier ones also
exhibit a +1 state.
Boron
B2O3(l) + 3Mg(s)
Heat
2B(s) + 3MgO(s)
1200 °C
2BBr3(g) + 3H2(g)
2B(s) + 6HBr(g)
Ta wire
•
Strong and hard substance.
•
High-melting point (2075 °C).
•
Chemically inert at room temperature except with
fluorine.
Chapter 19/13
Boron
Boron halides are highly reactive, volatile, covalent compounds.
Chapter 19/14
Boron
•
Boron hydrides, or boranes, are volatile, molecular
compounds with formulas BnHm.
Chapter 19/15
Boron
• Boron hydrides, or boranes, are
volatile, molecular compounds with
formulas BnHm.
•
Diborane is electron-deficient.
The bridging H atom is bonded
to both B atoms and forms a
three-center, two-electron bond
(3c-2e bond).
Aluminum
2Al(s) + 3X2(g, l, or s)
4Al(s) + 3O2(g)
2Al(s) + N2(g)
2AlX3(s)
X = F, Cl, Br, or I
2Al2O3(s)
2AlN(s)
Chapter 19/17
Aluminum
Chapter 19/18
Aluminum
Acidic solution:
2Al(s) + 6H1+(aq)
2Al3+(aq) + 3H2(g)
Basic solution:
2Al(s) + 2OH1-(aq) + 6H2O(l)
2Al(OH)41-(aq) + 3H2(g)
Chapter 19/19
The Group 4A Elements
The Group 4A Elements
•
•
Valence electron configuration is ns2np2.
The group 4a elements exemplify the increase in metallic
character down a group in the periodic table.
Chapter 19/21
Carbon
•
Second most abundant element in living organisms.
•
Multiple allotropes (diamond, graphite, fullerene, and
nanotubes).
•
Present in carbonate minerals and fossil fuels.
Chapter 19/22
Carbon
Chapter 19/23
Carbon
Oxides of Carbon
2C(s) + O2(g)
•
∆H° = -221 kJ
In excess oxygen, CO is oxidized to CO2:
2CO(s) + O2(g)
•
2CO(g)
2CO2(g)
∆H° = -566 kJ
The production of methanol is one of the main industrial
uses of CO:
250 °C
CO(g) + 2H2(g)
Cu/ZnO/Al2O3 catalyst
CH3OH(g)
Chapter 19/24
Carbon
Oxides of Carbon
Oxyhemoglobin
Hb-O2 + CO
Hb-CO + O2
Carboxyhemoglobin
Chapter 19/25
Carbon
CO2 Production
CH4(g) + O2(g)
•
CO2(g) + 2H2O(g)
Industrially, CO2 is produced by the yeast-catalyzed
fermentation of sugar in the manufacture of alcoholic
drinks:
Yeast
C6H12O6(aq)
glucose
2CH3CH2OH(aq) + 2CO2(g)
ethanol
Chapter 19/26
Carbon
CO2 Production
Heat
CaCO3(s)
Na2CO3(s) + 2H1+(aq)
CaO(s) + CO2(g)
2Na1+(aq) + CO2(g) + H2O(l)
Chapter 19/27
Carbon***
Carbonates
CO2(aq) + H2O(l)
•
H2CO3(aq)
Washing soda, Na2CO3•10H2O, is used to launder
textiles:
Ca2+(aq) + CO32-(aq)
CO32-(aq) + H2O(l)
•
H1+(aq) + HCO31-(aq)
CaCO3(s)
HCO31-(aq) + OH1-(aq)
Baking soda, NaHCO3, reacts with acids to yield CO2:
NaHCO3(aq) + H1+(aq)
Na1+(aq) + CO2(g) + H2O(l)
Chapter 19/28
Carbon
Hydrogen Cyanide and Cyanides
•
HCN is very toxic and is produced when metal cyanides
are acidified:
CN1-(aq) + H1+(aq)
•
HCN(aq)
Cyanide is a pseudohalide ion because it behaves like
chloride ion:
4Au(aq) + 8CN1-(aq) + O2(g) + 2H2O(l)
4Au(CN)21-(aq) + 4OH1-(aq)
2Au(CN)21-(aq) + Zn(s)
2Au(s) + Zn(CN)42-(aq)
Chapter 19/29
Carbon
Carbides
•
A binary inorganic compound in which carbon has a
negative oxidation state:
2200 °C
CaO(s) + 3C(s)
•
CaC2(s) + CO(g)
Calcium carbide is used to prepare acetylene, C2H2, for
oxyacetylene welding:
CaC2(s) + 2H2O(l)
C2H2(g) + Ca(OH)2(s)
Chapter 19/30
Silicon
•
Silica (SiO2, sand) is reacted with coke in an electric
furnace:
Heat
SiO2(l) + 2C(s)
Si(l) + 2CO(g)
•
Hard, gray semiconducting solid.
•
Melts at 1414 °C.
Chapter 19/31
Silicon
•
To purify the silicon for ultrapure applications
(semiconductors):
Si(s) + 2Cl2(g)
SiCl4(l)
Heat
SiCl4(g) + 2H2(g)
•
Si(s) + 4HCl(g)
Purified further by a process called zone refining.
Chapter 19/32
Silicon
Chapter 19/33
Silicon
Silicates
Chapter 19/34
Silicon
Silicates
Silicon
Silicates
Silicon
Silicates
Silicon
Chapter 19/38
Germanium, Tin, and Lead
Germanium, Tin, and Lead
•
Germanium is a relatively high-melting, brittle
semiconductor with the same crystal structure as
diamond and silicon.
•
Tin has two allotropic forms:
•
•
•
A brittle, semiconducting form with a diamond
structure called gray tin.
A silvery, low-melting, white metallic form called
white tin.
Lead is a soft, low-melting metal.
Chapter 19/40
Germanium, Tin, and Lead
Germanium, Tin, and Lead
•
Tin is obtained from the mineral cassiterite (SnO2):
Heat
SnO2(s) + 2C(s)
•
Sn(l) + 2CO(g)
Lead is obtained from the ore galena (PbS):
2PbS(s) + 3O2(g)
PbO(s) + CO(g)
2PbO(s) + 2SO2(g)
Pb(l) + CO2(g)
Chapter 19/42
Germanium, Tin, and Lead
Chapter 19/43
The Group 5A Elements
The Group 5A Elements
•
Valence electron configuration is ns2np3.
•
N and P are typical nonmetals, As and Sb are
semimetals, and Bi is a metal.
The Group 5A Elements
Nitrogen
•
Elemental nitrogen is a colorless, odorless, tasteless gas
that makes up 78% of the Earth’s atmosphere by volume.
•
It is the most volatile component of liquid air (bp -196 °C)
and is easily separated from the less volatile oxygen (bp
-183 °C) and argon (bp -186 °C) by fractional distillation.
•
Nitrogen will react with hydrogen to form ammonia, but
requires high pressures, high temperatures, and a
catalyst (Haber process):
400-500 °C, 130-300 atm
N2(g) + 3H2(g)
Fe/K2O/Al2O3 catalyst
2NH3(g)
Chapter 19/47
Nitrogen
Nitrogen
Ammonia
•
Ammonia is a starting compound for the synthesis of
many important nitrogen compounds.
•
It is very soluble in water.
•
Neutralization of aqueous ammonia with acids yields
ammonium salts, which resemble alkali metal salts in
their solubility.
•
It is a Brønsted-Lowry base:
NH3(aq) + H2O(l)
NH41+(aq) + OH1-(aq)
Chapter 19/49
Nitrogen
Hydrazine
•
Hydrazine can be prepared by the reaction of ammonia
with a basic solution of sodium hypochlorite (NaOCl):
2NH3(aq) + OCl1-(aq)
N2H4(aq) + H2O(l) + Cl1-(aq)
•
Pure hydrazine is a poisonous, colorless liquid that smells
like ammonia, freezes at 2°C, and boils at 114 °C.
•
It is violently explosive in the presence of air or other
oxidizing agents:
2N2H4(l) + N2O4(l)
3N2(g) + 4H2O(g) ∆H° = -1049 kJ
Chapter 19/50
Nitrogen
Oxides of Nitrogen
•
Nitrous oxide (N2O) is a colorless, sweet-smelling gas
obtained when molten ammonium nitrate is heated gently
at about 270 °C:
Heat
NH4NO3(l)
•
N2O(g) + 2H2O(g)
Nitric oxide (NO) is a colorless gas, produced in the
laboratory when copper metal is treated with dilute nitric
acid:
3Cu(s) + 2NO31-(l) + 8H1+(aq)
3Cu2+(aq) + 2NO(g) + 4H2O(l)
Chapter 19/51
Nitrogen
Oxides of Nitrogen
•
Nitrogen dioxide (NO2) is a highly toxic, reddish-brown
gas that forms rapidly when nitric oxide is exposed to air:
2NO(g) + O2(g)
•
NO2 can also be produced when copper reacts with
concentrated nitric acid:
Cu(s) + 2NO31-(l) + 4H1+(aq)
•
2NO2(g)
Cu2+(aq) + 2NO2(g) + 2H2O(l)
Nitrogen dioxide tends to dimerize:
2NO2(g)
N2O4(g)
∆H° = -55.3 kJ
Chapter 19/52
Nitrogen
Nitrogen
Oxides of Nitrogen
•
Nitrous acid (HNO2) is formed by a reaction between
nitrogen dioxide and water:
2NO2(g) + H2O(l)
HNO2(aq) + H1+(aq) + NO31-(aq)
Chapter 19/54
Nitrogen
Oxides of Nitrogen
•
Nitric acid (HNO3) is produced industrially by the
multistep Ostwald process:
850 °C
4NH3(g) + 5O2(g)
Pt/Rh catalyst
2NO(g) + O2(g)
3NO2(g) + H2O(l)
4NO(g) + 6H2O(g)
2NO2(g)
2HNO3(aq) + NO(g)
Chapter 19/55
Nitrogen
Oxides of Nitrogen
•
Concentrated nitric acid often has a yellow-brown color
due to the presence of a small amount of NO2:
4HNO3(aq)
4NO2(aq) + O2(g) + 2H2O(l)
Chapter 19/56
Nitrogen
Oxides of Nitrogen
•
Aqua regia is a mixture of concentrated HCl and
concentrated HNO3 in a 3:1 volume ratio which will
oxidize even inactive metals like gold:
Au(s) + 3NO31-(aq) + 6H1+(aq) + 4Cl1-(aq)
AuCl41-(aq) + 3NO2(g) + 3H2O(l)
Chapter 19/57
Phosphorus
•
Phosphorus is the most abundant element of group 5a. It
is obtained by reacting phosphate rock, coke, and silica
sand in an electric furnace:
1500 °C
2Ca3(PO4)2(s) + 10C(s) + 6SiO2(s)
P4(g) + 10CO(g) + 6CaSiO3(l)
Chapter 19/58
Phosphorus
•
The element exists in two allotropes: white phosphorus
and red phosphorus:
Phosphorus
•
White phosphorus:
•
•
•
•
Toxic and waxy, white solid.
Low melting point (44 °C).
Soluble in nonpolar solvents.
Highly reactive in air and must be stored under water.
Phosphorus
•
White phosphorus:
•
•
•
•
•
Toxic and waxy, white solid.
Low melting point (44 °C).
Soluble in nonpolar solvents.
Highly reactive in air and must be stored under water.
Red phosphorus:
•
•
•
•
Nontoxic with a polymeric structure.
High melting point (579 °C).
Less soluble than white phosphorus.
It does not ignite on contact with air (less reactive).
Chapter 19/61
Phosphorus
•
Phosphine (PH3) is a colorless, extremely poisonous
gas. Unlike ammonia, NH3, its aqueous solutions are
neutral. It will burn in air and oxidize to form phosphoric
acid:
PH3(g) + 2O2(g)
•
H3PO4(l)
Phosphorus halides (PX3 or PX5, X = F, Cl, Br, or I) are
formed by reacting the element with halides:
Limited amount of X2:
P4 + 6X2
4PX3
Excess amount of X2: P4 + 10X2
4PX5
Chapter 19/62
Phosphorus
Chapter 19/63
Phosphorus
•
Oxides and oxoacids are formed when the element is
burned in air or oxygen:
Limited amount of O2: P4(s) + 3O2(g)
P4O6(s)
Excess amount of O2: P4(s) + 5O2(g)
P4O10(s)
Phosphorus
Chapter 19/65
The Group 6A Elements
The Group 6A Elements
•
Valence electron configuration is ns2np4.
•
A common oxidation state is -2. The stability of this state
decreases with increasing metallic character.
•
Oxygen is a good oxidizing agent but H2Se and H2Te are
good reducing agents.
Chapter 19/67
The Group 6A Elements
The Group 6A Elements
Selenium
Tellurium
Chapter 19/69
Sulfur
•
Sulfur is one of the 10 most abundant elements in the
human body.
•
It is the sixteenth most abundant element in the Earth’s
crust and is present in minerals such as pyrite (FeS2),
galena (PbS), cinnabar (HgS), and gypsum
(CaSO4•2H2O).
•
It is also present in natural gas as H2S and crude oil as
organic sulfur compounds.
Chapter 19/70
Sulfur
Chapter 19/71
Sulfur
•
Elemental sulfur is obtained by recovery from natural gas
and crude oil:
2H2S(g) + 3O2(g)
2SO2(g) + 2H2O(g)
300 °C
SO2(g) + 2H2S(g)
Fe2O3 catalyst
3S(g) + 2H2O(g)
Chapter 19/72
Sulfur
Chapter 19/73
Sulfur
Chapter 19/74
Sulfur
Hydrogen Sulfide
•
It is a colorless gas (bp -60 °C) and has a strong odor
associated with rotten eggs.
•
It is extremely toxic and can cause death at 100 ppm.
•
For qualitative analysis in the laboratory, the gas is
usually generated in solution by the hydrolysis of
thioacetamide:
Sulfur
Oxides and Oxoacids of Sulfur
•
Sulfur dioxide (SO2) is formed when sulfur burns in air:
S(s) + O2(g)
•
SO2(g)
Sulfuric acid (H2SO4) is manufactured industrially by the
contact process:
S(s) + O2(g)
SO2(g)
Heat
2SO2(g) + O2(g)
V2O5 catalyst
SO3(g) + H2O (in conc. H2SO4)
2SO3(g)
H2SO4 (in conc. H2SO4)
Chapter 19/76
Sulfur
Uses of Sulfuric Acid
The Halogens: Oxoacids and
Oxoacid Salts
The Halogens: Oxoacids and
Oxoacid Salts
•
Halogens have a valence electron configuration of
ns2np5.
•
Acid strength increases with the oxidation state of the
halogen.
Chapter 19/79
The Halogens: Oxoacids and
Oxoacid Salts
•
A hypohalous acid is formed when Cl2, Br2, or I2
dissolves in cold water:
X2(g, l, or s) + H2O(l)
•
HOX(aq) + H1+(aq) + X1-(aq)
Bleach (aqueous NaOCl), for example, can be made by
dissolving chlorine in a basic solution of sodium
hydroxide (NaOH):
Cl2(g, l, or s) + 2OH1-(aq)
OCl1-(aq) + Cl1-(aq) + H2O(l)
Chapter 19/80
The Halogens: Oxoacids and
Oxoacid Salts
•
Chlorate salts are formed when chlorine, for example,
reacts with hot aqueous NaOH:
3Cl2(g) + 6OH1-(aq)
•
ClO31-(aq) + 5Cl1-(aq) + 3H2O(l)
Perchloric acid is produced by reacting sodium
perchlorate (NaClO4) with concentrated HCl:
Electrolysis
ClO31-(aq) + H2O(l)
NaClO4(s) + HCl(aq)
ClO41-(aq) + H2(g)
HClO4(aq) + NaCl(s)
Chapter 19/81
The Halogens: Oxoacids and
Oxoacid Salts
•
Iodine differs from the other halogens because it will form
more than one perhalic acid:
100 °C
H5IO6(s)
12 mm Hg
HIO4(s)+ 2H2O(g)
Chapter 19/82