Gián án Chapter 22 Chemistry of the Nonmetals

Chapter 22
Chemistry
of the
Nonmetals
2011, NKMB Co., Ltd.
Chemistry, Julia Burdge, 2
st
Ed.
McGraw Hill.
Mr. Truong Minh Chien ;
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2
Nanotubes
•
nanotubes – long, thin, hollow cylinders of atoms
•
carbon nanotube = sp
2
C in fused hexagonal rings

electrical conductors
•
boron-nitride nanotubes = rings of alternating B and N
atoms

isoelectronic with C

similar size to C

average electronegativity of B & N about the same as C


electrical insulators
Chemistry, Julia Burdge, 2
nd
e., McGraw Hill.
3
Insulated Nanowire
Chemistry, Julia Burdge, 2
nd
e., McGraw Hill.
4
Properties of BN and C
Chemistry, Julia Burdge, 2
nd
e., McGraw Hill.
5
Main Group Nonmetals
Chemistry, Julia Burdge, 2
nd
e., McGraw Hill.
6
Atomic Radius and Bonding
•
atomic radius decreases across the period
•
electronegativity, ionization energy increase across the
period
•
nonmetals on right of p block form anions in ionic
compounds


often reduced in chemical reactions

making them oxidizing agents
•
nonmetals on left of p block can form cations and
electron-deficient species in covalent bonding
•
nonmetals near the center of the p block tend to use
covalent bonding to complete their octets
•
bonding tendency changes across the period for
nonmetals from cation and covalent; to just covalent; to
anion and covalent
Chemistry, Julia Burdge, 2
nd
e., McGraw Hill.
7
Silicates
•
the most abundant elements of the Earth’s crust
are O and Si
•
silicates are covalent atomic solids of Si and O

and minor amounts of other elements

found in rocks, soils, and clays

silicates have variable structures – leading to the
variety of properties found in rocks, clays, and soils

Chemistry, Julia Burdge, 2
nd
e., McGraw Hill.
8
Bonding in Silicates
•
each Si forms a single covalent bond to 4 O

sp
3
hybridization

tetrahedral shape

Si-O bond length is too long to form Si=O
•
to complete its octet, each O forms a single
covalent bond to another Si
•
the result is a covalent network solid
Chemistry, Julia Burdge, 2
nd
e., McGraw Hill.
9
Quartz
•
a 3-dimensional covalent network
of SiO
4
tetrahedrons

•
generally called silica
•
formula unit is SiO
2
•
when heated above 1500°C and
cooled quickly, get amorphous
silica which we call glass
Chemistry, Julia Burdge, 2
nd
e., McGraw Hill.
10
Aluminosilicates
•
Al substitutes for Si in some of the lattice sites
•
SiO
2
becomes AlO
2
−
•
the negative charge is countered by the inclusion
of a cation

Albite = ¼ of Si replaced by Al; Na(AlO
2
)(SiO
2

)
3

Anorthite = ½ of Si replaced by Al; Ca(AlO
2
)
2
(SiO
2
)
2
Chemistry, Julia Burdge, 2
nd
e., McGraw Hill.
11
Silicates Made of Individual Units
•
O of SiO
4
picks up electrons from metal to form SiO
4
4−
•
if the SiO
4
4−
are individual units neutralized by cations, it
forms an orthosilicate

willemite = Zn

2
SiO
4
•
when two SiO
4
units share an O, they form structures
called pyrosilicates with the anion formula Si
2
O
7
6−

hardystonite =Ca
2
ZnSi
2
O
7
Chemistry, Julia Burdge, 2
nd
e., McGraw Hill.
12
Single Chain Silicates
•
if the SiO
4
4−
units link as long
chains with shared O, the

structure is called a pyroxene
•
formula unit SiO
3
2-
•
chains held together by ionic
bonding to metal cations
between the chains

diopside = CaMg(SiO
3
)
2
where Ca
and Mg occupy lattice points
between the chains
Chemistry, Julia Burdge, 2
nd
e., McGraw Hill.
13
Double Chain Silicates
•
some silicates have 2
chains bonded together
at ½ the tetrahedra –
these are called
amphiboles
•
often results in fibrous

minerals

asbestos

tremolite asbestos =
Ca
2
(OH)
2
Mg
5
(Si
4
O
11
)
2
Chemistry, Julia Burdge, 2
nd
e., McGraw Hill.
14
Sheet Silicates
•
when 3 O of each
tetrahedron are shared,
the result is a sheet
structure called a
phyllosilicate
•
formula unit = Si

2
O
5
2−
•
sheets are ionically
bonded to metal cations
that lie between the
sheets
•
talc and mica
Chemistry, Julia Burdge, 2
nd
e., McGraw Hill.
Tro, Chemistry: A Molecular Approach 15
Mica: a Phyllosilicate
Tro, Chemistry: A Molecular Approach 16
Silicate Structures
Tro, Chemistry: A Molecular Approach 17
Boron
•
metalloid
•
at least 5 allotropes, whose structures are
icosahedrons

each allotrope connects the icosahedra in
different ways
• less than 0.001% in Earth’s crust, but
found concentrated in certain areas


almost always found in compounds with O

borax = Na
2
[B
4
O
5
(OH)
4
]⋅8H
2
O

kernite = Na
2
[B
4
O
5
(OH)
4
]⋅3H
2
O

colemanite = Ca
2
B

6
O
11
⋅5H
2
O
•
used in glass manufacturing – borosilicate
glass = Pyrex
•
used in control rods of nuclear reactors
Tro, Chemistry: A Molecular Approach 18
Boron Trihalides
•
BX
3
•
sp
2
B

trigonal planar, 120° bond angles

forms single bonds that are shorter and stronger than
sp
3
C

some overlap of empty p on B with full p on halogen
•

strong Lewis Acids
Tro, Chemistry: A Molecular Approach 19
Boron-Oxygen Compounds
•
form structures with trigonal
BO
3
units
•
in B
2
O
3
, six units are linked
in a flat hexagonal B
6
O
6
ring

melts at 450°C

melt dissolves many metal
oxides and silicon oxides to form
glasses of different compositions
Tro, Chemistry: A Molecular Approach 20
Boranes
closo-Boranes
•
compounds of B and H

•
used as reagent in hydrogenation of C=C
•
closo-Boranes have formula B
n
H
n
2−
and form
closed polyhedra with a BH unit at each vertex
Tro, Chemistry: A Molecular Approach 21
Boranes
nido-Boranes and arachno-Boranes
•
nido-Boranes have formula B
n
H
n+4
consisting of
cage B missing one corner
•
arachno-Boranes have formula B
n
H
n+6
consisting
of cage B missing two or three corners
Tro, Chemistry: A Molecular Approach 22
Carbon
•

exhibits the most versatile bonding of all the
elements
•
diamond structure consists of tetrahedral sp
3

carbons in a 3-dimensional array
•
graphite structures consist of trigonal planar sp
2

carbons in a 2-dimensional array

sheets attracted by weak dispersion forces
•
fullerenes consist of 5 and 6 member carbon
rings fused into icosahedral spheres of at least
60 C
23
Crystalline Allotropes of Carbon
Diamond Graphite Buckminster-
fullerene, C
60
Color clear-blue black black
Density, g/cm
3
3.53 2.25 1.65
Hardness, Mohs Scale 10 0.5
Electrical Conductivity, (µΩ•cm)
-1

~10
-11
7.3 x 10
-4
~10
-14
Thermal Conductivity, W/cm•K 23
20 ()
Melting Point, °C
~3700 ~3800 800 sublimes
Heat of Formation (kcal/mol) 0.4 0.0 9.08
Refractive Index 2.42 ─ 2.2 (600 nm)
Source Kimberlite
(S. Africa)
Pegmatite
(Sri Lanka)
Shungite
(Russia)
Tro, Chemistry: A Molecular Approach 24
Allotropes of Carbon - Diamond
Inert to Common Acids
Inert to Common Bases
Negative Electron Affinity
Transparent
Hardest
Best Thermal Conductor
Least Compressible
Stiffest
Tro, Chemistry: A Molecular Approach 25
Allotropes of Carbon - Graphite

Soft and Greasy Feeling
Solid Lubricant
Pencil “Lead”
Conducts Electricity
Reacts with Acids and
Oxidizing Agents