Introduction to Chemistry – Background for Nanoscience and Nanotechnology
Prof. Petr Vanýsek
Part I
Introduction to Chemistry Principles
Introduction to measurements
In the world of science, just like in everyday life, measurements of
quantities are the way of life and an important method of understanding world.
For example, when pumping gasoline, two measures come in play. One is the
volume of gasoline, usually measured in gallons; the other is the counting
measure of money, the amount of dollars and cents, which we have to pay for
the purchase. The relationship between the two, the price, dollars/gallon, is a
simple algebraic relationship, which makes the world run. Considering the cost of
gasoline and the work needed to earn money, it should be obvious why neither
gasoline volume, not money in the bank account, are only estimated. Rather,
they are measured and guarded with vigilance.
Introduction to measurements
The following are some simple example of measurements of distance of
size. Keep in mind, they we measure both extreme distances (astronomy) and
small distances (size of an atom).
Dynamics of the scale – from the wavelength of x-rays to
astronomic distances.
Focus on the “middle” scale size from visible objects – person, hand
(where did inch come from?), fingernail thickness, hair diameter, mite, microbe,
virus, finally atom and a molecule.
Relevant dimensions:
kilometers (1000 meter or 10+3 m)
meters
centimeters (ca. 2-1/2 cm = 1 inch)
millimeter
nanometers
Angstroms (10-10 m) – size of an atom
Units of measurement
Civilian – In the 80’s there was push to align the US measures with the
rest of the world, but this effort largely failed and we are saddled with fairly
convenient units, which the rest of the world does not understand. The rest of the
world, for the most part, accepted metric system, which, with proper definitions, is
the basis of the scientific system of measures.
SI Units (SI – System international).
This system consists of seven base (fundamental) units, and derived
units.
Some of the units can be either too large or too small to use comfortably,
because we usually like to deal with small whole numbers. For example, the
distance from DeKalb to Chicago is about 65 miles, which would be in SI units of
distance 104000 meters. The three zeros for the magnitude are cumbersome
and hard to read. Thus a multiple of one thousand meters, the kilometer, is
introduced and the distance is more readable 104 km. The method of using these
multiples relies on using prefixed before the unit, as in our case, where k stands
for kilo (i.e., thousand) and the base unit m (meter). Similarly, a prefix for
smaller numbers can be used. One thousandth of a meter becomes a millimeter
(mm).
Note also, that in measurements we should look at the number of
significant figures to be used. The “65 miles to Chicago” is clearly approximation.
Are we going to the Loop? And exactly from where in DeKalb did we start and
which way are we going. So the metric equivalent from DeKalb to Chicago
should be “about 100 km.”
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The following table shows most of the prefixes.
Note the SI unit for length is the meter (m) whereas the SI unit for mass is
the kilogram (kg). 1 kg weighs 2.2046 lb.
Standard units of distance measurement
Standard units:
length
Meter (a little more than 3 feet)
too large for some purpose
millimeter, centimeter
(multiples of 10, e.g., 1 meter = 1000 cm)
Inch – nonstandard unit, thumb (sp. thumb=pulgar, inch=pulgada, Greek
inch=daktulos=finger)
Temperature
There are three temperature scales:
Kelvin scale, used in science. It has the same temperature increment as the
Celsius scale, but a different starting point. The lowest temperature possible
(absolute zero) is zero Kelvin, also called absolute zero: 0 K = -273.15 oC.
The Celsius scale is fairly common, with the point of freezing water set at 0 and
the point of boiling water at 100. The Fahrenheit, these days mostly used only in
the US, does not convert quite easily into Celsius, both addition and
multiplication has to be used.
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Why dimensions matter?
Nanomaterials – particles of nanometer size
Nano-scale materials often have very different
properties from bulk materials
e.g. color and reactivity
• 3nm iron particle has 50% of atoms on the surface
• 10nm particle has 20% of atoms on the surface
• 30nm particle has 5% of atoms on the surface
With scaling down, many properties change. One can illustrate it on
example of bread making. Good bread will have crust which will be distinct from
the inside core. Of the loaf is made smaller and smaller, the inside will become
more like the crust. Conversely, with a huge loaf, the crust might be just fine, but
the inside would simply stay raw.
Clearly, when one concentrate on parts of human body, smaller and
smaller compartments can be studied, and from appendages, to organelles,
molecules and atoms one gets to the smaller and smaller, and eventually, the
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smallest components. Making the trip from the “normal” to small, we are entering
the “nanoworld.” The word nano comes from the prefix nano (10-9) combined
with length unit a meter. Thus the “nanoworld” will have dimensions expressed in
nanometers, usually form 1 nm to 100 nm.
The world in the nanoscale, as small as it is, is incredibly varied, unusual, and
incredibly useful.
The scale of things
Units of volume
The units for volume are given by (units of length)3.
SI unit for volume is 1 m3.
We usually use 1 mL = 1 cm3.
Other volume units:
1 L = 1 dm3 = 1000 cm3 = 1000 mL
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Concentration
Amount per volume
grams per liter
moles per liter.
What is the mole? -- Amount of material.
mass – in kilograms or grams,
there is also possibility to count particles (atoms or molecules)
counting large numbers – special designation for certain multiples
12 = dozen
500 = ream
6.022 x 1023 = mole
One mole is not peculiar number. It was picked because one mole of
atoms has exactly the weight of the atomic number given in grams -- a very
handy measure.
Temperature:
Vigor of movement of paticles – atoms or molecules.
Scientific units – Degrees Celsius (water freezes at zero and boils at hundred).
Kelvin – same spacing as Celsius, starts at absolute zero and 0 oC is 273.15 K.
Temperature can be measured based on change of physical property – change
of volume with temperature.
Thermal expansion – volumetric thermal expansion.
For many years the classical volume expansion device was the mercury
thermometer.
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Conversion of temperature units
Some units need to be converted, e.g., centimeters to inches, which is simple
multiplication.
Lcm = 2.54*Lin
Temperature conversion Fahrenheit to Celsius is a bit more involved
Tc = (5/9)*(Tf-32)
Tf = ((9/5)*Tc)+32
Learning from large dimensions, applying in nanoworld.
The above example, taken from a general chemistry textbook, shows how
the principle of expansion of mercury on large scale, in a glass tube of a
thermometer, was applied to a device constructed from special small channels.
Gallium, instead of mercury, was used as the expanding liquid.
Large dynamic range of dimensions.
The following diagram shows the scale of wavelengths, an intangible, but
very relevant property. It is related to dimensions of physical objects, from
skyscrapers, down to the size of the nucleus of an atom. The nanoworld appears
between the size of an atom and a virus in this figure.
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Material can have different forms. One remarkable example is the two crystalline
forms of the element carbon, existing either as the more common graphite, or the
rare, but desirable, diamond. Diamond has many useful properties and therefore
its synthesis is desirable process. Advances in nanochemistry make this
possible.
Another form of carbon, discovered fairly recently, are nanosize structures, such
as nanospheres and nanotubes, consisting of arranged atoms of carbon. The
spheres are known and fullerenes and an example is shown in the following
pictures.
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Acceptance of nanotechnology
Once the research moves from the confines of a few laboratories and becomes
potentially viable commercial venture, the public acceptance becomes important
for its viability along any scientific, social or economic benefits. There is lot of
unknown in nanoscience and given past experience with outcomes of new
discoveries, people tend to be skeptical, not trusting, or outright hostile towards
novel ideas. The following graph shows acceptance of nanotechnology, plotted
against predominance of faith in different nations.
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Technology implements scientific discoveries in practical and scaled-up
ways. The scientific discoveries usually happen outside technology process,
such as in physics, chemistry or biology. Of course, there are numerous
exceptions to this observation and plenty of discoveries can be assigned to
technology alone. However, to understand nanotechnology, one has to
understand the science that underpins all and chemistry is one of the supporting
pillars of scientific knowledge.
Why study chemistry?
It is the study of the properties of materials and the changes that materials
undergo.
It is central to our understanding of other sciences.
It is substantial part of nanoscience and nanotechnology.
The study of chemistry uses molecular perspective and is based on the following:
Matter is the physical material of the universe
Matter is made of relatively few elements
On the microscopic level, matter consists of atoms and molecules
Molecules (as we will see) may consist of the same type of atoms or
different types of atoms.
The properties of the molecules depend on the type of atoms, but also on
the arrangement of the atoms in the molecule.
The following figure shows several models of molecule, filling space.
Matter can exist in three different states, a gas, a liquid and a solid.
Classification of matter
The composition of the matter in the three states is the same, the physical
behavior is different.
Gases take the shape and the volume of their container. Gases can be
compressed to form liquids.
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Liquids take the shape of their container, but they do have their own
volume, independent on the container.
Solids are rigid and have a definite shape and volume.
Pure substances vs. Mixtures
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Elements consist of a unique type of atom.
Molecules can consist of more than one type of element.
Molecules that have only one type of atom (an element).
Molecules that have more than one type of atom (a compound).
If more than one atom, element, or compound are found together, then the
substance is a mixture.
If matter is not uniform throughout, then it is a heterogeneous mixture.
If matter is uniform throughout, it is homogeneous.
If homogeneous matter can be separated by physical means, then the
matter is a mixture.
If homogeneous matter cannot be separated by physical means, then the
matter is a pure substance.
If a pure substance can be decomposed into something else, then the
substance is a compound.
Examples of pure substances and a mixture on the atomic size perspective.
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Elements
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If a pure substance cannot be decomposed into something else, then the
substance is an element.
There are 114 elements known.
Each element is given a unique chemical symbol (one or two letters).
Elements are building blocks of matter.
The earth’s crust consists of 5 main elements.
The human body consists mostly of 3 main elements.
The abundance is shown in the next figure.
The language of chemistry – naming elements:
Classification of Matter
• Elements
• Chemical symbols with one letter have
that letter capitalized (e.g., H, B, C, N,
etc.)
• Chemical symbols with two letters have
only the first letter capitalized (e.g., He,
Be).
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Further classification of matter:
Classification of Matter
• Compounds
• If water is decomposed, then there will always be twice
as much hydrogen gas formed as oxygen gas.
• Pure substances that cannot be decomposed are
elements.
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•
•
•
Mixtures
Heterogeneous mixtures are not uniform throughout.
Homogeneous mixtures are uniform throughout.
Homogeneous mixtures are called solutions.
The properties of matter can be described as either physical or as chemical:
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Physical properties can be measure without changing the basic identity of
the substance (e.g., color, density, odor, melting point)
Chemical properties describe how substances react or change to form
different substances (e.g., hydrogen burns in oxygen)
Intensive physical properties do not depend on how much of the
substance is present.
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Examples: density, temperature, and melting point.
Extensive physical properties depend on the amount of substance
present.
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Examples: mass, volume, pressure.
To understand the distinction between pure substances and mixtures, one can
use the following flow chart:
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Substance can undergo either a physical change – change form one state to
another, or a chemical change, change form one composition to another.
Following diagram, burning of hydrogen in oxygen is an example of a chemical
change.
Properties of Matter
Physical and Chemical Changes
• When a substance undergoes a physical change, its
physical appearance changes.
– Ice melts: a solid is converted into a liquid.
• Physical changes do not result in a change of
composition.
• When a substance changes its composition, it undergoes a
chemical change:
– When pure hydrogen and pure oxygen react completely, they
form pure water. In the flask containing water, there is no
oxygen or hydrogen left over.
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Some of chemistry knowledge is already assumed. Here is the review of some of
the concepts.
Review of Chemistry
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•
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States of Matter
Atoms, Molecules and Ions
Subatomic particles
Periodic Table
Covalent and ionic bonding
Chemical reactions
Inter-molecular forces
States of Matter
Solid
Keeps shape
Keeps
volume
Salt, gold,
copper
Liquid
Takes shape
of container
Keeps
volume
Water,
alcohol, oil
Gas
Takes shape
of container
Takes volume Air, argon,
of container
helium,
methane
Plasma – like
a gas of
charged
particles.
Takes shape
of container
Takes volume Stars, nebula,
of container
lightning,
plasma
reactors
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Matter
• Solution: A uniform mixture of two substances
such that molecules are separate from each
other and move around randomly. Usually these
are liquids. Solutions are usually transparent.
• Colloids: A mixture of much larger particles
ranging from 20 nm to 100 μm. Milk and paint
are colloids.
• Grains: Some materials are made up of many
small crystals called grains. A grain is an
individual crystal of such a solid. Different grains
may have the crystal lattice oriented in different
directions.
Examples of grains in steel are shown in this micrograph, obtained by first
polishing the surface of a steel sample and than slightly etching the surface with
an acid. The different faces of the grains dissolve at different rates, making
etching very useful in visualizing inhomogeneities.
Grain Structure in Steel
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Review of elements, atoms and molecules:
Elements, Atoms and Molecules
• Atoms: All matter is made up of tiny particles called atoms.
• Molecules: Sometimes two or more atoms are found bound together
to form molecules.
• The atoms can be categorized into about 115 different types based
on the charge of the nucleus.
• Elements are made up of only one type of atom.
• The element carbon takes the form of graphite, diamond and
buckminsterfullerene as well as others.
• It is only possible to change one type of atom into another through
nuclear processes such as take place in a nuclear power plant, the
sun, atomic bombs or particle accelerators.
• The elements do not change in ordinary chemical reactions.
Periodic table
The very useful tool for every chemist is the periodic table, which lists all
the elements. It is not a simply list; it arranges the elements by number of
electrons. The electrons in the outer electronic shells are responsible for many of
the properties. Hence, elements in a single column tend to have similar
properties to each other.
The Periodic Table
1
H
2
He
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11
Na
12
Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31
Ga
32
Ge
33
As
34
Se
35
Br
36
Kr
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47
Ag
48
Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79
Au
80
Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
87
Fr
88
Ra
89
Ac
104
Rf
105
Db
106
Sg
107
Bh
108
Hs
109
Mt
110
Ds
111
112
113
114
115
116
117
118
58
Ce
59
Pr
60
Nd
61
Pm
62
Sm
63
Eu
64
Gd
65
Tb
66
Dy
67
Ho
68
Er
69
Tm
70
Yb
71
Lu
90
Th
91
Pa
92
U
93
Np
94
Pu
95
Am
96
Cm
97
Bk
98
Cf
99
Es
100
Fm
101
Md
102
No
103
Lr
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Here we said it. The atom contains electrons. There are smaller particles
inside an atom. What are they?
These smaller components, electrons, protons and neutrons are called
subatomic particles.
Subatomic Particles
Most of matter is made of three subatomic particles:
Particle
Symbol
Relative Relative Location
Charge Mass
Electron e-
-1
1
p+
+1
1836
Electron
Cloud
Nucleus
0
1839
Nucleus
Proton
Neutron n0
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Some of the electrons form the element can be relatively easily removed. In
some cases additional electrons can be added to the elements. Such elements
with altered number of electrons are called ions.
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Usually atoms have the same number of electrons as protons so the
charges cancel each other out.
Sometimes an atom can have more or fewer electrons than protons
resulting in a net positive or negative charge. When this happens it is called
an ion.
Example: Sodium (Na) looses an electron to form Na +
Chlorine can gain an electron to from ClWe can tell what type of charge an ion is expected to have by looking at
where it is in the periodic table.
Some elements can have same number of protons and electrons, but they
can differ in the number of neutrons. Such elements are called isotopes.
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Atoms with the same number of protons but different numbers of neutrons
Deuterium, tritium, carbon 12, U235
Some isotopes are radioactive while others are stable
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