Chapter 1: Atoms, Molecules and Molecular States
Gary Harris & J.A. Griffin
Howard University
gharris@msrce.howard.edu & jagriffin@howard.edu
Cancer and the way in which we treat cancer is about to change forever. Imagine if you
were informed when the first cell in your body became cancerous. Doctors could almost
guarantee a speedy recovery and cure. Nanotechnology will allow us to act on
information like this.
Today the heart of a computer is based on what is called transistor technology and
building these transistors requires “top down” technology (carving transistors out of
pieces of silicon using lithography techniques). How about assembling computers using
individual molecules and atoms? Clearly, these computers would be smaller and thereby
faster.
Specific manipulation of surfaces for new effects and improvement of surface properties
are leading to corrosion protection (the deterioration caused by chemical reaction with
the environment, affects materials as different as structural metals, ceramics, and wood,
as well as works of art and artifacts from past civilizations), abrasion resistance (no
superficial damage to the surface at all), photo-catalysis (this technique utilizes nanosize particles to carry out oxidation to disassemble volatile organic compounds into
common gases), and antigraffti surfaces (surfaces that can’t be painted or written on) that
have added new functionality though nanotechnology.
Nanotechnology is the understanding and control of matter at dimensions of roughly 1 to
100 nanometers, where unique phenomena enable novel applications [1]. A nanometer is
one billionth of a meter. The prefix “nano” comes from a Greek word meaning dwarf.
Encompassing nanoscale science, engineering and technology, nanotechnology involves
imaging, measuring, modeling, and manipulating matter at this length scale. There is no
field of science and engineering that is not impacted by nanotechnology. Atoms and
molecules are the building blocks of all matter.
Matter
“Atoms are letters. Molecules are the words” [2]. All stuff or matter is composed of
atoms. Matter is defined as anything that has mass and occupies space. There are three
basic forms of matter: solid, liquid and gas. Solids include things like glass, metal,
stones and rocks. They are fixed in shape and occupy space. Liquids such as water, soda,
oil and alcohol also occupy space, but their shape changes depending on the shape of the
vessel in which they are stored. Gases such as air, helium, and natural gas seem to
Chapter 1: Atoms, Molecules and Molecular States
Gary Harris & J.A. Griffin – Copyright March 2007
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occupy no space, but they have both mass and volume. To make things interesting, some
things like water commonly exist in all three forms or states (water, ice and steam).
The unique character of the way matter reacts with other matter is due to their properties.
These properties are grouped into two classes: physical and chemical. Physical
properties are special characteristics that make up the physical composition of a sample.
These properties can also change at the nano level. Physical properties include: form,
density, thermal and electrical conductivity, melting and boiling point, etc.
Chemical properties are those characteristics that focus on the substance’s behavior when
mixed with different elements or compounds. Chemical properties are also a function of
the size of the elements. Nanosize particles react differently. Size and scale often affect
how matter behaves in surprising ways. As size or scale approach the nano-region,
behavior is difficult to predict using classical theory.
Atoms are the smallest unit of substances and these atoms are in constant motion and
interact with other atoms to form molecules. The arrangement of these building blocks
gives materials their many properties like mechanical strength, ability to conduct
electricity, melting point, etc. An atom is composed primarily of three fundamental
parts: electrons, protons and neutrons. The combination of these parts and the number of
these parts is unique for every element known to exist in the universe. Each element has
a known unique number of protons and electrons. Protons are particles with a positive
(plus) charge. Electrons are particles with a negative (minus) charge. Under normal
conditions an atom is neutral (equal number of positive and negative charges). An
element with five protons is boron. How many electrons must it have to be neutral? The
answer is five.
The Elements
The Periodic Table of Elements is a very useful table for describing the atoms of every
known element. The lightest elements are hydrogen and helium. All the heavier
elements are made, both naturally and artificially. Every known element has a nickname,
which consist of one-to-two letters. For instance, C is the nickname for carbon. An atom
of carbon has six protons and six electrons. The number of protons in an atom of an
element is called its atomic number. The Periodic Table of Elements can be used to
determine the number of electrons in a neutral atom of copper (Cu). Neutrons are large
and heavier than electrons and protons and have no electrical charge. Since the total
charge of an atom is zero, an atom normally has an equal number of electrons and
protons under normal conditions. Not all atoms of the same element have the same mass.
These different forms of the same element are known as isotopes. For instance, carbon12 and carbon-13 both have six protons and six electrons, but the number of neutrons in
each is 6 and 7 respectively.
Chapter 1: Atoms, Molecules and Molecular States
Gary Harris & J.A. Griffin – Copyright March 2007
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The nucleus is where the protons and neutrons hang out. Sometimes this nucleus can
behave like a small magnet and line-up in a magnetic field. This magnetic property of
the nucleus is called the magnetic moment and is important in detecting these nuclei
when using a magnetic field.
The elements of the periodic table are placed in specific rows and columns because of the
way they look and act. If you have ever looked at a grid, you know that there are rows
(left to right) and columns (up and down). The periodic table has rows and columns, too,
and each one means something different. Each row in the table is considered to be a
different period. Elements have something in common if they are in the same row. All
of the elements in a column have the same number of outer electrons.
A Danish physicist, Neils Bohr, came up with a model that pictured the atom with a
nucleus made up of protons and neutrons in the center and electrons spinning in an orbit
around it, like the Sun and Planets. The electron, which is 1836 times lighter than the
proton, has a negative charge and the proton has an equal positive charge. Remember
that the third subatomic particle, the neutron has no charge but is heavier than both the
electron and proton. According to Bohr’s Theory, an orbit is the path that an electron
follows as it moves around the nucleus. The orbits appear as a series of concentric
circles with their centers located at the nucleus. The Bohr model for hydrogen (H) is
shown below.
The simple Bohr Model has evolved because small subatomic matter has something
called duality. That is to say that atomic and subatomic matter can act like both waves
and particles. This field of study is called quantum mechanics and is a theoretical
mathematical approach to the study of atomic and molecular structures. Quantum
Mechanics is a very complex theory. Classical mechanics has its foundation in Newton’s
Laws of Motion. Classical mechanics does a great job of describing and predicting
things at the macroscopic scale (large world view). This would include things like cars,
trains, bullets, football flight, etc. These laws can describe things that you can see with
the naked eye. However, when things get small like on the nanoscale size (10-9 m or one
billionth of a meter), Newton’s Laws of Motion do not predict the behavior of this type of
matter. The point at which an aggregation of particles becomes more accurately
described by classical physics than by quantum mechanics is known as the classical limit.
Chapter 1: Atoms, Molecules and Molecular States
Gary Harris & J.A. Griffin – Copyright March 2007
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The wave properties of matter form the basis of quantum mechanics. The term “quantum
mechanics” is used because wave mechanics predicts only certain allowed energies,
called quantum states. In the ocean, the wind produces waves whose crests and troughs
move across the water. The distance between the peaks of the waves is called the
wavelength (λ). The waves also have height and frequency. These are examples of
traveling waves. DeBroglie proposed that not only does light have the dual properties of
waves and particles, but atoms and molecules do also. The wavelength of these particles
is given by: λ=h/mv where m and v are the mass and velocity of the particle and h is
Planck’s constant. The mathematical solution to the wave equation for electrons must
satisfy three quantum conditions corresponding to three dimension of space. Each
quantum condition introduces an integer, called a quantum number. The three principle
quantum numbers are usually designated as follows:
•
n, principal quantum number, exclusively determines the energy orbital
•
l, angular momentum quantum number determines, the shape of the orbital
•
ml, magnetic quantum number, determines orientation of the orbital in space
•
ms, a fourth quantum number that takes into consideration the electron spin, electrons
spin, clockwise and counter clockwise about the orbital in space.
Quantization is not a difficult thing to understand because it exists in lots of every day
examples. For example, money is not quantized, but coinage money is quantized and the
minimum quantum coin in the US is a penny.
The first quantum number says that electrons can only be in "special" orbits. All other
orbits are just not possible. They could "jump" between these special orbits, however,
and when they jumped they would wiggle a little bit, producing radiation. The radiation
is characteristic of the wiggle between the energy levels. The Pauli exclusion principle
states that no two electrons in an atom may have the same set of all four quantum
numbers and helps set the conditions for the radiation (wiggle) between energy levels.
Chemical Bonding
Molecules are collections of atoms bound to each other that exist in the three phases.
The electrons located in the outermost energy level of an atom play a major role in
determining the atom’s chemical properties. These outermost electrons are called
valence electrons. Thus the oxygen that we breathe is a molecule made up of two oxygen
atoms combined and written as O2. Atoms can combine in several ways to form
molecules. One way, is by sharing valence electrons to make a more stable compound.
This type of grouping is called a covalent bond. This type of attraction can hold
molecules together. Remember from Superman that diamond is the strongest material
Chapter 1: Atoms, Molecules and Molecular States
Gary Harris & J.A. Griffin – Copyright March 2007
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known to man. The carbon atoms in diamond form covalent bonds. Another way of
forming molecules is by transferring electrons between two atoms. One atom will gain
an electron and the other atom will lose an electron. This type of bonding is called an
ionic bond. Table salt, (sodium chloride NaCl) is an example of an ionic compound. Na
+ and Cl- ions are packed together in equal concentrations. The sum of the ionic charges
in the formula is always zero. A different type of bonding exists in metals. In metals, all
the atoms share all the electrons at one time. Thus metals easily conduct electricity
because an extra electron can be added or removed without removing it from a single
discrete atom. These materials are shiny, malleable and good conductors of heat and
electricity. Most metals are on the left hand side of the periodic table. There are other
types of bonding which are important in nanotechnology. Molecules and atoms can be
drawn together by relatively weak forces collectively called van der Waals forces or
interactions. These three forces are London forces sometimes called dispersive forces,
dipole-dipole forces and hydrogen bonding.
Nonpolar (non-charged) compounds do form solids, but at very low
temperatures. Very weak attractions called dispersion forces occur
when temporary dipoles form within nonpolar molecules.
Remember that electrons in molecules are not always distributed
symmetrically. For polar molecules, attractive forces called dipoledipole attraction occur between the positive end of one molecule
and the negative end of another. These partial charges attract
neighboring H-Cl molecules as shown in the diagram: dipoledipole forces are shown in green. The strength of these attractions
increases with increasing polarity of the molecules.
Hydrogen bonds occur between very specific types of atoms and molecules. In certain
polar molecules, strong dipoles occur when a hydrogen atom is attached to an atom of
fluorine, oxygen, or nitrogen, all of which have high electro-negativity values. Although
these hydrogen bonds are weak, they can play an important role in the structure and
behavior of matter, like water. These bonds also play an important role in at least two
strands of DNA.
Self-Assembly
Molecular self-assembly is the assembly of molecules without guidance or management
from an outside source. Self-assembly can occur spontaneously in nature, such as the
self-assembly of the lipid bilayer membrane. The process of self-assembly in nature is
governed by inter-molecular and intra-molecular forces that drive the molecules into a
stable, low energy state. These forces were discussed earlier and include hydrogen
bonding, electrostatic interactions, hydrophilic interactions and van der Waals forces.
Self-assembly is thus referred to as a ‘bottom-up’ manufacturing technique, as compared
to lithography being a ‘top-down’ technique (lithography is the method of creating small
Chapter 1: Atoms, Molecules and Molecular States
Gary Harris & J.A. Griffin – Copyright March 2007
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structures from a large block of matter).
There are two major approaches possible for molecular self-assembly. The two strategies
are: electrostatic self-assembly (or layer-by-layer) and self-assembled monolayers (SAM).
Electrostatic self-assembly involves alternate absorption of anionic (+) and catonic (-)
electrolytes into suitable substrates. The latter strategy of self-assembled monolayers
(SAMs) is based on thiols and silanes. Thiols are organic compounds that contain a
functional group composed of a sulfur atom and a hydrogen atom (-SH). This functional
group is referred to as either a thiol group or a sulfhydryl group. More traditionally,
thiols are often referred to as mercaptans. Silane is a chemical compound with a
chemical formula SiH4 (silicon and four hydrogen atoms). It is the silicon analogue of
methane. Silanes consist of a chain of silicon atoms bound to hydrogen atoms.
H
Nanotechnology and Society
How does society determine who, what, when, where, and how to use its technological
knowledge and inventions? Nanotechnology is driven by the aim to advance broad
societal goals. What are some of the practical implications and cultural context of
nanotechnology research and development and how will these impact the US and the
world? The world must be concerned about:
•
•
•
•
environmental safety and health impact of nanotechnology.
educational opportunities in this growing new field of science.
broad impact on ethical and legal issues.
who will own this technology.
An excellent report exploring the potential societal impacts of nanotechnology has been
edited by Mihail C. Roco and William S. Bainbridge of the National Science Foundation.
Some Nanotechnology Products
As of November 26, 2006 there are over 356 products or product lines that are based on
nanotechnology. One of my favorite products is the new Samsung front-loading washer
which uses Silver Ions in its wash and rinse cycles to kill 99.9% of tested bacteria to
sanitize laundry, all in cold water without the use of bleach. Samsung developed a
system to use Silver, widely known for its anti-microbial properties, in the wash water of
its newest line of washing machines. Metallic silver atoms, electrolytically stripped of an
electron, are injected during the wash and rinse cycles, allowing over 100 quadrillion
silver ions to penetrate deep into the fabric to sanitize clothing without the need for hot
water or bleach. Clarity Fog Eliminator by NanoFilm Ltd. is a coating that will protect
and prevent fog on glass surfaces. NanoFilm's nanotechnology pursuits in optical lenses
include self-assembled top coatings for non-reflective lenses to both seal and repel dirt,
dust and skin oils from the fragile inorganic anti-reflective (AR) layers.
Chapter 1: Atoms, Molecules and Molecular States
Gary Harris & J.A. Griffin – Copyright March 2007
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One of the oldest applications that employed nanotechnology was used by the cowboys
when they would put a Silver Dollar in the bottom of their canteens. The silver
prevented bacteria from growing in the water from the creek.
References
1. National Nanotechnology Initiative, http://www.nano.gov/html/facts/whatIsNano.html
2. Nobel Prize interview: http//nobelprize.org/chemistry/laureates
Additional Reading
1. Ted Sargent, “The Dance of the Molecules”, 2006.
2. George Whitesides and Bartosz Grzybowski, “Self-assembly at All Scales,” Science,
29 March 2002, vol. 295, pp2418-21.
3. Robert F. Service, “Nanotechnology Grows Up”, Science, vol. 304, 18 June 2004, pp
1732-34.
4. “Nanotechnology: Societal Implications—Maximizing Benefits for Humanity,” Edited
by Mihail C. Roco and William S. Bainbridge of the National Science Foundation,
December 2003.
5. Nanoproducts: http://www.nanotechproject.org/index.php?id=44
6. Mick Wilson, Kamali Kannangara, Geoff Smith, Michele Simmons and Burkhard
Raguse, Nanotechnology-basic science and emerging technologies, 20004, Chapman &
Hall/CRC.
7. Various Authors, “Understanding Nanotechnology”, Scientific American, 2002.
8. Learn more visit: www.nnin.org
9. For younger students: www.nanooze.org
10. Interdisciplinary Education Group: http://mrsec.wisc.edu/Edetc/index.html
11. The Search for DNA - The Birth of Molecular Biology:
http://www.accessexcellence.org/RC/AB/BC/Search_for_DNA.html
Chapter 1: Atoms, Molecules and Molecular States
Gary Harris & J.A. Griffin – Copyright March 2007
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12. DNA: The Instruction Manual for All Life:
http://www.thetech.org/exhibits/online/genome/
Chapter 1: Atoms, Molecules and Molecular States
Gary Harris & J.A. Griffin – Copyright March 2007
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