Nanotechnology and Human Health

Structure of Matter at the Nanoscale

Now that we have descended to the nanoscale and have a good sense of how small this world is, we can talk about the structure of matter. Here, I focus on four principles:

1. All tangible things are made up of atoms.
2. All atoms are in constant motion.
3. Molecules, which are collections of atoms that are bound together, have size and shape.
4. Molecules that are in pieces of matter with nanometer-scale dimensions sometimes have unexpected properties.

All Tangible Things Are Made Up of Atoms

Atoms are the underlying and essential building blocks of matter: matter is any physical substance that occupies spaces and has mass. The tangibles that are made up of atoms include large objects such as the sun, the earth, and the moon. Obviously these would be made up of an incredible number of atoms. To illustrate the point of how small atoms are, one million atoms could be laid across the head of an average pin. One molecule of water contains 3 atoms: 2 hydrogen and 1 oxygen; a buckyball consists of 60 atoms; one cubic centimeter of air, which is about the size of a sugar cube, contains approximately 10 ¹⁹ atoms. ¹¹ With that in mind, the number of atoms in the sun, earth, or moon is unimaginable.

Atoms Are in Constant Motion

It might be surprising to you to learn that ice, which is frozen water and appears to be a motionless solid, contains molecules that are in constant rapid motion. The molecules in frozen water are constantly moving in the form of vibrations. We cannot detect the vibratory movements with our naked eyes, because movements at the nanoscale level and below are impossible to see without help from special types of microscopes (which are discussed later in this unit). The motion at the nanometer scale is atomic motion; therefore, it is difficult to see the motion of a particular atom because, first, atoms are virtually indistinguishable, second, the movements are very rapid and, third, there is an enormous number of atoms packed together in any given object.

Molecules Have Size and Shape

Atoms come together to form molecules through intramolecular chemical bonds, which are very strong and usually cannot be broken without the input of considerable energy. There are two kinds of intramolecular bonds: ionic bonds and covalent bonds. In covalent bonding, the atoms share electrons equally. Ionic bonds are based on the concept that opposites attract. To understand the basis of this attraction of opposites, it is helpful to understand the make-up of atoms. Atoms are made of subatomic particles: protons, neutrons, and electrons. Neutrons, as the name suggests, are neutral and have no electrical charge. Protons have a positive electrical charge. Protons and neutrons are collected within the nucleus of the atom. Electrons circle the nucleus of the atom and have a negative electrical charge. Atoms that do not have the same number of electrons and protons are called ions. If an atom has more protons than electrons the atom has a positive charge. On the other hand, if an atom has more electrons than protons, the atom has a negative charge. Protons and electrons are electrically attracted to each other (opposites attract): an ion with a positive charge will be attracted to an atom with a negative charge. When atoms bond together, either by ionic or covalent bonding, they produce larger building blocks of matter that are called molecules. Chemical reactions primarily involve atoms or groups of atoms and interactions between their electrons. An example of a molecule formed by ionic bonding is table salt or NaCl - sodium chloride; an example of a molecule formed by covalent bonding is water or H ₂O.

Molecules generally have a certain shape due primarily to the way the atoms bond together. The angle of the bond that holds the hydrogen atoms to the oxygen atom causes water molecules to have the same shape. Larger molecules have more complex shapes. Often it is the shape of a molecule that contributes to its function because its shape results from the atoms and their intermolecular bonds and interactions. ¹²

Molecules at the Nanoscale Have Unexpected Properties

At the molecular level gravity is no longer the dominant force. Electrostatics (charge interactions) and surface tension become more important. At the nanoscale small particles interact with light differently and ultimately can become colorless. Gold turns a different color at different sizes on the nanoscale. Gold progresses from the gold color we know it as to blue, red, yellow, and then colorless as it gets smaller on the nanoscale. ¹³ This is due to the diffraction, or bending, of light. The different sized particles diffract different colors of light. Gold particles at 25 nanometers in size diffract the color red. ¹⁴ The nanoworld can best be described as a sticky environment because electromagnetism is the dominant force. The phenomenon of static electricity is a visible illustration of electromagnetic interaction. Keep in mind that atoms are in constant motion, therefore when molecules come in close proximity to one another they stick together through what is know as weak interactions. ¹⁵ Weak interactions can be further explained by van der Waals force. It is defined as weak intermolecular bonds that result from the temporary attraction of electrons. The constant movement of electrons within molecules causes electrostatic attraction, what we often refer to as static electricity when we experience a shock while walking across a carpet. When the electrons move the attraction is eliminated, causing only a temporary intermolecular bond. ¹⁶