The microscopic structure of matter

© 2013 by  Fernando Caracena


It is no secret to anybody in the 21st Century that matter is made up of atoms and that there are subatomic particles that make up the atom; further, that the atom can be split with explosive results. Modern person has also heard about molecules, which are structures made up of atoms, sometimes only a few, such as in water, but sometimes in very large numbers, such as in biological molecules, e. g., as in DNA. Further, the modern person knows that all the other stuff that we see with our eyes, smell with our nose, taste with out tongue or hold in our hand is made up of molecular stuff.

Atoms hypothesized from chemistry

Atoms and molecules explain the action of chemicals—the laws of chemistry. In fact, they were hypothesized in chemistry to make sense out of how chemical reactions work.

In the early part of the 19th Century, John Dalton (1766–1844) found that the existence of chemical elements and their properties could be well explained by the hypothesis that each chemical element was composed of identical atom in large numbers, and different chemical elements were composed of different atoms. Dalton pictured chemical compounds as identical “molecules,” each composed of combinations of atoms in composite structures. The atomic and molecular hypothesis very neatly explained the basic laws of chemistry.

Atoms of classical Greek philosophy

The name atom itself represents a first attempt by a school of Greek philosophy to come up with a theory of everything, the  atomists: Leuccipus, Democritus, and Lucretius.

The atomists had suggested that everything in the universe is made up of microscopic atoms (indestructible bits of matter beyond the range of human senses) moving about in the void (empty space). As they conceived them, atoms could not be broken down further because they were so hard that they were able to resist any possible fracture. The idea of a binary, being-non-being basis from the universe is not a logial concept. It postulates the existence of nonexistence (the void), which is logically inconsistent. It violates the rules of standard logic.

Had the atomists lived long enough to see the discoveries of the 20th Century in physics, they would have been very happy to see their ideas about the atomic structure of matter verified; but had they continued to live into this century, they would have been very unhappy to see the whole scheme dissolve into many fundamental particles and eventually, into strange string-like forms and multiple dimensional spaces.

The structure of atoms according to physics

Modern physics has developed methods of probing the structure of matter on progressively smaller scales, even to the point of imaging and manipulating individual atoms using electron microscopes. What is really imaged about an atom is the electron cloud that surrounds the nucleus of an atom. Observations of atoms confirm the ideas about the structure of atoms that had been put together from earlier physics experiments of the 20th Century and quantum theory.

The atom at normal, room temperature is an electrically neutral structure that consists of charged particles. Most of the size of the atom is generated by a cloud of orbiting electrons, each of which carries one negative electronic charge unit(-e). The nucleus of the atom, which is about 10-5 (0.00001) times the size of the electron cloud, contains most of the mass of the atom and an equal number of positive electronic charges units that electrically balance the net charge of the atom to zero. An electric force between the nucleus and the orbiting electrons holds the atom together.

The atomic nucleus is composed of two particles called nucleons, which are protons that carry one unit of positive charge(+e) and act like magnets, and neutrons that although they carry no charge act like magnets. The electric repulsion of protons would not allow the nucleus to remain intact, were it not for an even stronger force that acts over short distances on the scale of the nuclear size. This is the strong nuclear force. Another force, called the weak nuclear force, also restricted to the nuclear scale, is not important to this discussion and will be discussed in a later blog. So far, physicists recognize four fundamental forces: gravity, the electromagnetic interaction and the weak and strong nuclear forces.   Protons and neutrons are close to being of equal mass and they tend to occur in a nucleus in about equal numbers, plus or minus a few extra neutrons.

The number of protons in the nucleus controls the chemical properties of the element that that type of atom makes up in huge numbers. For example, the simplest kind of atom, the hydrogen atom, makes up the element hydrogen, which at room temperature is a gas that is lighter than air and very explosive. The Hindenburg Zeppelin was an blimp-type airship that was made lighter than air by gas bags of hydrogen. While landing in New Jersey, some spark set off the hydrogen, which burned explosively. This famous air disaster demonstrates the explosive nature of hydrogen burning in an atmosphere that contains oxygen. The product generated by such an explosive reaction is ordinary water, which firemen use to put out flames.

Atomic number

The number of protons in the nucleus of an atom, of which an element is composed, is called the atomic number. The number of chemical elements is close to 120 on the atomic number scale and their chemical properties arrange themselves in a periodic array, called the periodic table. For each element the neutron number can vary generating element components of different mass, called isotopes, which have similar chemical properties. For example, there are three isotopes of hydrogen: ordinary hydrogen(nucleus composed of 1 proton), deuterium (nucleus composed of 1 proton + 1 neutron) and tritium (nucleus composed of 1 proton + 2 neutrons). Naturally occurring hydrogen contains a mixture of the three isotopes listed, the latter two being present in very small trace amounts.

A naive approach to chemistry would lead to the expectation that to the extent that we can discount the mass of the electron, all elements would have masses that were integral multiples of the mass of simple hydrogen. However, the presence of isotopes and mass effects produced by the binding of nucleons ruin such a simple scheme.

This entry was posted in electricity and magentism. Bookmark the permalink.

Leave a Reply

Your email address will not be published. Required fields are marked *