NUCLEAR PHYSICS AND REACTOR THEORY

ATOMIC NATURE OF MATTER

All matter is composed

EO 1.1STATE the characteristics of the following atomic particles, including mass, charge, and location within the atom:

a. Proton b. Neutron c. Electron

EO 1.2DESCRIBE the Bohr model of an atom.

EO 1.3DEFINE the following terms:

a. Nuclide c. Atomic number

b. Isotope d. Mass number

EO 1.4Given the standard notation for a particular nuclide, DETERMINE the following:

a. Number of protons

b. Number of neutrons

c. Number of electrons

EO 1.5DESCRIBE the three forces that act on particles within the nucleus and affect the stability of the nucleus.

Structure of Matter

Early Greek philosophers speculated that the earth was made up of different combinations of basic substances, or elements. They considered these basic elements to be earth, air, water, and fire. Modern science shows that the early Greeks held the correct concept that matter consists of a combination of basic elements, but they incorrectly identified the elements.

In 1661 the English chemist Robert Boyle published the modern criterion for an element. He defined an element to be a basic substance that cannot be broken down into any simpler substance after it is isolated from a compound, but can be combined with other elements to form compounds. To date, 105 different elements have been confirmed to exist, and researchers claim to have discovered three additional elements. Of the 105 confirmed elements, 90 exist in nature and 15 are man-made.

Another basic concept of matter that the Greeks debated was whether matter was continuous or discrete. That is, whether matter could be continuously divided and subdivided into ever smaller particles or whether eventually an indivisible particle would be encountered. Democritus in about 450 B.C. argued that substances were ultimately composed of small, indivisible particles that he labeled atoms. He further suggested that different substances were composed of different atoms or combinations of atoms, and that one substance could be converted into another by rearranging the atoms. It was impossible to conclusively prove or disprove this proposal for more than 2000 years.

The modern proof for the atomic nature of matter was first proposed by the English chemist John Dalton in 1803. Dalton stated that each chemical element possesses a particular kind of atom, and any quantity of the element is made up of identical atoms of this kind. What distinguishes one element from another element is the kind of atom of which it consists, and the basic physical difference between kinds of atoms is their weight.