Atomic Structure

Atomic Structure

Before one can begin to understand the concept of nuclear fission, and consequently the significance of Lise Meitner's work, one must have an understanding of the nature of the atom itself.

Given the meaning of the word atom (Greek for indivisible), one can be forgiven for thinking that the concept of atomic structure is absurd. Indeed, up until the last century, atom were seen as indivisible, solid spheres. Then, during the great boom in research in atomic theory in the 19^th century, it was realised that atoms did indeed have separate, constituent parts.

However, it was only until 1932, with the discovery of the neutron by James Chadwick in England, that the field of nuclear research could begin.

Essentially, the atom can be seen as two spheres, one large, and a smaller one inside the larger. In the outer sphere, electrons, small, lightweight negatively-charged particles move about. This outer sphere is better known as the charge cloud, so named because of the rapidly moving electrons creating an entire region of negative charge. The number of electrons in an atom is called the Atomic Number, or Z. This defines what element the atom is.

The small inner sphere, called the nucleus, contains two types of particles: positively charged protons, and neutrally-charged neutrons, collectively known as nucleons. The total number of nucleons is known as the Mass Number, or A. As there are the same number of protons as there are electrons in each atom, one can deduct Z from A to find the number of neutrons. This determines what isotope of a given element the atom is.

For the rest of this discussion, we will largely ignore electrons, as their properties and functions are a question for Chemistry.


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