The Nucleus A Chemists View

Atomos, the Greek root of the word atom, means indivisible. It was originally believed that the atom was the ultimate indivisible particle of which all matter was composed. However, as we discussed in Chapter 2, Lord Rutherford showed in 1911 that the atom is not homogeneous but instead has a dense, positively charged center surrounded by electrons. Subsequently, scientists learned that the nucleus of the atom can be described as containing neutrons and protons. In fact, in the past three decades it has become widely accepted that even the protons and neutrons are composed of smaller particles called quarks. 

For most purposes, the nucleus can be regarded as a collection of nucleons (neutrons and protons), and the internal structures of these particles can be ignored. Recall that the number of protons in a particular nucleus is the atomic number (Z) and that the sum of the neutrons and protons is the mass number (A). Atoms that have identical atomic numbers but different mass number values are called isotopes. The general term nuclide is applied to each unique atom and is represented by zX, where X represents the symbol for a particular element. 

Since the chemistry of an atom is determined by the number and arrangement of its electrons, the properties of the nucleus are not of primary importance to chemists. In the simplest view, the nucleus provides the positive charge to bind the electrons in atoms and molecules. However, a quick reading of any daily newspaper will show you that the nucleus and its properties have an important impact on our society. This chapter considers those aspects of the nucleus about which everyone should have some knowledge. 

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