ATOMIC NOTATION

a. In order to simplify discussions concerning elements and atoms, a standard notational form is used to talk about atoms. It is based upon the primary characteristics of the atom. The first of these characteristics is the number of protons in the nucleus of the atom, which in a neutral atom is also the number of electrons in shells around the nucleus. This number, which determines the element to which the atom belongs, is called the atomic number. It is usually symbolized by the capital letter "Z." The second primary characteristic is the number of neutrons in the nucleus, a factor which, to some degree, determines the nuclear characteristics of the atom. The number of neutrons in the nucleus is described in terms of the total number of major particles in the nucleus; the total number of nucleons (sum of neutrons and protons) is called the atomic mass number. It is usually symbolized by the capital letter "A." Therefore, the number of neutrons is given by A - Z. In addition, each element has its own symbol or abbreviation, such as "H" for hydrogen or "Fe" for iron. The standard notation takes the following form:



b. Using this notation, an atom can be easily described. For example, the atomic notation at the right is for an atom with 92 protons (uranium--symbol U), 92 electrons in shells around the nucleus, and a total of 235 nucleons in the nucleus. Since 92 of the nucleons are protons, there are 143 neutrons in the nucleus of this atom.

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