NUCLEAR PHYSICS
The nucleus of the atom is composed of particles called protons and neutrons,
which are collectively called nucleons. The number of protons in a given nucleus
is called the atom’s atomic number, or Z, and the number of neutrons (the neutron
number) is denoted N. The total number of nucleons, Z + N, is called the mass
number (or nucleon number), and is denoted A. The number of protons in the
nucleus of an atom defines the element. For example, the element chlorine
(abbreviated Cl) is characterized by the fact that the nucleus of every chlorine atom
contains 17 protons, so the atomic number of chlorine is 17; however, different
chlorine atoms may contain different numbers of neutrons. In fact, about three-
fourths of all naturally occurring chlorine atoms have 18 neutrons in their nuclei
(mass number = 35), and most of the remaining one-fourth contain 20 neutrons
(mass number = 37). Nuclei that contain the same numbers of protons but different
numbers of neutrons are called isotopes.
Periodic Tables
A periodic table will not
be provided on the test.
However, a question of
this nature will provide
you with all the pertinent
information needed.The notation for a nuclide—the term for a nucleus with specific numbers
of protons and neutrons—is to write Z and A, one above the other, before
the chemical symbol of the element.The isotopes of chlorine mentioned earlier would be written as follows:
and- How many protons and neutrons are contained in the nuclide?