where X is the chemical symbol for the element. This representation is sometimes referred to as a
nuclide symbol. Note that since an element is defined by the atomic number, Z is technically
redundant information if one has access to the periodic table. Often, then, this quantity is omitted.
Examples: : a single proton; the nucleus of ordinary hydrogen.Number of neutrons = presuperscript – presubscript = 1 – 1 = 0.: the nucleus of ordinary helium, consisting of 2 protons and 2 neutrons. It is also
known as an alpha particle (α-particle, see below).
: a fissionable form of uranium, consisting of 92 protons and 235 – 92 = 143
neutrons.ISOTOPES
Different nuclei of the same element will by definition all have the same number of protons. The
number of neutrons, however, can be different. Nuclei of the same element can therefore have
different mass numbers. For a nucleus of a given element with a given number of protons (atomic
number Z), the various nuclei with different numbers of neutrons are called isotopes of that
element.
BASIC CONCEPT
All isotopes of a given element have the same value of Z, but different values of N and A.Example: The three isotopes of hydrogen are:: a single proton; the nucleus of ordinary hydrogen.
: a proton and a neutron together; the nucleus of one type of heavy hydrogen
called deuterium.
: a proton and two neutrons together; the nucleus of a heavier type of heavy