Chemical formulas are used to describe molecules and compounds. In chemical formulas the abbreviations of element names, which are listed in the periodic table, are used. For example, "H" represents one atom of hydrogen and "O" represents one atom of oxygen. If we want to represent two atoms of hydrogen, instead of writing H H, we write H2. The subscript "2" means that two atoms of the element hydrogen have joined together to form a molecule. A subscript is only used when more than one atom is being represented, that is a subscript of "1" will never be seen in a chemical formula.

Isotopes:  Isotopes are a form of an element that has the same number of protons but a different number of neutrons. In general, atoms want to have the same number of neutrons and protons but the number of neutrons can change. Notice that the three hydrogen atoms have the same number of protons, but a different number of neutrons. Different isotopes of an element are present in different proportions in nature. For example, light hydrogen which has no neutrons, is the most common isotope of hydrogen. The nuclear symbols of the 3 hydrogen isotopes are as follows:

H₁¹      H₁²     H₁³    

In the nuclear symbols above, the superscript represents the mass number while the subscript represents the atomic number. From these two quantities the number of neutrons present in the isotope can be calculated.

Ionization: An ion is an atom, group of atoms, or a particle with a positive or negative charge. Ionization is any process that changes the electrical balance within an atom. If we remove an electron from a stable atom, the atom becomes electrically incomplete/unbalanced. That is, there are more protons in the nucleus (positive charges) than there are electrons (negative charges). With an electron removed, the atom possesses a plus one charge, therefore it is a positive ion. Consequently, the liberated electron is a negative ion, as long as it exists by itself and does not combine with another atom. One way ionization occurs is through radiation.

Atoms are held together by a binding energy. This means that the electrons are held in their electron shells by a quantity of binding energy. In order to liberate an electron from its parent atom, it will take energy that is at least equal to the binding energy that holds the electron. The amount of ionization that occurs is dependent upon two main factors, (1) the radiation energy, and (2) the type of material the radiation is interacting with. The process of ionization will be discussed more in depth in the X-rays module.

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Pharmaceutical Analytical Chemistry

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