Clarke Earley, Ph.D.
Department of Chemistry
Kent State University Stark Campus
North Canton, OH 44720
The periodic table is divided into two major divisions: metals and non-metals. Metals (shown below in yellow) are located on the lower left and include typical metals such as iron (Fe) and nickel (Ni). Non-metals (shown in blue) are located in the upper right and include oxygen and nitrogen (common gases) as well as iodine (a solid). The position of elements on the periodic table can to used to predict with a high degree of accuracy the structure of a wide range of compounds.
A binary compound is one that is formed from two types of elements. Three possibilities exist.
|metal + metal||--→||metallic compound|
|metal + non-metal||--→||ionic compound|
|non-metal + non-metal||--→||covalent compound|
The physical properties of each of these types of compounds is summarized below.
(solutions do conduct)
For simple binary compounds, it is possible to predict the formula of many ionic compounds by following the rules listed here.
For example, if magnesium (Mg) and bromine (Br) are mixed:
Thus, the formula of the ionic compound formed is MgBr2.
In this image, the ions are represented as spheres, and a pair of ions is circled that corresponds to the ionic formula (NaCl). However, this choice is NOT unique: almost any pair of ions could have been selected. In solution, these ions will separate completely to create an electrically conductive solution. Water-soluble ionic compounds that dissolve in water to give conducting solutions are called electrolytes.
Notice in this image that the individual molecules (represented as sticks) do not touch or bond with other molecules. Attraction forces between molecules (intermolecular forces) do exist, but are much weaker than the attractions (bonds) between atoms within a molecule.