The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping includes lithium (Li), sodium (Na), and potassium (K). All of these elements are shiny, conduct heat and electricity well, and have similar chemical properties. A second grouping includes calcium...

The periodic table of elements is an important reference in chemistry for organizing the elements. The table has seven rows, or periods, numbered top to bottom, and eighteen columns called groups or families.

While the modern numbering system recommended by the International Union of Pure and Applied Chemistry or IUPAC, numbers the group...