The Periodic Table is organized with elements specified in rows, or periods, according to increasing atomic number. Metals are on the left of the periodic table, while nonmetals are located on the right. Some in the middle are called metalloids because they have characteristics of both metals and nonmetals. The periodic table is purposely arranged into vertical classifications called groups. Columns of elements help define element groups. Some of the notable groups of elements include the noble gases (column 18), the halogens (column 17), the alkali metals (column 1) and the alkaline earth metals (column 2). The transition metals are located in the center of the periodic table. They include many of the common metals, such as copper, iron, silver and gold. The two rows below the main body of the table are called the lanthanide and actinide series. They include the very heavy metallic elements, such as uranium and plutonium. This program goes in depth regarding the elements potassium (K) and magnesium (Mg) and their roles in the health of the human body. Potassium helps to control the proper balance of fluids in cells, helps with the contraction of muscles, and is involved in the transmission of chemical messages between nerve cells. Potassium aids in digestion of food, and in the proper function of the eyes. Magnesium is needed for more than 300 biochemical reactions in the body. It helps maintain normal muscle and nerve function, keeps heart rhythm steady, supports a healthy immune system, and keeps bones strong.