Periodic table: Encyclopedia II - Periodic table - Groups

Periodic table - Groups

A group, also known as a family, is a vertical column in the periodic table of the elements. There are 18 groups or families in the standard periodic table. Elements in a group have similar configurations of their valence shell electrons, which gives them similar properties.

There are three systems of group numbers; one using Hindu-Arabic numerals (1, 2, ... 18), another using Roman numerals (I, II, ... VIII), and one using a combination of Roman numerals and Latin letters (IA, IIA, IB, ... VIIIA). The Roman numeral names are the original traditional names of the groups; the Arabic numeral names are a newer naming scheme recommended by the International Union of Pure and Applied Chemistry (IUPAC). The IUPAC scheme was developed to replace both older Roman numeral systems as they confusingly used the same names to mean different things.

In the group known as the halogens (17), the element chlorine (Cl) falls between fluorine (F) and bromine (Br). Despite their dramatic differences in mass, they have similar properties. They are all highly corrosive. Chlorine and fluorine are gases, while bromine is a very low-boiling liquid. Chlorine and bromine are brightly colored, although fluorine is not.

Adapted from the Wikipedia article "Groups", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki