The periodic table is the most important chemistry reference there is. It arranges all the known elements in an informative array. Elements are arranged left to right and top to bottom in order of increasing atomic number. Order generally coincides with increasing atomic mass.
There are 18 vertical columns, or groups, in the standard periodic table. At present, there are three versions of the periodic table, each with its own unique column headings, in wide use.
In chemistry, a group (also known as a family) is a vertical column in the periodic table of the chemical elements. There are 18 groups in the standard periodic table.
The periodic table groups are as follows (in the brackets are shown the old systems: European and American):
Group 1 (IA,IA): the alkali metals or lithium family
Group 2 (IIA,IIA): the alkaline earth metals or beryllium family
Group 3 (IIIA,IIIB): the scandium family
Group 4 (IVA,IVB): the titanium family
Group 5 (VA,VB): the vanadium family
Group 6 (VIA,VIB): the chromium family
Group 7 (VIIA,VIIB): the manganese family
Group 8 (VIII, VIIIB): the iron family
Group 9 (VIII, VIIIB): the cobalt family
Group 10 (VIII, VIIIB): the nickel family
Group 11 (IB,IB): the coinage metals (not an IUPAC-recommended name) or copper family
Group 12 (IIB,IIB): the zinc family
Group 13 (IIIB,IIIA): the boron family
Group 14 (IVB,IVA): the carbon family
Group 15 (VB,VA): the pnictogens or nitrogen family
Group 16 (VIB,VIA): the chalcogens or oxygen family
Group 17 (VIIB,VIIA): the halogens or fluorine family
Group 18 (Group 0, VIIIA): the helium family/neon family; for the first six periods, these are the noble gases
A period is a horizontal row in the periodic table. Although groups are the most common way of classifying elements, there are some regions of the periodic table where the horizontal trends and similarities in properties are more significant than vertical group trends. This can be true in the d-block (or "transition metals"), and especially for the f-block, where the lanthanides and actinides form two substantial horizontal series of elements.
History of Periodic Table
In 1869, a Russian chemist named Dmitri Mendeleev cameup with way of organizing the elements that were known at the time.
He set them out in order of atomic weight, and then grouped them into rows and columns based on their chemical and physical properties.
Mendeleev had no idea what atoms were made of or why they behaved as they did. Nevertheless, he was able to put together the periodic table almost as we know it today--except that some elements were missing, because they were unknown in 1869.
His basic rule was this: the elements in any column, or group, of the table are similar to their column-mates. For example, look at the first column on the left, underneath hydrogen (H). The elements in this group are called the alkali metals; they're all soft metals that react violently with water to make hydrogen gas.