Periodic Table3

The elements in vertical columns of the periodic table have similar chemical properties. The sets of elements are called groups or families. Some of the families have historical names that pre-date the modern periodic table, since their chemical similarities were noted before the table was widely accepted.

· Alkali metals—the metallic elements in group 1 are called the alkali metals because they react with water to form alkaline solutions. Note that hydrogen, though it is in group 1, is not an alkali metal. The alkali metals are yellow in the periodic table above.

· Alkaline earth metals—the elements in group 2 have properties similar to those of group 1 but are slightly less reactive, hence “earthy.” The alkaline earth metals are black in the periodic table above.

· Chalcogens—the non-metals and semi-metals in group 16 are called chalcogens from the Greek word for ore because a great many ores are oxides, sulfides or telurides. Note that polonium is a metal and has very different properties from the other members of group 16. This is the only traditional group name that you won’t be expected to know in most freshman chemistry courses.

· Halogens—the elements in group 17 are known as the halogens (‘salt former’ in Greek) because they easily form negative ions (which are found in the class of compounds called salts). The halogens are blue in the periodic table above.

· Noble or inert gases—the elements in group 18 are known as noble gases because they do not readily form compounds. The word noble, in this context, is the opposite of the word 'base,' or easily corruptible. The noble gases are green in the periodic table above.

Groups are numbered from left to right across the periodic table. For example, carbon is in group 14. Older designations used Roman numerals and the letters A and B to identify the groups. Unfortunately, while these systems are still in use, the letter designations in the United States and in Europe are NOT the same.

The terms 'group' and 'family' used to be synonymous. This posed a problem when considering elements like hydrogen and bismuth. These and other elements have properties that follow periodic law yet are different from those of the elements in the same horizontal column of the periodic table. The term group has been expanded to mean a collection of elements with similar physical and chemical properties that may or may not be in the same 'family.' The periodic table above is color coded by the nine accepted elemental groups:

alkali metals	yellow
alkaline earth metals	black
transition metals	white
inner transition metals	red
other metals	purple
semi-metals	brown
other non-metals	orange
halogens	blue
noble gases	green

The elements in horizontal rows of the periodic table have atoms with the most similar sizes. Periods are numbered from 1 through 7. The two horizontal rows found at the bottom of the periodic table are actually inside periods 6 and 7.

Answer: Tin is in group (family) 14 and in period 5. Tin is also in the set of elements known as 'other metals.' Students have to rely on context to decide if the word 'group' refers to a column on the periodic table or to a set of elements with similar properties that may or may not be in the same column on the periodic table.

04/25/09

Periodic Table: Periods and Groups

Groups

Groups or families