ElementsWhy group elements into families?
An element's chemistry depends mostly on its outer electrons. Elements with the same outer arrangement react in similar ways, so knowing the family tells you a lot before you know anything else. If you know that sodium reacts with water, you can expect potassium, in the same family, to do so too.
Some families are exact columns of the table: the alkali metals are group 1, the halogens group 17 and the noble gases group 18. Others, such as the metalloids, cut across several columns. Reference books draw some family borders differently. This site follows the grouping used by PubChem.
Metals, nonmetals and metalloids
About three quarters of all elements are metals: shiny, bendable, good carriers of heat and electricity. They fill six of the ten families here. Nonmetals, halogens and noble gases are all nonmetals in the wide sense. Metalloids lie between the two.
How to find a family on the table
Start at the edges. The far left column, leaving out hydrogen at the top, is the alkali metals, and the column next to it the alkaline earth metals. The far right column is the noble gases, and the column just before it the halogens. The wide block in the middle, ten columns across, is the transition metals. To their right lies a small triangle of post-transition metals, then a diagonal staircase of metalloids, and above and to the right of the staircase the nonmetals. The two rows printed below the main table are the lanthanides and the actinides. They belong inside the main table, after barium and radium, and are pulled out only so that the table fits on a page.
Families, groups and periods
These three words are easy to mix up. A group is a column of the table, numbered 1 to 18. A period is a row, numbered 1 to 7. A family is a set of elements that behave alike. Some families are exactly one group, but a family can also be a block of several groups or a diagonal band. Open any family to see its members side by side, with the trends in melting point and density worked out from the data.