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.