Characterizing the Elements
Elements can generally be described as either metals or nonmetals. Metal elements are usually good conductors of both electricity and heat. The dividing line between metals and non-metals is not hard and fast, thus the distinction between "Post-transition metals" and "Metalloids" is represented differently on different versions of the Periodic Table. For example, in some tables, Group 12 is is categorized with the post-transition metals, and in others, aluminum and tin are included characterized as Metalloids or poor metals. In our version of the table, we have chosen the most commonly accepted demarcations between these elements.
- Alkali metals. The alkali metals make up group 1 of the Table, and comprise Li through Fr. They have very similar behavior and characteristics. Hydrogen is group 1 but exhibits few characteristics of a metal and is often categorized with the nonmetals.
- Alkaline earth metals. The alkaline earth metals make up group 2 of the periodic table, from Be through Ra. The alkaline earth metals have very high melting points and oxides that have basic alkaline solutions. Their characteristics are well described and consistent down the group.
- Transition metals. The transition elements are metals that have a partially filled d subshell (CRC Handbook of Chemistry and Physics) and comprise groups 3 through 12 and the lanthanides and actinides (see below).
- Post-transition metals. The post-transition elements are Al, Ga, In, Tl, Sn, Pb and Bi. As their name implies, they have some of the characteristics of the transition elements. They tend to be softer and conduct more poorly than the transition metals.
- Metalloid (or "semi-metal" or "poor metal"). The metalloids are B, Si, Ge, As, Sb, Te, and Po. They sometimes behave as semiconductors (B, Si, Ge) rather than as conductors.
- Lanthanides. The lanthanides comprise elements 57 (lanthanum, hence the name of the set) through 71. They are grouped together because they have similar chemical properties. They, along with the actinides, are often called "the f-elements" because they have valence electrons in the f shell.
- Actinides. The actinides comprise elements 89 through 103. They, along with the lanthanides, are often called "the f-elements" because they have valence electrons in the f shell. Only thorium and uranium are naturally occurring actinides with significant abundance. They are all radioactive.
- Nonmetals. The term "nonmetals" is used to classify the elements H, C, N, P, O, S, and Se.
- Halogens. The halogen elements are a subset of the nonmetals. They comprise group 17 of the periodic table, from F through At. They generally very chemically reactive and are present in the environment as compounds rather than as pure elements.
- Noble gases. The noble gases comprise group 18. They are generally very stable chemically and exhibit similar properties of being colorless and odorless.
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