A metalloid is a chemical element with properties that are intermediate between those of metals and nonmetals. The following elements are generally classified as metalloids:: Boron, silicon, germanium, arsenic, antimony, tellurium, and polonium. (There is some debate about whether or not to classify polonium as a metalloid. Because very limited amounts of this element have been available, its properties have been difficult to study.)
The term metalloid is derived from the Greek words metallon, meaning "metal," and eidos, meaning "sort."
In the standard layout of the periodic table, metalloids occur along a diagonal line through the p block, from boron to polonium. Elements to the upper right of this line display increasing nonmetallic behavior; elements to the lower left display increasing metallic behavior. This line is called the "stair-step" or "staircase." The poor metals are to the left and down, and the nonmetals are to the right and up.
Listed in order of increasing atomic number, the metalloids are:
Their positions in the periodic table are shown in the chart below.
As noted above, the properties of metalloids are intermediate between those of metals and nonmetals. For instance, arsenic and antimony are crystalline solids that look like metals, but in chemical reactions, they behave as either metals or nonmetals.
The oxides of metalloids are usually amphoteric. By comparison, metals generally form basic oxides, and nonmetals tend to form acidic oxides. Also, several metalloids (particularly boron, silicon, and germanium) behave as semiconductors, implying that they can carry an electric charge under certain conditions. In addition, the electronegativity and ionization energy values for the metalloids lie between those of the metals and nonmetals.
The chemical reactivity of a metalloid depends on the substance with which it is reacting. For example, boron behaves as a nonmetal when reacting with sodium, but it acts as a metal when reacting with fluorine.
Most metalloids can exist in the form of several allotropes. For a given metalloid, one allotrope may behave as a metal while another may behave as a nonmetal.
For the element carbon (classified as a nonmetal), its diamond allotrope is clearly nonmetallic, but the graphite allotrope displays limited electric conductivity, more characteristic of a metalloid. Also, some allotropes of phosphorus, tin, selenium, and bismuth have properties that are similar to metalloids.
The concepts of metalloid and semiconductor should not be confused with each other. Although some metalloids are semiconductors, not all semiconductors are metalloids. The term "metalloid" refers to the properties of certain elements of the periodic table. The term "semiconductor" refers to the physical properties of materials (including alloys and compounds). There is only partial overlap between the two.
|Standard table | Vertical table | Table with names | Names and atomic masses (large) | Names and atomic masses (small) | Names and atomic masses (text only) | Inline F-block | Elements to 218 | Electron configurations | Metals and non metals | Table by blocks | List of elements by name|
|Groups: 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12 - 13 - 14 - 15 - 16 - 17 - 18|
|Periods: 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8|
|Series: Alkalis - Alkaline earths - Lanthanides - Actinides - Transition metals - Poor metals - Metalloids - Nonmetals - Halogens - Noble gases|
|Blocks: s-block - p-block - d-block - f-block - g-block|
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