Did You Know?► The chemical reactivity of a metalloid depends on the substance it reacts with. These elements behave like non-metals when reacting with metals. However, when reacting with non-metals, they exhibit chemical properties similar to those of metals.
The periodic table of elements was the brain child of Dmitri Ivanovich Mendeleev. He was a Russian chemist who proposed his version of the periodic table in 1864. Mendeleev found that several elements that shared similar properties, occurred at regular intervals on the periodic table. He sorted the elements on the periodic table into three major categories - metals, non-metals and metalloids. In this article, we shall learn more about metalloids and their properties.
Metalloids are those chemical elements that exhibit properties of both metals and non-metals. Since elements with similar properties are placed together in the periodic table, all metalloids are placed together between the metals and non-metals.
Metalloid is a term that is derived from the Latin word, metallum which means 'metal', and the Greek word oeides which means 'sort of'. There are seven metalloids, and they are placed in the groups 13, 14, 15, 16 and 17, in the p block of the periodic table. They are separated from the metals and non-metals by a zig-zag line, known as the 'amphoteric line'. Metalloids in the periodic table include Boron (B), Silicon (Si), Germanium (Ge), Arsenic (Ar), Antimony (Sb), and Tellurium (Te).
Here are the general physical properties exhibited by metalloids. Refer to the images inside the boxes, for the electronic configuration of each.
► Metalloids are solids at room temperature.
► They are lustrous i.e. they have a shiny surface like metals.
► Some of them are ductile in nature and can be drawn into pipes and wires.
► They are fair conductors of heat and electricity, but not as good as metals. Hence, they are also known as semi-conductors. Metalloids like boron, germanium, and arsenic are used as dopants in glasses for use in semiconductor chips.
► They are usually brittle in nature.
► These elements mostly exist in several allotropic forms.
► The density of metalloids is lower than that of poor metals, but higher than that of non-metals.
► The temperature coefficient of resistance can be positive (arsenic and antimony) or negative (boron, silicon, germanium, tellurium) for metalloids.
► They have an open crystal structure, as opposed to the closed crystal structure of metals.
► They have abnormally high values of enthalpy of fusion.
► They exhibit electrical conductivity even in the liquid form.
► In metalloids, fewer valence electrons are available as "free electrons".
Metalloids tend to have an intermediate property between metals and non-metals. Given below are some general chemical properties of metalloids.
► In a standard periodic table layout, you will observe that the metalloids that are placed on the upper right side of the diagonal line through the p-block, display increasing non-metallic behavior. However, those placed to the lower left of the line are more metallic in character. This diagonal line is called the 'stair-step' or 'staircase'.
► The general chemical behavior of metalloids is similar to that of non-metals.
► Many metalloids have multiple of oxidation states or valences. However, in most chemical reactions, they may behave either as metals or non-metals.
► The metalloids usually form amphoteric oxides. The oxides formed by metals are basic oxides, while non-metals generally form acidic oxides.
► The ionization energy of metalloids is higher than that of metals, but lower than that of non-metals.
► Many metalloids have different allotropes. For a given metalloid, one of its allotrope may react as a metal and the other allotrope may behave as a non-metal. For example, carbon in its diamond allotrope acts like a true non-metal and is a bad conductor of electricity, but its graphite allotrope is a fairly good electrical conductor.
► Allotropes of tin, phosphorous and bismuth exhibit borderline behavior.
► Metalloids form anions (negatively charged ions) in water.
► These elements can form ionic as well as covalent bonds.
► The oxidation number for metalloids can be positive or negative.
► Metalloids can react with metals to form alloys.
► The oxides of metalloids are weakly acidic. They are amorphous and when heated beyond a certain temperature, which is known as the glass transition temperature), form glass.
► The halides of metalloids are soluble in organic solvents.
► Metalloids form covalent hydrides that are volatile.
► Some metalloids (boron, silicon, arsenic, and selenium) can form organometallic compounds, which are compounds that contain covalent bonds between a metal and carbon atoms.
This was some basic information related to the properties of metalloids. Hope this article has helped you learn about this unique cluster of elements in the periodic table.