An element is a pure chemical substance comprised of the same type of atom. Gold, for example, is an element and can be found in the periodic table. The periodic table of elements is an important reference for scientists and laymen alike. It organizes all the known elements in an informative array. Based on their general physical and chemical properties, elements are classified either as metals or nonmetals. Metals are located on the left side of the periodic table, and nonmetals are on the right. Metalloids form the intermediary boundary between the metal group and the nonmetal group. As such, metals and nonmetals have opposite properties, and the stark contrast between the two groups makes it possible to differentiate them from one another.
PHYSICAL PROPERTIES OF METALS
Metals differ physically from nonmetals. For one, metals are known for their luster; that is, they shine. Metals can also be stretched into wires, which is a physical property called ductility. Accordingly, metals are malleable, so they can be beaten into thin sheets. When viewed as a thin sheet, metals are opaque, and light cannot pass through them. Then, too, metals are known for being sonorous. In other words, they ring when struck. Plus, when it comes to strong attraction to a permanent magnet, three metals respond: cobalt, iron, and nickel. Meanwhile, the majority of metals take on the solid state when at room temperature. The exception, of course, is mercury. But perhaps the more notable physical characteristics of metals are their high densities, high melting points, and high conductivities. Testing for all the above physical properties can help determine if a substance is a metal.
PHYSICAL PROPERTIES OF NONMETALS
Once metals and metalloids are removed from the periodic table, the seventeen elements left comprise the nonmetal group. In contrast to metals, nonmetals are dull in appearance. They are nonductile and brittle. Interestingly enough, they tend to be transparent when viewed as a thin sheet. And, when hit, nonmetals make a dull sound. As for strong attraction to a permanent magnet, they have none. Curiously, at room temperature, about half of nonmetals are solids, the other half are gases, and one--namely, bromine--is a liquid. Moreover, nonmetals have comparatively lower densities and lower melting points. As opposed to metals, nonmetals, apart from carbon, are insulators. Carbon, however, comes in more than one form, which are termed allotropes. Allotropes of carbon include charcoal, graphite, and diamond. Graphite, the most stable form of carbon, has been found to exhibit metalloid properties, for it is a conductor. Diamond, nevertheless, is not a conductor.
CHEMICAL PROPERTIES OF METALS
Chemical properties can only be observed by changing the compositional identity of a substance, which usually involves a chemical reaction, such as flammability, corrosion, and reactivity to various agents. Chemically, metals differ from nonmetals in that they form positive ions, called cations. This occurs because metals are characterized by having one to three electrons in their outer shell, which tends to make them lose these valence electrons easily. To put it another way, metals undergoing chemical reaction lose electrons, which transforms them into positive ions, or cations. Because metals form positive ions they are known as electropositive elements, which makes them good reducing agents. Yet another chemical property of metals is that they form oxides that are more basic in pH. Finally, a great many metals undergo corrosion, evidenced by the iron nail that easily rusts, the silverware that tarnishes, and the Statue of Liberty’s copper developing verdigris patina.
CHEMICAL PROPERTIES OF NONMETALS
By contrast, nonmetals have four to eight electrons in their outer shell, allowing them to gain or share electrons. They form negative ions, called anions. Naturally, there are exceptions. Hydrogen, for example, can act as either a positive ion or a negative ion, depending on the situation. Then there are the noble gas atoms with electrons shells completely filled; this makes them relatively inert. Meanwhile, nonmetals in general are more electronegative. The oxides they form are more acidic in pH, consequently making nonmetals the preferred oxidizing agents. Interestingly, nonmetals tend to oxidize metals. Moreover, nonmetals do not corrode as easily as metals do. Finally, nonmetals are prone to form covalent bonds, unlike metals which can form ionic, metallic, and at times covalent bonds. A nonmetal element that illustrates covalent bond formation is carbon.