- Any of a large group of chemical elements, including iron, gold, copper, lead, and magnesium, that readily become cations and form ionic bonds, having relatively free valence electrons (electrons in the outer shells). Metals are generally good conductors of electricity because of the freedom of their valence electrons. Metals generally conduct heat well, and in solid form are relatively malleable and ductile compared to other solids. They are usually shiny and opaque. All metals except mercury are solid at room temperature.
- An alloy, such as steel or bronze, made of two or more metals.
- In astronomy, any atom except hydrogen and helium.
- Small stones or gravel, mixed with tar to form tarmac for the surfacing of roads.
Usage Most metallic elements are lustrous or colorful solids that are good conductors of heat and electricity, and readily form ionic bonds with other elements. Many of their properties are due to the fact that their outermost electrons, called valence electrons, are not tightly bound to the nucleus. For instance, most metals form ionic bonds easily because they readily give up valence electrons to other atoms, thereby becoming positive ions (cations). The electrical conductivity of metals also stems from the relative freedom of valence electrons. In a substance composed of metals, the atoms are in a virtual ”sea“ of valence electrons that readily jump from atom to atom in the presence of an electric potential, creating electric current. With the exception of hydrogen, which behaves like a metal only at very high pressures, the elements that appear in the left-hand column of the Periodic Table are called alkali metals. Alkali metals, such as sodium and potassium, have only one electron in their outermost shell, and are chemically very reactive. (Hydrogen is exceptional in that, although it is highly reactive, its other metallic properties are manifest only at very high pressures.) Metals farther toward the right side of the Periodic Table, such as tin and lead, have more electrons in their outermost shell, and are not as reactive. The somewhat reactive elements that fall between the two extremes are the transition elements, such as iron, copper, tungsten, and silver. In most atoms, inner electron shells must be maximally occupied by electrons before an outer shell will accept electrons, but many transition elements have electron gaps in the shell just inside the valence shell. This configuration leads to a wide variety of available energy levels for electrons to move about in, so in the presence of electromagnetic radiation such as light, a variety of frequencies are readily emitted or absorbed. Thus transition metals tend to be very colorful, and each contributes different colors to different compounds.