Elements with the same classification often have similar properties. These elements are organized in the periodic table into three main categories: metals, metalloids, and nonmetals.
A metal is one of a class of elements that tend to have a metallic luster (partly reflective), be good conductors of electricity and thermal energy, and be malleable (able to be reshaped and reformed without breaking) and ductile (able to be drawn into thin wire). Metals are used to make coins, for example, because they are malleable, which means they can be formed into various shapes without breaking. The shininess of a metal coin is its luster. Copper can be drawn into a thin wire because it is ductile. All metals except for mercury are solids at room temperature.
Metals generally have a low ionization energy, which is the amount of energy required to remove an electron from an atom. Consequently metals tend to form cations (positively charged ions) in solution. Because of their low ionization energy, metals are easily oxidized, which means they easily lose electrons. Metals also have a low electronegativity (attraction for electrons when forming bonds) compared to nonmetals. As a result, compounds consisting of a metal and a nonmetal tend to form ionic bonds, which is when one atom (the metal) gives up one or more electrons to another atom (the nonmetal). Due to the abundance of oxygen on Earth, metal oxides commonly form in nature when a metal reacts with oxygen. Metal oxides tend to be ionic and commonly form basic solutions when they dissolve in water.
A nonmetal is one of a class of elements that tend to not have metallic luster, be poor conductors of electricity and thermal energy, and be neither malleable nor ductile. Nonmetals can be solids, liquids, or gases at room temperature. Nonmetals that are solid at room temperature are brittle, which means they break under stress.
Nonmetals have a higher ionization energy than metals because they have a smaller atomic radius, which is defined as half the distance between the nuclei of two identical atoms. Because nonmetals have a greater electronegativity than metals, they generally gain electrons when reacting with metals. Compounds that are made up of two nonmetals are molecular compounds. Many such compounds, such as ammonia (NH3) and methane (CH4), are gases at room temperature. Some nonmetal molecular compounds are liquids, and a few are solid at room temperature.
An important type of nonmetals is nonmetal oxides, which form when a nonmetal bonds with oxygen. Oxygen is a nonmetal, and like other nonmetal-nonmetal compounds, nonmetal oxides are mostly molecular in character. Nonmetal oxides are commonly acidic and in solution they generally form anions (negatively charged ions) or oxyanions (anions with oxygen atoms bonded to another element).
A metalloid is one of a class of elements that tend to have properties of both metals and nonmetals. For example, metalloids poorly conduct electricity when compared to metals but are better conductors of electricity than nonmetals. Some metalloids are semiconductors, which means their electrical conductivity can be changed by adding small amounts of certain other substances. When used as semiconductors, metalloids can be used in electronic circuitry because their electrical conductivity can be easily controlled.Pure metals contain only one type of metallic element and are held together by metallic bonds. Metallic ions are most often cations. Pure nonmetals form molecules. Ions of nonmetals are often anions. Some metalloid solids are molecular, like nonmetals.