Properties of metals, metalloids and nonmetals

The chemical elements can be broadly divided into metals, metalloids, and nonmetals according to their shared physical and chemical properties. All elemental metals have a shiny appearance (at least when freshly polished); are good conductors of heat and electricity; form alloys with other metallic elements; and have at least one basic oxide. Metalloids are metallic-looking, often brittle solids that are either semiconductors or exist in semiconducting forms, and have amphoteric or weakly acidic oxides. Typical elemental nonmetals have a dull, coloured or colourless appearance; are often brittle when solid; are poor conductors of heat and electricity; and have acidic oxides. Most or some elements in each category share a range of other properties; a few elements have properties that are either anomalous given their category, or otherwise extraordinary.
Elemental metals appear lustrous (beneath any patina); form compounds (alloys) when combined with other elements; tend to lose or share electrons when they react with other substances; and each forms at least one predominantly basic oxide.
Most metals are silvery looking, high density, relatively soft and easily deformed solids with good electrical and thermal conductivity, closely packed structures, low ionisation energies and electronegativities, and are found naturally in combined states.
Some metals appear coloured (Cu, Cs, Au), have low densities (e.g. Be, Al) or very high melting points (e.g. W, Nb), are liquids at or near room temperature (e.g. Hg, Ga), are brittle (e.g. Os, Bi), not easily machined (e.g. Ti, Re), or are noble (hard to oxidise, e.g. Au, Pt), or have nonmetallic structures (Mn and Ga are structurally analogous to, respectively, white P and I).
Metals comprise the large majority of the elements, and can be subdivided into several different categories. From left to right in the periodic table, these categories include the highly reactive alkali metals; the less-reactive alkaline earth metals, lanthanides, and radioactive actinides; the archetypal transition metals; and the physically and chemically weak post-transition metals. Specialized subcategories such as the refractory metals and the noble metals also exist.
Metalloids are metallic-looking often brittle solids; tend to share electrons when they react with other substances; have weakly acidic or amphoteric oxides; and are usually found naturally in combined states.
Most are semiconductors, and moderate thermal conductors, and have structures that are more open than those of most metals.
Some metalloids (As, Sb) conduct electricity like metals.
The metalloids, as the smallest major category of elements, are not subdivided further.
Nonmetallic elements often have open structures; tend to gain or share electrons when they react with other substances; and do not form distinctly basic oxides.
Most are gases at room temperature; have relatively low densities; are poor electrical and thermal conductors; have relatively high ionisation energies and electronegativities; form acidic oxides; and are found naturally in uncombined states in large amounts.
Some nonmetals (black P, S, and Se) are brittle solids at room temperature (although each of these also have malleable, pliable or ductile allotropes).
From left to right in the periodic table, the nonmetals can be divided into the reactive nonmetals and the noble gases. The reactive nonmetals near the metalloids show some incipient metallic character, such as the metallic appearance of graphite, black phosphorus, selenium and iodine. The noble gases are almost completely inert.
The characteristic properties of elemental metals and nonmetals are quite distinct, as shown in the table below. Metalloids, straddling the metal-nonmetal border, are mostly distinct from either, but in a few properties resemble one or the other, as shown in the shading of the metalloid column below and summarized in the small table at the top of this section.
Authors differ in where they divide metals from nonmetals and in whether they recognize an intermediate metalloid category. Some authors count metalloids as nonmetals with weakly nonmetallic properties. Others count some of the metalloids as post-transition metals.
Within each category, elements can be found with one or two properties very different from the expected norm, or that are otherwise notable.
Sodium, potassium, rubidium, caesium, barium, platinum, gold
Manganese
Iron, cobalt, nickel, gadolinium, terbium, dysprosium, holmium, erbium, thulium
Iridium
Gold
Mercury
Lead
Bismuth
Uranium
Plutonium
Boron
Boron, antimony
Silicon
Arsenic
Antimony
Hydrogen
Helium
Carbon
Phosphorus
Iodine