Group 8 element

While groups (columns) of the periodic table are usually named after their lightest member (as in "the oxygen group" for group 16), iron group has historically been used differently; most often, it means a set of adjacent elements on period (row) 4 of the table that includes iron, such as chromium, manganese, iron, cobalt, and nickel, or only the last three, or some other set, depending on the context.

Like other groups, the members of this family show patterns in electron configuration, especially in the outermost shells, resulting in trends in chemical behavior.

Basic properties

^{The following is copied from the pages of Iron, Ruthenium, Osmium, and Hassium respectively.}

Pristine and smooth pure iron surfaces are a mirror-like silvery-gray. Iron reacts readily with oxygen and water to produce brown-to-black hydrated iron oxides, commonly known as rust. Unlike the oxides of some other metals that form passivating layers, rust occupies more volume than the metal and thus flakes off, exposing more fresh surfaces for corrosion. High-purity irons (e.g. electrolytic iron) are more resistant to corrosion.

Because it hardens platinum and palladium alloys, ruthenium is used in electrical contacts, where a thin film is sufficient to achieve the desired durability. With its similar properties to and lower cost than rhodium, electric contacts are a major use of ruthenium. The ruthenium plate is applied to the electrical contact and electrode base metal by electroplating or sputtering.

Osmium is a hard but brittle metal that remains lustrous even at high temperatures. It has a very low compressibility. Correspondingly, its bulk modulus is extremely high, reported between 395 and 462 GPa, which rivals that of diamond (443 GPa). The hardness of osmium is moderately high at 4 GPa. Because of its hardness, brittleness, low vapor pressure (the lowest of the platinum-group metals), and very high melting point (the fourth highest of all elements, after carbon, tungsten, and rhenium), solid osmium is difficult to machine, form, or work.

Very few properties of hassium or its compounds have been measured; this is due to its extremely limited and expensive production and the fact that hassium (and its parents) decays very quickly. A few singular chemistry-related properties have been measured, such as enthalpy of adsorption of hassium tetroxide, but properties of hassium metal remain unknown and only predictions are available. Though despite its radioactivity, chemists have formed hassium tetroxide and sodium hassate(VII) through various means.