Among metals, pure silver has the highest thermal conductivity (thenonmetal diamond and superfluid helium II are higher) and one of the highest optical reflectivities. (Aluminium slightly outdoes silver in parts of the visible spectrum, and silver is a poor reflector of ultraviolet). Silver also has the lowest contact resistance of any metal. Silver halides are photosensitive and are remarkable for their ability to record a latent image that can later bedeveloped chemically. Silver is stable in pure air and water, but tarnishes when it is exposed to air or water containing ozone or hydrogen sulfide, the latter forming a black layer of silver sulfide which can be cleaned off with dilute hydrochloric acid. The most common oxidation state of silver is +1 (for example, silver nitrate, AgNO3); however, the less common +2 compounds (for example,silver(II) fluoride, AgF2), and the even less common +3 (for example, potassium tetrafluoroargentate, KAgF4) and even +4 compounds (for example, potassium hexafluoroargentate, K2AgF6) are also known.
Main article: Isotopes of silver
Naturally occurring silver is composed of two stable isotopes, 107Ag and 109Ag, with 107Ag being slightly more abundant (51.839% natural abundance). Silver'sisotopes are almost equal in abundance, something which is rare in the periodic table. Silver's atomic weight is 107.8682(2) g/mol. Twenty-eight radioisotopes have been characterized, the most stable being 105Ag with a half-life of 41.29 days, 111Ag with a half-life of 7.45 days, and 112Ag with a half-life of 3.13 hours. This element has numerous meta states, the most stable being 108mAg(t1/2 = 418 years), 110mAg (t1/2 = 249.79 days) and 106mAg (t1/2 = 8.28 days). All of the remaining radioactive isotopes have half-lives that are less than an hour, and the majority of these have half-lives that are less than three minutes.
Isotopes of silver range in relative atomic mass from 93.943 (94Ag) to 126.936 (127Ag); the primary decay mode before the most abundant stable isotope,107Ag, is electron capture and the primary mode after is beta decay. The primary decay products before 107Ag are palladium (element 46) isotopes, and the primary products after are cadmium (element 48) isotopes.
The palladium isotope 107Pd decays by beta emission to 107Ag with a half-life of 6.5 million years. Iron meteorites are the only objects with a high-enough palladium-to-silver ratio toyield measurable variations in 107Ag abundance. Radiogenic 107Ag was first discovered in the Santa Clara meteorite in 1978. The discoverers suggest the coalescence and differentiation of iron-cored small planets may have occurred 10 million years after a nucleosynthetic event. 107Pd–107Ag correlations observed in bodies that have clearly been melted since the accretion of the solar system mustreflect the presence of unstable nuclides in the early solar system.
Silver metal dissolves readily in nitric acid (HNO3) to produce silver nitrate (AgNO3), a transparent crystalline solid that is photosensitive and readily soluble in water. Silver nitrate is used as the starting point for the synthesis of many other silver compounds, as an antiseptic, and as a yellow stain for...