Nobelium, Zirconium, and Cobalt

I. The History of Cobalt

A. Used in Ancient Times to make glass a rich blue color by way of compounds

1. The word is generally accepted as derived from the Greek by way of medieval German.

a) Records of the name only go back to 1335 when it was applied to gnomes living in the mines in the Schneeberg Mountains in Germany.

2. Cobalt coloring of ceramics has been known for well over 2,000 years in Persia and Egypt. So it probably went by another unknown name.

B. Discovered in 1735 by George Brandt

1. He was able to show that cobalt was the source of the blue color in glasses, which previously had been attributed to the bismuth found with cobalt.

2. The word cobalt comes from the German kobalt or kobold, meaning evil spirit, the metal being so called by miners, because it is poisonous. Other sources cite the origin as stemming from silver miners' belief that cobalt had been placed by kobolds who had stolen the silver. Some also think the name may derive from Greek kobalos, which means 'mine', and which may have common roots with kobold, goblin, and cobalt.

II. Properties of Cobalt

A. Physical Properties

a) Melting point - 1768 K (1495 °C, 2723 °F)

b) Boiling point - 3200 K (2927 °C, 5301 °F)

c) Density - 8.90 g/cmі - Liquid density at m.p. 7.75 g/cmі

d) Atomic Number 27 - Symbol Co - Atomic Weight 58.9332

e) Electron Configuration [Ar]4s23d7

f) Cobalt is a hard, brittle metal. It is similar in appearance to iron and nickel

B. Chemical Properties

a) Pure cobalt does not dissolve in water but is soluble in acids

b) It is incompatible or reactive with acetylene, hydrazinium nitrate, ammonium nitrate, and oxidants

c) It is a moderate fire hazard when exposed to heat or flame or by spontaneous chemical reaction.

d) Natural cobalt can stay in the air for a few days, but it will stay for years in water and soil.

III. Uses for Cobalt

A. Applications

a) Alloys

b) Magnets and magnetic recording media

c) Drying agents for paints, varnishes, and inks.

d) Pigments (cobalt blue and cobalt green) - paint

e) Cobalt-60 has multiple uses as a gamma ray source

f) Battery electrodes.

g) Radiotherapy

B. Uses

c) It is alloyed with iron, nickel, and other metals to form Alnico, an alloy with magnetic strength.

b) Cobalt, chromium, and tungsten may be alloyed to form Stellite, which is used for high-temperature, high-speed cutting tools and dyes.

c) Cobalt is used in magnet steels and stainless steels. It is used in electroplating because of its hardness and resistance to oxidation.

d)Cobalt salts are used to impart permanent brilliant blue colors to glass, pottery, enamels, tiles, and porcelain. A cobalt chloride solution is used to make a sympathetic ink.

C. Isotopes

a) Naturally occurring cobalt is composed of 1 stable isotope, Co-59

b) Most stable being

1) Co-60 with a half-life of 5.2714 years

2) Co-57 with a half-life of 271.79 days

3) Co-56 with a half-life of 77.27 days

4) C0-58 with a half life of 70.86 days

5) All of the remaining radioactive isotopes have half-lifes that are less than 18 hours and the majority of these have half lives that are less than 1 second.

IV. Isolation of Cobalt

A. It is not normally necessary to make cobalt in the laboratory as it is available readily commercially. Many ores contain cobalt.