Indium (49)

Indium is a very soft, silvery-white metal with a brilliant luster. The pure metal gives a high-pitched "scream" when bent. It wets glass, as does gallium. It is useful for making low-melting alloys. An alloy of 24% indium and 76% gallium is liquid at room temperature. Canada produces the majority of the world's supply of indium.

•Name: Indium
•Symbol: In
•Atomic number: 49
•Atomic weight: 114.818 (3)
•Standard state: solid at 298 K
•CAS Registry ID: 7440-74-6
•Group in periodic table: 13
•Period in periodic table: 5
•Block in periodic table: p-block
•Color: silvery lustrous grey
•Classification: Metallic

Historical information

Indium was discovered by Ferdinand Reich, Hieronymus Theodor Richter at 1863 in Germany. Origin of name is from the indigo line in its atomic spectrum. Indium was discovered by Ferdinand Reich and Theodore Richter, who later isolated the metal. It was found and spectroscopically identified as a minor component in zinc ores. Until 1924, a gram or so constituted the world's supply of this element in isolated form. In fact, it is probably about as abundant as silver.

Physical properties

•Melting point: 429.75 [or 156.6 °C (313.88 °F)] K
•Boiling point: 2345 [or 2072 °C (3762 °F)] K
•Density of solid: 7310 kg m-3

Orbital properties

•Ground state electron configuration: [Kr].4d10.5s2.5p1
•Shell structure: 2.8.18.18.3
•Term symbol: 2P1/2

 

Isolation

Indium would not normally be made in the laboratory as it is commercially available. Indium is a byproduct of the formation of lead and zinc. Indium metal is isolated by the electrolysis of indium salts in water. Further processes are required to make very pure indium for electronics purposes.

Cadmium (48)

Cadmium is a soft, bluish-white metal and is easily cut with a knife. It is similar in many respects to zinc. Interestingly, a characteristic cadmium "scream" is heard on bending a cadmium bar (better than the lambs!). Cadmium and its compounds are highly toxic. Silver solder, which contains cadmium, should be handled with care (this along with lead makes it a health hazard concern).

•Name: Cadmium
•Symbol: Cd
•Atomic number: 48
•Atomic weight: 112.411
•Standard state: solid at 298 K
•CAS Registry ID: 7440-43-9
•Group in periodic table: 12
•Period in periodic table: 5
•Block in periodic table: d-block
•Color: silvery grey metallic
•Classification: Metallic

Historical information

Cadmium was discovered by Friedrich Strohmeyer at 1817 in Germany. Origin of name is somewhat confusing, from the Latin word "cadmia" meaning "calamine" (zinc carbonate, ZnCO3) and from the Greek word "kadmeia" with the same meaning. Cadmium was discovered by Friedrich Stromeyer in 1817 from an impurity in some samples of zinc carbonate, ZnCO3. He noted that these particular samples changed color on heating, which pure zinc carbonate does not. He was persistent enough to follow this observation through and he eventually isolated some cadmium metal by roasting and reduction of the sulfide.

Physical properties

•Melting point: 594.22 [or 321.07 °C (609.93 °F)] K
•Boiling point: 1040 [or 767 °C (1413 °F)] K
•Density of solid: 8650 kg m-3

Orbital properties

•Ground state electron configuration: [Kr].4d10.5s2
•Shell structure: 2.8.18.18.2
•Term symbol: 1S0

Isolation

It is rare that preparation of cadmium in the laboratory should be required because of environmental concerns about cadmium. The isolation of cadmium is associated with zinc recovery as cadmium is an impurity in zinc ores. Most zinc production is based upon sulfide ores. These are roasted in industrial plants to form zinc oxide, ZnO. This may be reduced with carbon to form zinc metal, but in practice ingenious technology is required to ensure that the resulting zinc does not contain oxide impurities.

ZnO + C → Zn + CO

ZnO + CO → Zn + CO2

CO2 + C → 2CO

After this process, zinc may be refined by distillation under vacuum and this process also allows the separation of any cadmium present in the crude zinc.

The other type of extraction of zinc is electrolytic. Dissolution of crude zinc oxide, ZnO, in sulphuric acid gives zinc sulphate, ZnSO4 in solution. Before electrolysis to produce zinc, the cadmium impurity and is removed as a precipitate by the addition of zinc dust as cadmium sulphate

Silver (47)

June 3^rd:
SILVER (47)

Silver is somewhat rare and expensive, although not as expensive as gold. Slag dumps in Asia Minor and on islands in the Aegean Sea indicate that man learned to separate silver from lead as early as 3000 B.C. Pure silver has a brilliant white metallic luster. It is a little harder than gold and is very ductile and malleable. Pure silver has the highest electric...al and thermal conductivity of all metals, and possesses the lowest contact resistance. Silver iodide, AgI, is (or was?) used for causing clouds to produce rain.

Silver is stable in pure air and water, but tarnishes when exposed to ozone, hydrogen sulfide, or air containing sulphur. It occurs in ores including argentite, lead, lead-zinc, copper and gold found in Mexico, Peru, and the USA.

•Name: Silver
•Symbol: Ag
•Atomic number: 47
•Atomic weight: 107.8682
•Standard state: solid at 298 K
•CAS Registry ID: 7440-22-4
•Group in periodic table: 11
•Group name: Coinage metal
•Period in periodic table: 5
•Block in periodic table: d-block
•Color: silver
•Classification: Metallic

Historical information

Silver was discovered by Known since ancient times at no data in not known. Origin of name is from the Anglo-Saxon word "siolfur" meaning "silver" (the origin of the symbol Ag comes from the Latin word "argentum" meaning "silver"). Silver has been known since ancient times. It is mentioned in Genesis. Slag dumps in Asia Minor and on islands in the Aegean Sea indicate that man learned to separate silver from lead as early as 3000 B.C.

Silver is one of the elements which has an alchemical symbol, alchemy is an ancient pursuit concerned with, for instance, the transformation of other metals into gold.

Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions). This was further evidence for atoms. Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. The symbol used by Dalton for silver is a circle with an upper case S in the middle.

Physical properties

•Melting point: 1234.93 [or 961.78 °C (1763.2 °F)] K
•Boiling point: 2435 [or 2162 °C (3924 °F)] K
•Density of solid: 10490 kg m-3

Orbital properties

•Ground state electron configuration: [Kr].4d10.5s1
•Shell structure: 2.8.18.18.1
•Term symbol: 2S1/2

Isolation

Silver is readily available commercially so it is not normally necessary to prepare silver in the laboratory. However the formation of silver metal may be demonstrated in a satisfying reaction in which copper metal is dipped into a solution of silver nitrate, AgNO3.

Cu(s) + 2 AgNO3 (aq) → Cu(NO3)2 + 2 Ag (s)

The result is formation of often attractive silver crystals and a blue-green solution of copper nitrate. Industrially, silver is usually a byproduct of processes whose main object is the extraction of another metal such as copper, lead, and zinc. So called "anode slimes" from the electrolytic purification of copper contain silver and a somewhat involved process is finished by electrolysis of a nitrate solution containing silver.