Gold

Gold - Au

CAS: 7440-57-5
Description:Soft, bright, yellow metal
Classification: Transition Metal
Date of Discovery: c. 3000 BC
Discoverer: Unknown
Name Origin: Old English geolo, "yellow"
Symbol Origin: Latin aurum, "gold"

Atomic Number: 79
Number of Neutrons: 118
Atomic Mass: 196.96654(3) amu
Melting Point: 1064.18 °C
Boiling Point: 2856 °C
Density (293 K):

19.3 g/cm³
Atomic volume: 10.2 cm³/mol
Electrical resistivity: 0.452 10^-6/cm

Thermal conductivity: 3.17 W/cmK
Enthalpy of atomization: 364 kJ/mol (est.)
Enthalpy of vaporization: 324.40 kJ/mol
Enthalpy of fusion: 12.550
Specific heat capacity: 0.128 J/gK

Energy levels: 2-8-18-32-18-1
Electron configuration: [Xe]4f¹⁴5d¹⁰6s¹
Crystal Structure: Cubic face centered
Atomic radius: 1.79 Å
Covalent radius: 1.34 Å
Oxidation States: +1, +3
Electronegativity, Pauling: 2.54
Electron affinity: 2.30863 eV
First ionization energy: 9.225 eV
2nd ionization energy: 20.521 eV
3rd ionization energy:
Polarizability: 5.8 10^-24cm³

Isotope	Natural Abundance	Atomic Mass	Half-life	Decay Mode	Spin
¹⁷²Au	4 ms
¹⁷³Au	172.9864	0.06 s
¹⁷⁴Au	173.9842	0.12 s
¹⁷⁵Au	174.9817	0.20 s
¹⁷⁶Au	175.9803	1.2 s	⁺, EC;
¹⁷⁷Au	176.9772	1.2 s
¹⁷⁸Au	177.9760	2.6 s
¹⁷⁹Au	178.9732	7.5 s
¹⁸⁰Au	179.9724	8.1 s	EC;
¹⁸¹Au	180.9700	11.4 s	EC;
¹⁸²Au	181.9686	21 s	⁺, EC;
¹⁸³Au	182.9676	42 s	EC;
¹⁸⁴Au	183.9675	53 s	EC, ⁺;	(5+)
^185mAu	6.8 m	⁺, EC; IT
¹⁸⁵Au	184.9657	4.3 m	⁺, EC;	(5/2-)
¹⁸⁶Au	< 2 m	⁺, EC
¹⁸⁶Au	185.9659	10.7 m	⁺, EC;	3-
^187mAu	2.3 s	IT	9/2-
¹⁸⁷Au	186.9646	8.3 m	⁺, EC	1/2+
¹⁸⁸Au	187.9651	8.8 m	⁺, EC	(1-)
^189mAu	4.6 m	⁺, EC	11/2-
¹⁸⁹Au	188.9642	28.7 m	EC; ⁺	1/2+
¹⁹⁰Au	189.96470	43 m	⁺; EC	1-
^191mAu	0.9 s	IT	11/2-
¹⁹¹Au	190.96365	3.2 h	EC	3/2+
¹⁹²Au	191.96481	4.9 h	⁺; EC	1-
^193mAu	3.9 s	IT	11/2-
¹⁹³Au	192.96413	17.6 h	EC	3/2+
¹⁹⁴Au	193.96534	1.64 d	⁺; EC	1-
^195mAu	30.5 s	IT	11/2-
¹⁹⁵Au	194.965017	186.12 d	EC	3/2+
^196m2Au	9.7 h	IT	12-
^196m1Au	8.1 s	IT	8+
¹⁹⁶Au	195.966551	6.18 d	EC	2-
^197mAu	7.8 s	IT; ^-	11/2-
¹⁹⁷Au	100.	196.966551	Stable	3/2+
^198mAu	2.30 d	IT	(12-)
¹⁹⁸Au	197.968225	2.694 d	^-	2-
¹⁹⁹Au	198.968748	3.14 d	^-	3/2+
^200mAu	18.7 h	^-; IT	12-
²⁰⁰Au	199.97072	48.4 m	^-	1-
²⁰¹Au	200.97165	26 m	^-	3/2+
²⁰²Au	201.9738	29 s	^-	(1-)
²⁰³Au	202.97515	1.0 m	^-	3/2+
²⁰⁴Au	203.9783	40 s	^-	(2-)
²⁰⁵Au	31 s	^-
Known and highly valued from earliest times, gold is found in nature as the free metal and in tellurides; it is very widely distributed and is almost always associated with quartz or pyrite. It occurs in veins and alluvial deposits, and is often separated from rocks and other minerals by sluicing and panning operations. About two-thirds of the world's gold output comes from South Africa, and about two thirds of the total U.S. production comes from South Dakota and Nevada. The metal is recovered from its ores by cyaniding, amalgamating, and smelting processes. Refining is also frequently done by electrolysis. Gold occurs in sea water to the extent of 0.1 to 2 mg/ton, depending on the location where the sample is taken. As yet, no method has been found for recovering gold from sea water profitably. It is estimated that all the gold in the world, so far refined, could be placed in a single cube 60 ft on a side. Of all the elements, gold in its pure state is undoubtedly the most beautiful. It is metallic, having a yellow color when in a mass, but when finely divided it may be black, ruby, or purple. The Purple of Cassius is a delicate test for auric gold. It is the most malleable and ductile metal; 1 oz. of gold can be beaten out to 300 ft². It's a soft metal and is usually alloyed to give it more strength. It is a good conductor of heat and electricity, and is unaffected by air and most reagents. It is used in coinage and is a standard for monetary systems in many countries. It is also extensively used for jewelry, decoration. dental work, and for plating. It is used for coating certain space satellites, as it is a good reflector of infrared and is inert. Gold, like other precious metals, is measured in troy weight; when alloyed with other metals, the term carat is used to express the amount of gold present, 24 carats being pure gold. For many years the value of gold was set by the U.S. at $20.67/troy ounce; in 1934 this value was fixed by law at $35.00/troy ounce, 9/10th fine. On March 17, 1968, because of a gold crisis, a two-tiered pricing system was established whereby gold was still used to settle international accounts at the old $35.00/troy ounce price while the price of gold on the private market would be allowed to fluctuate. Since this time, the price of gold on the free market has fluctuated widely. The price of gold on the free market reached a price of $620/troy oz. in January 1980. The most common gold compounds are auric chloride (AuCl₃) and chlorauric acid (HAuCl₄), the latter being used in photography for toning the silver image. Gold has forty six recognized isotopes and isomers; ¹⁹⁸Au, with a half-life of 2.7 days, is used for treating cancer and other diseases. Disodium aurothiomalate is administered intramuscularly as a treatment for arthritis. A mixture of one part nitric acid with three of hydrochloric acid is called aqua regia (because it dissolved gold, the King of Metals). Gold is available commercially with a purity of 99.999+%. For many years the temperature assigned to the freezing point of gold has been 1063.0 °C; this has served as a calibration point for the International Temperature Scales (ITS-27 and ITS-48) and the International Practical Temperature Scale (IPTS-48). In 1968, a new International Practical Temperature Scale (IPTS-68) was adopted, which demanded that the freezing point of gold be changed to 1064.43 deg C. In 1990 a new International Temperature Scale (ITS-90) was adopted bringing the t.p. (triple point) of H₂O (t₉₀ (°C)) to 0.01 deg C and the freezing point of gold to 1064.18 °C.The specific gravity of gold has been found to vary considerably depending on temperature, how the metal is precipitated, and cold-worked. LINKS: Gold Chemistry Gold Treatment Native Gold Return Sources for the information on this website include: Lide, David R., ed. CRC Handbook of Chemistry and Physics, 78th Ed., 1997-1998.

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