Gold Au (Element 79) of Periodic Table

79 Au (Gold)

Of all the elements, Apparence of pure gold (24 carat) is the most beautiful.
It is soft, metallic, having yellow colour, and when finely divided, it may be convert to black, ruby, or purple colour, where the Purple of Cassius is a delicate test for auric gold (Au³⁺).
It is the most ductile & malleable metal, even 28 gm (1 ounce) of gold can be beaten upto 300 square feet.

The metal is a good conductor of heat & electricity, and Also inert (unaffected by air and most reagents).

Due to its softness, It is usually alloyed to give it more strength.

The most common gold compounds are Chlorauric acid (HAuCl₄) & Auric chloride (AuCl₃).

It is Unreactive with air & most reagents, But It is dissolved in aqua regia (mixture of nitric & hydrochloric acid in ratio of 1:3).

Identity
CAS Number: CAS7440-57-5
CID Number: CID23985
RTECS Number: RTECSMD5070000

CONTENT INDEX

Basic Properties of Gold

Appearance: Metallic yellow
Mass Number: 197
Standard Atomic weight: 196.966 g/mol
Atomic number (Z): 79
Electrons: 79
Protons: 79
Neutrons: 118
Period: 6
Group: 11
Block: d
Element category: Transition metal
Electrons per shell: K2, L8, M18, N32, O18, P1
Electron configuration: 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰5s²5p⁶4f¹⁴5d¹⁰6s¹

Gold electron configuration — Gold Electron Configuration

Thermal Properties of Gold

Phase: Solid
Melting point: 1337.33 K (1064 ^oC, 1947.52 ^oF)
Boiling point: 3243 K (2970 ^oC, 5378 ^oF)
Debye temperature: 170 K (-103.15 ^oC, -153.67 ^oF)
Fusion heat: 12.55 kJ/mol
Vaporization heat: 342 kJ/mol
Specific heat: 129 J/(kg K)
Molar heat capacity: 25.418 J/(mol.K)
Thermal expansion: 14.2 μm/(m∙K)
Thermal conductivity: 318 W/(m∙K)

Electrical properties of Gold

Electrical conductivity: 45×10⁶ S/m
A Electrical resistivity: 22.14 nΩ∙m
A Electrical type: Conductor

Magnetic Properties of Gold

A Magnetic type: Diamagnetic
Magnetic susceptibility (x_mol): -28×10^-6 cm³/mol
Volume magnetic susceptibility: -0.0000344
Mass magnetic susceptibility: -1,78×10^-9 m³/kg
Molar magnetic susceptibility: -0.351×10^-9 m³/mol

Physical Properties of Gold

Density: 19.30 g/cm³ (In solid) 17.31 g/cm³ (In Liquid at M.P)
Molar volume: 0.00001021 m³/mol
Tensile strength: 120 MPa
Young’s modulus: 79 GPa
Shear modulus: 27 GPa
Mohs Hardness: 2.5
Bulk modulus: 180 GPa
Poisson ratio: 0.4
Vicker hardness: 188-216 MPa
Brinell hardness: 188-245 MPa
Sound Speed: 2030 m/s

Atomic Properties of Gold

Oxidation states: -3, -2, -1, 1, 2, 3, 5
Valence Electrons: 5d¹⁰ 6s¹
Ion charge: Au³⁺ Au⁺
Ionization potential of an atom: 9.19
Ionization energies: 1st: 890 kJ.mol 2nd: 1980 kJ/mol
Ionic radius: 85 pm
Atomic radius: 144 pm (empirical)
Van der Waals: 166 Pm
Covalent radius: 136±6 pm
Filling Orbital: 5d¹⁰
Crystal structure: Face centered cubic
Lattice angles: π/2, π/2, π/2
Lattice constant: 407.83, 407.83, 407.83 pm
Grid parameters: a=408 Å
Space Group Name: Fm_3m
Space Group Number: 225

Reactivity of Gold

Electronegativity: 2.54 (pauling scale)
Valence: +5
Electron affinity: 222.8 kJ/mol

Nuclear Properties of Gold

Half Life: Stable (Infinity)
Lifetime: Stable (Infinity)
Quantum Number: ²S_1/2
Neutron cross section (Brans): 98.7
Neutron Mass Absorption: 0.017
Isotopes: 195_Au 196_Au 197_Au 198_Au 199_Au

Isotope	Abundance (%)	Atomic Mass g/mol	Half Life (t_1/2)
195_Au	Syn	–	186.1 d
196_Au	Syn	–	6.183 d
197_Au	100	196.966	Stable
198_Au	Syn	197.967	2.695 d
199_Au	Syn	–	3.169 d

Chemical Reactions of Gold

The metal reacts chlorine & Bromine, and forming trihalides:
2 Au (s) + 3 Cl₂ (g) → 2 AuCl₃ (s)    (gold (III) chloride)
2 Au (s) + 3 Br₂ (g) → 2 AuBr₃ (s)   (gold (III) Bromide)
Reacts with iodine, It forms monohalide:
2 Au (s) + I₂ (g) → 2 AuI (s)   (gold (I) iodide)

Gold History

Naming: Au from Latin: aurum, meaning gold (from old English word geolo (yellow))
Discovery: (before 6000 BCE) In the Middle East

Gold Uses

Mostly Gold is used as bullion (used for trade on a market), however, it is also extensively used in Jewellery (in both Pure & alloy forms).
The purity of Gold is recognize by the term ‘Carat’, which indicates the amount of gold present in an alloy, where ‘24 carat’ is pure gold & it is very soft.

Mathematically,
1 carat is equals to 41.66 fineness,
24 carat gold equals to 999.99 fineness (Pure gold),
18 carat gold means 18 part of gold & 6 part of other metal (Gold alloy).

Gold alloys with 18 & 9 carat are commonly used , because they are more durable.
A Very thin sheets of gold (can be called as gold leaf) is used in art, for decoration, and as architectural ornament.

Gold is a good reflector of infrared, so it is used for coating certain space satellites, and on the windows of large building to reflect the heat of the Sun’s ray.

The metal is used in electroplating to cover another metal with a very thin layer of gold, which is used in cheap jewellery, gears of watches, artifitial limb joints, electrical connectors etc…

Because of its good conducting of electricity, it doesn’t corrode (break the contact), therefore, Gold electroplating is also used in electronic industry to protect their copper components & improve their solderability (used for joining), even the thin gold wires are used inside the computer chips to produce circuits.

In Medical field, the gold compounds is used to treat in some cases of arthritis, and The Dentists sometime use gold alloys for fillngs.

Gold nanoparticles are used as industrial catalyst, like Vinyl acetate (C₄H₆O₂), which is used to make PVA (for glue, paint and resin).

Biological role of Gold: It is Non-toxic.

Abundance of Gold

Gold is one of the few elements to occur in a natural state (in veins & alluvial deposits), and is often separated from rocks and other minerals by mining & panning (wash gravel in a pan to separate out (gold)) operations.

Some minerals contains gold, such as: Calaverite (AuTe₂), Krennerite (AuTe₂, varing to 0.8 %to 0.2%), Nagyagite (Pb₅Au(Te,Sb)₄S_5-8), Petzite (Ag₃AuTe₂), Sylvanite (Ag,Au)Te₂, and the rare minerals are Maldonite (Au₂Bi), Aurostibite (AuSb₂), and also occurs in rare alloys Like Auricupride (Cu₂Au), Novodneprite (AuPb₃), Weishanite ((Au, Ag)₃Hg₂).

Seawater contains gold about or 0.1 to 2 mg/ton or 4 gm per million (1,000,000) tones of water.
Overall this is a huge amount of gold stored in the oceans, but because of the low concentration, attempts to reclaim this gold have always failed, where no method has been found yet for recovering gold from sea water profitably.

Gold is recovered from its ores by amalgamating, cyaniding, and smelting processes.
Refining is also frequently done by electrolysis (chemical decomposition).

Annual world wide production of Gold is around 2,800 tons, and World wide Reserve is around 187,200 tons.
6×10^-8% (In Universe)
1.7×10^-5% (In Meteorites)
1×10^-7% (In Sun)
3.1×10^-7% (In Earth’s Crust)
5×10^-9% (In Oceans)
0.00001% (In Humans)