GOLDPhysical properties:Gold is a soft metal with a number of interesting physical properties. Gold is both malleable and ductile. Gold is a heavy metal (density 19.3 g cm-3) and one gram of gold can be hammered out into a thin sheet of gold a metre in area, and just 230 atoms or so thick. Gold leaf is translucent and the transmitted light is greenish blue (gold metal reflects yellow and red, leaving the greenish blue colour. One gram of gold can be drawn into a thin wire 165 metres long and just 20 micrometres thick. X-ray data suggest electrons from filled d bands near the electron energy surface of the s-p conduction band are excited by near ultraviolet and blue energies, giving rise to the characteristic gold colour of the metal.

Chemical properties : As we go into the details of chemical properties of gold, you will understand the connection between the general and physical properties discussed above. Gold is considered to be a noble metal. It is chemically inactive. This is because it is highly resistant to react with other elements. The oxidation state of gold ranges from -1 to +5. The +1 and +3 [Au(I) and Au(III)] are the most common oxidation states of gold. Gold tends to form an amalgamation with mercury instead of reacting to create new compounds. It is resistant to the effect of most acids and therefore does not corrode easily. Gold can however be affected by 3:1 mixture of hydrochloric acid and nitric acid, called aqua regia. So, generally speaking gold is not a highly reactive compound. Apart from acids, gold does not combine with

oxygen, halogens, etc. easily. Aurous (univalent) and auric (trivalent) are two types of compounds formed by gold.

Uses: Gold has been used for centuries for jewellery and decoration. In addition to the more familiar rings, brooches, necklaces, and ear rings, gold is used as gold leaf for decoration and protection, screen printing (directly on to bone china, earthenware, porcelain, and glass surfaces or decals). Pure gold (100%, 24 carat) is not ideal for jewllery because it is rather soft. Recently a 99:1 by weight alloy of gold and titanium has been developed. This is known as 990 gold-titanium and it is very durable making it suitabkle for both coinage and jewllery. The alloy is made as follows. Gold (99.99% pure) is loaded into an alumina or zirconia crucible in a vacuum-induction furnace. The vacuum chamber is evacuated and heated at 8008C until most of the air is removed and then back-filled with argon. The gold is melted and heated to 13008C then a titanium block (99.7% pure) with a mass of 1% of that of the gold is dropped into the melt. This brings about a flash of light (origin unknown) during the dissolution process. The molten alloy is then cast in a graphite or ceramic mould and the casting cooled before exposure to the atmosphere. [G. Gafner, "The development of 990 gold-titanium, and its production, use, and properties", J. S. Afr. Inst Min. Metall., 1989, 89, 173-181.]

Gold is expensive but currently less so than platinum. This ring is 18K (18

carat) meaning the metal is 75% gold (24K is 100%).

Gold is the key component for "liquid gold", preparations containing up to

12% gold ideal for decorative application using brushes and gold pastes

used for screen printing. The UtiliseGold directory contains many links to

gold suppliers and products for these gold applications and those outlined

below.

Gold is also well known as a coinage metal (because of its scarcity,

inertness, and decorative features) and is a standard for monetary systems

in many countries. Apart from gold coins, gold ingots, and gold bars, gold

is available in many forms including pure gold and alloys as gold flakes,

foil gauzes (meshes), grain, powders, sheet, sponges, tubes, wires and

even single gold crystals.

Purple of Cassius is a purple pigment formed by the reaction of gold(III)

salts with tin(II) chloride. It imparts a red colour to glass (cranberry glass),

and also acts as a chemical test to determine the presence of gold.

Generally, the preparation of this material involves gold being dissolved in

aqua regia, then reacted with a solution of tin(II) chloride. The tin(II)

chloride reduces the chloroauric acid from the dissolution of gold in aqua

regia to a red or purple colloid of elemental gold. When used as a test, the

intensity of the colour correlates with the concentration of gold present.

See L. B. Hunt, "The True Story of Purple of Cassius", Gold Bulletin,

1976, 9, 134-139.

Recently, gold catalysts as gold supported on carbon or metal oxides are

becoming useful in the chemical industry. Many other gold compounds

including neutral gold halides (AuBr3, etc.), aurates (K[AuBr4], etc.) gold

cyanides, gold oxides, phosphine gold complexes, gold hydroxides and

gold nitrates are available to industrial users. Chlorauric acid (HAuCl4) is

used in photography for toning the silver image.

Gold is a really useful metal for electronics because of its inertness and

physical properties. Gold is used for electrical contacts, spring contacts,

bonding wire, solder alloys, bonding wire, bumping wire, electroplating,

and sputtering targets. Gold is also a useful brazing material. Gold is used

for coating space satellites, as it is a good IR reflector and is inert.

Since gold is inert and possesses useful properties when alloyed, gold is

used extensively for dentistry in gold teeth, dental attachments, inserts,

and solders. Similarly, gold is used increasingly for medical implants in

eyes and ears, as well as many other medically useful wires, tubes, sheets,

and foils. Disodium aurothiomalate is administered (intramuscular) as a

treatment for arthritis. The gold isotope 198Au is used for treating cancer and

other conditions.

Gold is used in nanotechnology applications as colloids, conjugates,

nanoparticle inks, nanoparticle solutions, and nanopowders.

COPPER

Physical properties: 1. Copper has a characteristic reddish brown colour.

2. Its density is 8.93 g cm-3.

3. Its melting point is 1083`C.

4. It is highly malleable and ductile at ordinary temperature. It becomes brittle near melting point.

5. It is a very good conductor of heat and electricity.

6. Its conductivity is almost as much as that of silver, the best conductor among all the metals.

Chemical properties: Like other metals, copper oxides

whenever it is exposed to the air. That is, the copper

reacts to oxygen in the air, not so much the moisture,

and it creates a verdigris that cakes onto the copper.

This verdigris is not like the rust that forms on iron or

other metals, but actually layers, covers, and even

protects the copper beneath it.

The misconception is that copper reacts to the water,

when really it’s the oxygen in the water that it reacts

to. The best example of this is the Statue of Liberty,

which was made from pure copper and has since

turned into a sea foam greenish color.

Copper also tarnishes when exposed to different

sulfides, and thus creates different copper sulfides.

These are simply different chemical compounds of

sulfur and copper. For more advanced study there is a

course specifically for GCSE

Chemistry  engineered for chemistry students that

specializes in how to use chemicals for the production

of different products.Uses: Copper is tough, malleable and highly conductive, making it one of the world's most important metals.

Copper is essential to all living things and plays an important role in modern technology. It has served humanity for 7,000 years, yet is still a modern metal. Electric power and electronics, the basis of today's society, are founded on the excellent ability of copper to conduct electricity. Nearly half of all copper is used for this purpose. Other important areas of consumption are the building, workshop and processing industry. The primary use for copper within the car industry is for car

radiators and electronics. Shipbuilding, the offshore industry and desalination plants are other copper markets. There is also a very useful alloy of copper and zinc that is brass.

In addition, Copper is a very big recycling metal. Nearly 90 per cent of the available scrap is recycled.

Pure copper oxidises very slowly. Copper cylinders are therefore used to store spent nuclear fuel. A copper cylinder with 10 cm thick walls will last for one million years before oxidising through.

Copper is shipped to fabricators mainly as cathode, wire rod, billet, cake (slab), or ingot. Through extrusion, drawing, rolling, forging, melting, electrolysis, or atomization, fabricators can form wire, rod, tube, sheet, plate, strip, castings, powder, and other shapes. These copper and copper-alloys are then shipped to manufacturing plants that make products to meet society's needs.

ZINCPhysical properties: