COPPER: HISTORY, PROPERTIES, STRUCTURE, USES, BIOLOGICAL ROLE - CHEMISTRY - 2024

The copper is a transition metal belonging to group 11 of the periodic table and is represented by the chemical symbol Cu. It is characterized and distinguished by being a red-orange metal, very ductile and malleable, being also a great conductor of electricity and heat.

In its metallic form it is found as a primary mineral in basaltic rocks. Meanwhile, it is oxidized in sulfurous compounds (those of greater mining exploitation), arsenides, chlorides and carbonates; that is, a vast category of minerals.

Alarm clock made of copper. Source: Pixabay.

Among the minerals that contain it, we can mention chalcocite, chalcopyrite, bornite, cuprite, malachite and azurite. Copper is also present in the ash of algae, in marine corals and in arthropods.

This metal has an abundance of 80 ppm in the earth's crust, and an average concentration in seawater of 2.5 ∙ 10 ^-4 mg / L. In nature it occurs as two natural isotopes: ⁶³ Cu, with an abundance of 69.15%, and ⁶⁵ Cu, with an abundance of 30.85%.

There is evidence that copper was smelted in 8000 BC. C. and alloyed with tin to form bronze, in 4000 BC. C. It is considered that only meteoric iron and gold precede it as the first metals used by man. It is thus synonymous with archaic and orange glow at the same time.

Copper is used mainly in the manufacture of cables for conducting electricity in electric motors. Such cables, small or large, make up machinery or devices in industry and in everyday life.

Copper is involved in the electronic transport chain that allows the synthesis of ATP; main energy compound of living beings. It is a cofactor of superoxide dismutase: an enzyme that degrades the superoxide ion, a compound highly toxic to living beings.

In addition, copper plays a role in hemocyanin in oxygen transport in some arachnids, crustaceans and mollusks, which is similar to that performed by iron in hemoglobin.

Despite all its beneficial actions for man, when copper accumulates in the human body, such is the case of Wilson's disease, it can cause cirrhosis of the liver, brain disorders and eye damage, among other alterations.

History

Copper age

Native copper was used to make artifacts as a substitute for stone in the Neolithic, probably between 9000 and 8000 BC. C. Copper is one of the first metals used by man, after the iron present in meteorites and gold.

There is evidence of the use of mining in obtaining copper in the year 5000 BC. C. Already for a previous date, articles of copper were constructed; such is the case of an earring made in Iraq estimated to be 8700 BC. C.

In turn, it is believed that metallurgy was born in Mesopotamia (now Iraq) in 4000 BC. C., when it was possible to reduce the metal of the minerals through the use of fire and coal. Later, copper was intentionally alloyed with tin to produce bronze (4000 BC).

Some historians point to a Copper Age, which would be located chronologically between the Neolithic and the Bronze Age. Later, the Iron Age replaced the Bronze Age between 2000 and 1000 BC. C.

Bronze age

The Bronze Age began 4000 years after copper was smelted. Bronze items from the Vinca culture date back to 4500 BC. C.; while in Sumeria and Egypt there are bronze objects made 3000 years BC. C.

The use of radioactive carbon has established the existence of copper mining in Alderley Edge, Cheshire and the United Kingdom, between the years 2280 and 1890 BC. C.

It can be noted that Ötzi, the "Ice Man" with an estimated date between 3300 and 3200 BC. C., had an ax with a head of pure copper.

The Romans from the 6th century BC. They used pieces of copper as currency. Julius Caesar used coins made of brass, copper and zinc alloy. Furthermore, Octavian's coins were made with an alloy of copper, lead, and tin.

Production and name

Copper production in the Roman Empire reached 150,000 tons per year, a figure only surpassed during the Industrial Revolution. The Romans brought copper from Cyprus, knowing it as aes Cyprium ("metal from Cyprus").

Later, the term degenerated into cuprum: a name used to designate copper until the year 1530, when the English root term 'copper' was introduced to designate the metal.

The Great Copper Mountain in Sweden, which operated from the 10th century to 1992, covered 60% of Europe's consumption in the 17th century. The La Norddeutsche Affinerie plant in Hamburg (1876) was the first modern electroplating plant to use copper.

Physical and chemical properties

Appearance

Copper is a lustrous orange-red metal, while most native metals are gray or silver.

Atomic number (Z)

29

Atomic weight

63,546 u

Melting point

1,084.62 ºC

Common gases such as oxygen, nitrogen, carbon dioxide, and sulfur dioxide are soluble in molten copper and affect the mechanical and electrical properties of the metal when it solidifies.

Boiling point

2,562 ºC

Density

- 8.96 g / mL at room temperature.

- 8.02 g / mL at melting point (liquid).

Note that there is no considerable decrease in density between the solid and liquid phase; both represent very dense materials.

Heat of fusion

13.26 kJ / mol.

Heat of vaporization

300 kJ / mol.

Molar caloric capacity

24.44 J / (mol * K).

Thermal expansion

16.5 µm / (m * K) at 25 ° C.

Thermal conductivity

401 W / (m ∙ K).

Electrical resistivity

16.78 Ω ∙ m at 20 ° C.

Electric conductivity

59.6 ∙ 10 ⁶ S / m.

Copper has a very high electrical conduction, only surpassed by silver.

Mohs hardness

3.0.

It is therefore a soft metal and also quite ductile. Strength and toughness are increased by cold working due to elongated crystal formation of the same face-centered cubic structure present in copper.

Chemical reactions

Copper flame test, which is identified by the color of its blue-green flame. Source: Swn (https://commons.wikimedia.org/wiki/File:Flametest-Co-Cu.swn.jpg)

Copper does not react with water, but it does react with atmospheric oxygen, being covered with a layer of black-brown oxide that provides corrosion protection to the underlying layers of the metal:

2Cu (s) + O ₂ (g) → 2CuO

Copper is not soluble in dilute acids, however it reacts with hot and concentrated sulfuric and nitric acids. It is also soluble in ammonia in aqueous solution and in potassium cyanide.

It can resist the action of atmospheric air and sea water. However, its prolonged exposure results in the formation of a thin green protective layer (patina).

The previous layer is a mixture of carbonate and copper sulfate, observed in old buildings or sculptures, such as the Statue of Liberty in New York.

Copper reacts heated to red with oxygen to give cupric oxide (CuO) and at higher temperatures forms cuprous oxide (Cu ₂ O). It also reacts hot with sulfur to produce copper sulfide; therefore, it becomes foggy when exposed to some sulfur compounds.

Copper I burns with a blue flame in a flame test; while copper II emits a green flame.

Structure and electronic configuration

Copper crystals crystallize in the face centered cubic (fcc) structure. In this fcc crystal, the Cu atoms remain attached thanks to the metallic bond, which is comparatively weaker than other transition metals; a fact manifested in its great ductility and low melting point (1084 ºC).

According to the electronic configuration:

3d ¹⁰ 4s ¹

All 3d orbitals are filled with electrons, while there is a vacancy in the 4s orbital. This means that the 3d orbitals do not collaborate in the metallic bond as one would expect from other metals. Thus, the Cu atoms along the crystal overlap their 4s orbitals to create bands, influencing the relatively weak force of their interactions.

In fact, the resulting energetic difference between the 3d (full) and 4s (half-full) orbital electrons is responsible for the copper crystals absorbing photons from the visible spectrum, reflecting their distinctive orange color.

Copper fcc crystals can have different sizes, which, the smaller they are, the stronger the metal piece will be. When they are very small, then we speak of nanoparticles, sensitive to oxidation and reserved for selective applications.

Oxidation numbers

The first number or oxidation state that can be expected of copper is +1, due to the loss of the electron from its 4s orbital. When having it in a compound, the existence of the Cu ⁺ cation (commonly called the cuprous ion) is assumed.

This and the oxidation number +2 (Cu ²⁺) are the best known and most abundant for copper; they are generally the only ones taught at the high school level. However, there are also the oxidation numbers +3 (Cu ³⁺) and +4 (Cu ⁴⁺), which are not as rare as you might think at first glance.

For example, the salts of the cuprate anion, CuO ₂ ^-, represent compounds with copper (III) or +3; such is the case of potassium cuprate, KCuO ₂ (K ⁺ Cu ³⁺ O ₂ ^2-).

Copper also, although to a lesser degree and on very rare occasions, can have a negative oxidation number: -2 (Cu ^2-).

How is it obtained

Raw material

The minerals most used for copper extraction are metal sulphides, mainly chalcopyrite (CuFeS ₂) and bornite (Cu ₅ FeS ₄). These minerals contribute 50% of the total copper extracted. Calellite (CuS) and chalcocite (Cu ₂ S) are also used to obtain copper.

Crushing and grinding

Initially the rocks are crushed to obtain rocky fragments of 1.2 cm. Then it continues with a grinding of the rocky fragments, until obtaining particles of 0.18 mm. Water and reagents are added to obtain a paste, which is then floated to obtain a copper concentrate.

Floatation

In this stage, bubbles are formed that trap copper and sulfur minerals that are present in the pulp. Several processes are carried out to collect the foam, drying it to obtain the concentrate that continues its purification.

Purification

To separate copper from other metals and impurities, the dry concentrate is subjected to high temperatures in special furnaces. Fire refined copper (RAF) is molded into plates weighing approximately 225 kg that will constitute anodes.

Electrolysis

Electrolysis is used in the refining of copper. The anodes from the smelter are taken to electrolytic cells for refining. Copper travels to the cathode and impurities settle to the bottom of the cells. In this process copper cathodes with 99.99% purity are obtained.

Copper alloys

Bronze

Bronze is an alloy of copper and tin, with copper constituting between 80 and 97% of it. It was used in the manufacture of weapons and utensils. It is currently used in the manufacture of mechanical parts resistant to friction and corrosion.

In addition, it is used in the construction of musical instruments, such as bells, gongs, cymbals, saxophones and strings of harps, guitars and piano.

Brass

Brass is an alloy of copper and zinc. In industrial brasses the percentage of zinc is less than 50%. It is used in the elaboration of containers and metallic structures.

Monel

Monel alloy is a nickel-copper alloy, with a 2: 1 ratio of nickel to copper. It is resistant to corrosion and is used in heat exchangers, rods and lens arches.

They confirmed

Constatán is an alloy made up of 55% copper and 45% nickel. It is used to make coins and is characterized by having a constant resistance. Also cupro-nickel alloy is used for the outer coating of small denomination coins.

BeCu

The copper-beryllium alloy has a beryllium percentage of 2%. This alloy combines strength, hardness, electrical conductivity, and corrosion resistance. The alloy is commonly used in electrical connectors, telecommunications products, computer components, and small springs.

Tools such as wrenches, screwdrivers and hammers used on oil rigs and coal mines have the initials BeCu as a guarantee that they will not produce sparks.

Other

The alloy silver 90% and copper 10% was used in coins, until 1965 when the use of silver was eliminated in all currencies, except for the half dollar coin.

7% copper aluminum alloy is golden in color and is used in decoration. Meanwhile, Shakudo is a Japanese decorative alloy of copper and gold, in a low percentage (4 to 10%).

Applications

Electrical wiring and motors

Copper electrical wiring. Source: Scott Ehardt

Copper due to its high electrical conduction and low cost is the metal of choice for use in electrical wiring. The copper cable is used in the various stages of electricity, such as electric power generation, transmission, distribution, etc.

50% of the copper produced in the world is used in the production of electrical cables and wires, due to its high electrical conductivity, ease of forming wires (ductility), resistance to deformation and corrosion.

Copper is also used in making integrated circuits and printed circuit boards. Metal is used in heat sinks and heat exchangers due to its high thermal conduction, which facilitates heat dissipation.

Copper is used in electromagnets, vacuum tubes, cathode ray tubes, and magnetrons in microwave ovens.

Likewise, it is used in the construction of the coils of electric motors and the systems that put the motors to work, these items representing around 40% of the world's electricity consumption.

Building

Copper, due to its resistance to corrosion and the action of atmospheric air, has been used for a long time in the roofs of houses, downspouts, domes, doors, windows, etc.

It is currently used in wall cladding and decorative items, such as bathroom accessories, door handles, and lamps. Also, it is used in antimicrobial products.

Biostatic action

Copper prevents numerous life forms from growing on top of it. It was used in sheets that were placed on the bottom of the hulls of ships to prevent the growth of mollusks, such as mussels, as well as barnacles.

Currently copper-based paints are used for the aforementioned protection of ship hulls. Metallic copper can neutralize many bacteria on contact.

Its mechanism of action has been studied based on its ionic, corrosive and physical properties. The conclusion was that the oxidizing behavior of copper, together with the solubility properties of its oxides are the factors that cause metallic copper to be antibacterial.

Metallic copper acts on some strains of E. coli, S. aureus and Clostridium difficile, group A viruses, adenoviruses and fungi. Therefore, it has been planned to use copper alloys that are in contact with the hands of passengers in different means of transport.

Nanoparticles

The antimicrobial action of copper is further enhanced when its nanoparticles are used, which have proven useful for endodontic treatments.

Likewise, copper nanoparticles are excellent adsorbents, and because they are orange, a color change in them represents a latent colorimetric method; for example, developed for the detection of dithiocarbamates pesticides.

Biological role

In the electronic transport chain

Copper is an essential element for life. It is involved in the electronic transport chain, forming part of complex IV. The final step of the electronic transport chain takes place in this complex: the reduction of the oxygen molecule to form water.

Complex IV is made up of two hae groups, a cytochrome a, a cytochrome a ₃, as well as two Cu centers; one called CuA and the other CuB. Cytochrome a ₃ and CuB form a binuclear center, in which the reduction of oxygen to water occurs.

In this stage, Cu passes from its +1 to +2 oxidation state, giving electrons to the oxygen molecule. The electronic transport chain uses NADH and FADH ₂, from the Krebs cycle, as electron donors, with which it creates an electrochemical hydrogen gradient.

This gradient serves as an energy source for the generation of ATP, in a process known as oxidative phosphorylation. So, and ultimately, the presence of copper is necessary for the production of ATP in eukaryotic cells.

In the enzyme superoxide dismutase

Copper is part of the enzyme superoxide dismutase, an enzyme that catalyzes the decomposition of the superoxide ion (O ₂ ^-), a compound toxic to living beings.

Superoxide dismutase catalyzes the decomposition of the superoxide ion into oxygen and / or hydrogen peroxide.

Superoxide dismutase can use the reduction of copper to oxidize superoxide to oxygen, or it can cause oxidation of copper to form hydrogen peroxide from superoxide.

In hemocyanin

Hemocyanin is a protein present in the blood of some arachnids, crustaceans and mollusks. It fulfills a similar function to hemoglobin in these animals, but instead of having iron at the site of oxygen transport, it has copper.

Hemocyanin has two copper atoms in its active site. For this reason, the color of hemocyanin is blue-green. The metallic copper centers are not in direct contact, but have a close location. The oxygen molecule is sandwiched between the two copper atoms.

Concentration in the human body

The human body contains between 1.4 and 2.1 mg of Cu / kg of body weight. Copper is absorbed in the small intestine and is then carried to the liver together with albumin. From there, copper is transported to the rest of the human body attached to the plasma protein ceruloplasmin.

The excess copper is excreted through the bile. In some cases, however, such as in Wilson's disease, copper accumulates in the body, manifesting toxic effects of the metal that affect the nervous system, kidneys and eyes.

References

1. Ghoto, SA, Khuhawar, MY, Jahangir, TM et al. (2019). Applications of copper nanoparticles for colorimetric detection of dithiocarbamate pesticides. J Nanostruct Chem 9: 77. doi.org/10.1007/s40097-019-0299-4
2. Sánchez-Sanhueza, Gabriela, Fuentes-Rodríguez, Daniela, & Bello-Toledo, Helia. (2016). Copper Nanoparticles as Potential Antimicrobial Agent in Disinfecting Root Canals: A Systematic Review. International journal of odontostomatology, 10 (3), 547-554. dx.doi.org/10.4067/S0718-381X2016000300024
3. Wikipedia. (2019). Copper. Recovered from: en.wikipedia.org
4. Terence Bell. (September 19, 2018). Physical properties of beryllium copper. Recovered from: thebalance.com
5. Helmenstine, Anne Marie, Ph.D. (July 03, 2019). Copper Facts: Chemical and Physical Properties. Recovered from: thoughtco.com
6. The Editors of Encyclopaedia Britannica. (July 26, 2019). Copper: chemical element. Encyclopaedia Britannica. Recovered from: britannica.com
7. Editor. (November 10, 2018). Chalcopyrite. Recovered from: mineriaenlinea.com
8. Lenntech BV (2019). Periodic table: copper. Recovered from: lenntech.com