COPPER

Name: Copper

Symbol: Cu

Group: 11

Period: 4

Block: d

Category: Transition Metals

Atomic Number: 29

Atomic Mass: 63.546 u

Electrons per Shell: 2, 8, 18, 1

Electronegativity: 1.90

Density: 8.96 g/cc

Melting Point: 1084.62ºC

Boiling Point: 2562ºC

Thermal Conductivity: 400 W (m·K)

Electrical Conductivity: 5.9 × 10^7 S/m

Magnetic Order: Diamagnetic

Ordinary State: Solid

Oxidation States: -2, 1, 2, 3, 4

Mohs Hardness: 3

Vickers Hardness: 369 MPa

Brinell Hardness: 874 MPa

Most stable isotopes: Cu-63 (69.15%), Cu-65 (30.85%)

Discoverer: Known since ancient times

To speak of the history of copper is to delve into a narrative as ancient as humanity itself. Summarizing its impact in a few lines is a challenge, as this chemical element, essential in countless fields, has shaped the technical and cultural progress of civilizations. From modern electronics to mechanics and biochemistry, copper is a fundamental pillar that has sustained centuries of innovation and discovery. Its relevance transcends disciplines, solidifying its position as one of humanity's most valuable metals.

Copper was the first metal that humans learned to work on a large scale, marking the beginning of the Age of Metals, a period that still defines our era. Thousands of years ago, civilizations discovered in this reddish metal a versatile ally. With it, they forged sharp weapons, resistant armor, everyday utensils, and structural components that shaped their societies. Its malleability and conductivity made it an ideal material for innumerable applications, from primitive tools to complex modern systems. The metallurgy of copper not only transformed ancient technology but also opened the doors to advancements that continue to drive science and industry.

Today, copper remains indispensable. In electrical cables, machinery, jewelry, or even medicine, its presence is ubiquitous. The history of copper is, in essence, the story of how a simple yet extraordinary metal allowed humanity to leap into modernity, a legacy that continues to evolve with every new discovery.

There is archaeological evidence of objects made of almost pure copper dating back to at least 6000 BC, found in different regions of the planet. These dates are surprising if we consider that, for example, rhenium — another metal — was first isolated in 1925.

The reason for copper's early and abundant use is clear from a metallurgical point of view: it is an abundant element, present in nature in its native state, and most importantly, it can be obtained with great purity through direct reduction with carbon, one of the simplest methods to extract a metal from its ore. Furthermore, being found in its native state, it could simply be melted and molded. Copper, being a semi-noble metal, offered significant advantages: it could be cast in molds and worked with relative ease compared to other metals. It is soft, ductile, malleable, and resistant to corrosion.

Thanks to these properties, copper pieces and proto-alloys like arsenical bronze have survived to this day in good condition, unlike iron artifacts of the same antiquity, which rarely preserve due to corrosion.

The discovery and mastery of copper radically transformed human life. Before it, tools and weapons were limited to sticks, stones, and natural materials like flint, used for spearheads. Although these primitive solutions offered some advantage against predators, they were largely ineffective in conflicts between humans. Copper, on the contrary, could be "tamed" with fire and molded into spears, shields, swords, and arrowheads, providing decisive military advantages. Tribes that developed copper weaponry easily surpassed those still using stone and wood.

This point is essential: the history of copper cannot be separated from the history of war. Since the dawn of humanity, technology has been a means to overcome obstacles, protect family, and ensure survival. Contrary to popular belief, the military concept was not born with steel, but with copper. Although in its pure state it is softer than other metals, its superiority over stone and wood weapons marked a before and after in the struggle for power.

In the tribal era, mastery of copper meant the ability to prevail not only over stronger animals but also over human rivals. Humans lack powerful claws or fangs, so they relied on their intellect to create tools that compensated for these deficiencies. Thus, tribes with better weapons secured fertile territories, resources, and social standing. In this way, hierarchies, military castes, kings, and power structures based on military force emerged.

It is important to understand this historical reality without idealizing it: better weapons have always meant greater chances of success. Copper was the first great technological revolution that granted military supremacy to certain human groups, a pattern that continues today with other technologies. Yesterday it was copper; today, it is advanced defense systems and modern weapons.

In short, copper did not just mold tools and vessels: it molded entire civilizations. Its technical mastery was the cradle of organized warfare, a factor that, whether we like it or not, has determined the course of human history since its origins.

In its early uses, copper was worked in an almost pure state or in simple alloys with small amounts of silver and/or gold. However, the first "technical" alloys soon emerged, mostly discovered accidentally, typical of those primitive times when metallurgy was still unknown territory. Copper, initially soft and malleable, began to be combined with other chemical elements that significantly improved its hardness and toughness.

It is not known with certainty where or when someone accidentally mixed copper with cassiterite (tin ore) in the same furnace, giving rise to the first bronze as we know it today. Alloys with arsenic were also developed, where its presence greatly hardened the metal. However, due to the toxicity of arsenic, its use was abandoned over time. In contrast, original bronze — copper + tin — continues to be used, although increasingly less due to its rising price.

It is fascinating to think that we are talking about an alloy that has remained almost unaltered for more than five millennia. Long before Rome was even a village, a vast trade in copper and bronze already existed in the Mediterranean basin and the Arabian Peninsula. Classical bronze quickly became the reference material in the military sphere, marking the end of the Copper Age and the beginning of the Bronze Age.

The difference between both eras was not absolute: for objects and utensils that did not require great hardness, pure copper continued to be used. Tin, scarcer and more valuable, was reserved for manufacturing stronger weapons and armor, such as helmets, shields, spears, and knives. Even in Ancient Egypt, copper played a key role in the construction of the pyramids and in the crafting of tools and ornaments, occasionally complemented by iron-nickel from meteorites.

The dominance of bronze lasted for centuries. Even in Roman times, it remained the base material for manufacturing much of the military equipment: shields, breastplates, and helmets. However, with the advent of steel, the comparison proved disadvantageous. Although copper is corrosion-resistant and very malleable, its strength and mechanical resistance could not compete with steel, leading to a rapid decline in its offensive military use.

Even so, copper and bronze continued to have essential applications in daily life: manufacturing amphoras, vessels, utensils, aqueducts, jewelry (along with silver and gold), mirrors, statues, and countless objects. Their versatility made these alloys fundamental materials not only in warfare but also in the cultural and economic development of ancient civilizations.

Copper, known as the red metal, stands out for its relative abundance in the Earth's crust, especially when compared to precious metals like silver or gold. However, compared to other elements of the first transition series, such as titanium or magnesium, its presence is less dominant. What makes copper seem so accessible is not just its quantity, but the ease with which it is extracted and processed compared to more common but more complex-to-obtain metals. This characteristic has made it an essential resource for humanity from ancient times to the modern era.

Chile leads global copper production by a wide margin, followed by Peru and the United States. These countries not only dominate extraction in the Americas but also house the largest global reserves, consolidating their position as powers in the copper industry. In other regions, such as southern Africa, copper is also abundant, although its exploitation often takes a back seat to metals of greater economic value, such as gold, silver, tantalum, or niobium. Despite this, copper's availability and versatility keep it a fundamental pillar of metallurgy and technology, driving everything from infrastructure to cutting-edge innovations.

Copper is the most malleable, ductile, dense, and chemically noble metal within the first transition series of the periodic table. It exhibits a unique crystal structure: face-centered cubic (FCC), which remains stable at any temperature. Its characteristic red color and ease of obtaining — through direct reduction with carbon or aluminum, as in the thermite process — have made it a fundamental resource since antiquity.

It is highly resistant to corrosion in reducing environments and stands out as an excellent conductor of heat and electricity: it is the second-best conductor among all metals, only surpassed by silver, and the third on the general scale if carbon (graphite) is included. It possesses a strong diamagnetic character, meaning it repels magnetic fields and is difficult to polarize. Currently, it is one of the most expensive non-precious metals, with a rising price due to the industrial and technological expansion of new economies that depend on it for its exceptional thermal and electrical conductivity properties.

On the mechanical front, copper presents outstanding qualities: great ductility and malleability, ease of work through multiple manufacturing processes, a relatively low melting point (1084 °C), and high recyclability. Additionally, it possesses a property little known to the general public: it is a natural antimicrobial agent, capable of actively eliminating bacteria that come into contact with its surface.

This metal is obtained from numerous minerals, although it also appears in its native state, which evidences its chemical nobility. It is a typical chalcophile, with a strong affinity for sulfur and its compounds. It does not react with carbon, boron, or nitrogen under normal conditions, so no stable copper carbides, borides, or nitrides are known. It does react with all chalcogens (especially sulfur), beryllium, aluminum, and silicon.

Regarding its alloying capacity, with exceptions such as nickel or manganese, it presents difficulties in combining with most transition metals close to iron, including refractory metals (like tungsten) and those of the platinum group (like ruthenium). However, it forms stable compounds with precious metals such as palladium, platinum, and, of course, the other two members of its group: silver and gold. It has a great affinity with tin and indium, but not with lead or bismuth, metals with which it is not soluble. It also easily alloys with metals of group 12 (zinc, cadmium, and mercury) in any proportion.

Copper, with its characteristic reddish luster, is a metal that captivates at first sight, but its interaction with the environment reveals an even more fascinating quality: its notable resistance to corrosion. Over time, this metal develops a patina, a protective layer that transitions from blackish to green or bluish tones, like the iconic milky green that covers the Statue of Liberty in New York. This structure, formed by high-purity copper sheets supported by a steel frame, is an emblematic example of how copper not only resists the passage of time but transforms into a symbol of durability.

Chemically, copper is classified as a semi-noble metal, which grants it exceptional resistance in various environments. At room temperature and under dry conditions, it does not react with halogens, including fluorine, until temperatures exceed 100 °C. In seawater, even at elevated temperatures, it remains unaltered, except when combined with more noble metals like silver or gold, which can trigger galvanic corrosion. Reducing acids, such as hydrofluoric or hydrochloric, barely affect it. However, copper is vulnerable in oxidizing environments, such as nitric acid, which attacks it even in low concentrations.

Copper's true strength lies in its resistance to alkaline bases, reducing media, and biological attacks. Unlike metals such as iron, nickel, or aluminum, which can be degraded by bacteria in saline environments, copper remains immune. Its ability to form a protective layer makes it resistant to organic substances and environmental factors, adopting colors that vary according to the chemical composition of the patina, with green being the most recognized. This layer not only preserves the metal but also confers a unique aesthetic character. Curiously, the structure of the Statue of Liberty is not only a testament to this resistance but also acts as a natural lightning rod and, in a way, as a colossal galvanic cell, a phenomenon we will explore later.

Copper is the fourth most used metal worldwide, only surpassed by steel (iron alloy), aluminum, and magnesium. It is one of the most versatile metals, with a wide variety of applications thanks to being affordable, easy to work with, and known to humanity for millennia. In fact, it was the first metal used by humans.

In antiquity, when quality steel was a scarce commodity, copper and its alloys were used for structural purposes. Before the German-British Industrial Revolution, steel displaced copper in the manufacture of weapons and armor, but it was never cheaper than iron except in exceptional cases, such as very complex steel parts. For a time, copper was relegated until the electrical industry rescued it as an essential material, a role it maintains to this day. Today, solid copper has given way to copper primarily used for electrical and, secondarily, thermal conduction.

In the electrical field, it is the most widely used conductive metal globally (although aluminum has been gaining ground for cost reasons). It is used in the manufacturing of cables and wires, coils, electronic components, circuits of all kinds, urban lighting systems, and electrical installations in buildings. This sector is, by far, the largest consumer of copper in the world.

As a thermal conductor, copper has more specific applications. A everyday example is certain high-quality pressure cookers that incorporate an internal layer of copper between two layers of stainless steel, which improves heat transmission and accelerates cooking time.

Taking advantage of its corrosion resistance, copper is used as a pre-coating before nickel plating or chrome plating, applied to bare steel before receiving other protective layers. Due to its harmlessness, it is also used in the manufacturing of pipes, although this use has currently decreased in favor of PVC, which offers a better quality-price ratio. Historically, copper was used to make pots, cauldrons, and culinary utensils, although its direct use is now avoided due to the toxicity of the patina that forms on its surface if not cleaned properly.

In the manufacturing of electric generators, copper is combined with iron and zinc to form electrochemical cells that produce electricity thanks to the flow of electrons between the metals.

A little-known fact is that pure copper is a natural antimicrobial agent. It is capable of destroying bacteria and other microscopic microorganisms through an ionization process, without harming human tissues. This principle is also applied in medical devices such as the IUD (intrauterine device), where copper acts as a chemical barrier against spermatozoa. However, this method is not infallible and must be considered within an appropriate medical context.

Thanks to this same ability to repel organisms, copper is highly resistant to attack by mollusks, fungi, and marine bacteria that degrade materials like steel. This property made it valuable in the naval industry, where the British were pioneers in coating ship hulls with copper sheets to prolong their lifespan. Sometimes, lead was used as a substitute, either due to the high cost of copper or its scarcity. From this historical use derives the English expression "copper-bottomed," which means "risk-proof" or "guaranteed."

Copper is one of the so-called seven metals of antiquity, present in the first treatises on the use and handling of metals in various cultures, even those separated by great geographical distances. It was probably the first metal worked by humanity, due to its abundance and the ease with which it could be obtained in its native state. In most ancient civilizations around the world, copper preceded the use of other metals like iron or tin.

Its unique color, usually described as red or reddish — with nuances ranging from a bright pink in freshly melted copper to a characteristic dark red from oxidation — has made it an easily recognizable material. Although copper corrodes like all non-precious metals, it does so in a controlled manner, forming a surface layer known as patina. This film, highly valued by collectors of coins, medals, and ancient objects, is a natural mark of the metal's aging and can increase its historical and aesthetic value (for example, in coins from the 10th century). While patina can be easily removed with citric acid present in lemon juice, it is not recommended to do so when dealing with pieces of historical or numismatic value.

In alchemical symbolism, copper shares a symbol with the feminine gender: a circle over a cross. While the masculine sign (circle with an arrow) represents attributes like the sword or spear, the sign of copper symbolizes femininity and the vulva.

In Western cultural tradition, copper is associated with the planet Venus and, by extension, with the goddess Aphrodite, reinforcing its symbolic link with the feminine, beauty, and harmony. This parallelism contrasts with that of iron, associated with Mars/Ares, war, and the masculine.

Copper's link to history is also reflected in toponymy: the Latin name cuprum (origin of the chemical symbol "Cu" in the periodic table) comes from aes cyprium, "metal of Cyprus," because this island was an abundant source of copper during Roman times. Conversely, it can be said that the metal's name itself derives from the close relationship between Cyprus and its mineral wealth.

This connection between copper, mythology, astrology, and alchemy is a reminder that disciplines today considered "pseudoscience" were, at one time, pillars of the development of astronomy, cultural history, and chemistry. Modern science, whether some of its more skeptical practitioners like it or not, has deep roots in these ancestral knowledges.