Copper is a shiny, reddish-brown metal.
Credit: Zelenskaya | Shutterstock
Shiny, reddish copper was the first metal ever manipulated by humans, and it remains an important metal in industry today.
The oldest metal object found in the Middle East consists of copper (it was a tiny awl dating back as far as 5100 B.C.). The U.S. penny was originally made of pure copper (nowadays, it is 97.5 percent zinc with a thin copper skin). Copper ranks as third-most-consumed industrial metal in the world, after iron and aluminum, according to the U.S. Geological Survey. About three-quarters of that copper goes to make electrical wires, telecommunication cables and electronics.
Aside from gold, copper is the only metal on the periodic table whose coloring isn't naturally silver or grey. Read on for more about this malleable metal.
Just the facts
- Atomic number (number of protons in the nucleus): 29
- Atomic symbol (on the periodic table of elements): Cu
- Atomic weight (average mass of the atom): 63.55
- Density: 8.92 grams per cubic centimeter
- Phase at room temperature: Solid
- Melting point: 1,984.32 degrees Fahrenheit (1,084.62 degrees Celsius)
- Boiling point: 5,301 degrees F (2,927 degrees C)
- Number of isotopes (atoms of the same element with a different number of neutrons): 35; 2 stable
- Most common isotopes: Cu-63 (69.15 percent natural abundance) and Cu-65 (30.85 percent natural abundance)
Orange and green
Most copper occurs in ores and must be smelted for purity before it can be used. But natural chemical reactions do sometimes release native copper, according to Chemicool; this explains why humans have been making things from the metal for at least 8,000 years. People figured out how to smelt copper by about 4500 B.C., further increasing supplies. The next technological leap was creating copper alloys; by adding tin to copper, people made a harder metal: bronze. The technological development (which occurred at different times in different regions) ushered in the Bronze Age.
Copper artifacts are sprinkled throughout the historical record. A tiny awl, the oldest metal object ever found in the Middle East, was discovered buried with a middle-age woman in an ancient village in Israel. The copper probably came from the Caucasus region more than 620 miles (1,000 kilometers) away. In ancient Egypt, people used copper alloys to make jewelry, including toe rings. Researchers have found massive copper mines from the 10th century B.C. in Israel.
About two-thirds of the copper on Earth is found in igneous (volcanic) rocks. About a quarter occurs in sedimentary rocks, according to the USGS. The metal is ductile and malleable and conducts heat and electricity well, explaining its use in electronics and wiring.
Copper turns green because of an oxidation reaction; that is, it loses electrons when exposed to water and air. The resulting copper oxide is a dull green. This oxidation reaction is the reason the copper-plated Statue of Liberty is green rather than orange-red. According to the Copper Development Association, a weathered layer of copper oxide only 0.005 inches (0.127 millimeters) thick coats Lady Liberty. The covering weighs about 80 tons. The change from copper-colored to green occurred gradually and was complete by 1920, 34 years after the statue's construction, according to the New York Historical Society.
- If all of the copper wiring in an average car were laid out, it would stretch 0.9 miles (1.5 km), according to the USGS.
- Pennies were made of pure copper only from 1783 to 1837. For most of the coin's history, it has been made of bronze (95 percent copper, with 5 percent tin and zinc). Today, pennies are 97.5 percent zinc and 2.5 percent copper.
- People need copper in their diets. The metal is an essential trace mineral, crucial for forming red blood cells, according to the U.S. National Library of Medicine. Fortunately, most everyone gets enough copper from foods such as grains, beans, potatoes and leafy greens.
- Too much copper is a bad thing, though. Ingesting high levels of the metal can cause abdominal pain, vomiting and jaundice in the short term. Long-term exposure may lead to symptoms such as anemia, convulsions and diarrhea, which is often bloody and may be blue.
- Copper has antimicrobial properties and kills bacteria, viruses and yeasts on contact, according to a 2011 paper in the journal Applied and Environmental Microbiology. As a result, copper can even be woven into fabrics to make antimicrobial garments, like socks that fight foot fungus.
Medicine: Copper's antimicrobial properties have made it a popular metal in the medical field. Multiple hospitals have experimented with covering frequently touched surfaces, such as bed rails and call buttons, with copper or copper alloys in an attempt to slow the spread of hospital-acquired infections. Copper kills microbes by interfering with the electrical charge of the organisms' cell membranes, said Cassandra Salgado, a Medical University of South Carolina professor of infectious diseases and hospital epidemiologist.
In 2013, researchers led by Salgado tested copper surfaces in intensive care units in three hospitals. The scientists found that 12.3 percent of patients developed antibiotic-resistant infections (MRSA, methicillin-resistant Staphylococcus aureus, and VRE, vancomycin-resistant Enterococcus) in traditional rooms. In the copper-modified rooms, only 7.1 percent of patients contracted one of these potentially devastating infections.
"We know that if you put copper in a patient's room, you're going to decrease the microbial burden," Salgado told Live Science. "I think that's something that has been shown time and time again. Our study was the first to demonstrate that there could be a clinical benefit to this."
The researchers changed nothing else about the ICU conditions beyond the copper; doctors and nurses still washed their hands, and cleaning went on as usual. The researchers published their findings in 2013 in the journal Infection Control and Hospital Epidemiology.
Salgado and her team are now hoping to test the idea in other medical wards, particularly in areas where patients are more mobile than in the ICU. There also needs to be a cost-benefit analysis weighing the expense of copper installation against the savings gained by preventing costly infections, she said.
Electronics: Copper also plays a huge role in electronics, and because of its abundance and low price tag, researchers are working to integrate the metal into an increasing number of cutting-edge devices.
In fact, copper may help produce futuristic electronic paper, wearable biosensors and other "soft" electronics, said Wenlong Cheng, a professor of chemical engineering at Monash University in Australia. Cheng and his colleagues have used copper nanowires to create an "aerogel monolith," a material that is highly porous, very light and strong enough to stand up on its own. (Imagine a dry kitchen sponge.) In the past, these aerogel monoliths have been made from gold or silver, but copper is a more economical option.
By mixing copper nanowires with small amounts of poly(vinyl alcohol), or PVA, the researchers created aerogel monoliths that could turn into a sort of sliceable, shapeable rubber. However, this rubber conducts electricity. The researchers reported their findings in the journal ACS Nano. The ultimate result could be a soft-bodied robot, or a medical sensor that melds perfectly to curved skin, Cheng told Live Science. He and his team are currently working to create blood pressure and body temperature sensors out of copper aerogel monoliths — another way copper could help improve human health.
Physics: In a recent experiment, a chunk of copper became the coldest cubic meter (35.3 cubic feet) on Earth when researchers chilled it to 6 millikelvins, or six-thousandths of a degree above absolute zero (0 Kelvin). This is the closest a substance of this mass and volume has ever come to absolute zero.
Researchers at the Instituto Nazionale di Fisica Nucleare (INFN) in Italy put the 880-lb. (400 kilograms) copper cube inside a container called a cryostat that is specially designed to keep items extremely cold. This is the first cryostat built that is capable of keeping substances so close to absolute zero.
Building the extreme temperature cryostat is just the first step in a new experiment in which the cryostat will act as a particle detector. Researchers hope the detector will reveal more about the subatomic particles called neutrinos and why there is so much more matter than antimatter in the universe.
- The American Cancer Society examines the research about copper and claims that it may have a role in preventing or treating cancer.
- The Environmental Protection Agency provides information about exposure to high levels of copper and the effects of copper corrosion in household pipes.
- The Thomas Jefferson National Accelerator facility (Jefferson Lab) explores the history and uses of copper.