Christopher Columbus was an Italian explorer and colonist who completed four voyages across the Atlantic Ocean under the auspices of the Catholic Monarchs of Spain. He led the first European expeditions to the Caribbean, Central America, South America, initiating the permanent European colonization of the Americas. Columbus discovered the viable sailing route to the Americas, a continent, not known to the Old World. While what he thought he had discovered was a route to the Far East, he is credited with the opening of the Americas for conquest and settlement by Europeans. Columbus's early life is somewhat obscure, but scholars agree that he was born in the Republic of Genoa and spoke a dialect of Ligurian as his first language, he went to sea at a young age and travelled as far north as the British Isles and as far south as what is now Ghana. He married Portuguese noblewoman Filipa Moniz Perestrelo and was based in Lisbon for several years, but took a Spanish mistress. Though self-educated, Columbus was read in geography and history.
He formulated a plan to seek a western sea passage to the East Indies, hoping to profit from the lucrative spice trade. After years of lobbying, the Catholic Monarchs of Spain agreed to sponsor a journey west, in the name of the Crown of Castile. Columbus left Spain in August 1492 with three ships, after a stopover in the Canary Islands made landfall in the Americas on 12 October, his landing place was an island in the Bahamas, known by its native inhabitants as Guanahani. Columbus subsequently visited Cuba and Hispaniola, establishing a colony in what is now Haiti—the first European settlement in the Americas since the Norse colonies 500 years earlier, he arrived back in Spain in early 1493. Word of his discoveries soon spread throughout Europe. Columbus would make three further voyages to the New World, exploring the Lesser Antilles in 1493, Trinidad and the northern coast of South America in 1498, the eastern coast of Central America in 1502. Many of the names he gave to geographical features—particularly islands—are still in use.
He continued to seek a passage to the East Indies, the extent to which he was aware that the Americas were a wholly separate landmass is uncertain. Columbus's strained relationship with the Spanish crown and its appointed colonial administrators in America led to his arrest and removal from Hispaniola in 1500, to protracted litigation over the benefits that he and his heirs claimed were owed to them by the crown. Columbus's expeditions inaugurated a period of exploration and colonization that lasted for centuries, helping create the modern Western world; the transfers between the Old World and New World that followed his first voyage are known as the Columbian exchange, the period of human habitation in the Americas prior to his arrival is known as the Pre-Columbian era. Columbus's legacy continues to be debated, he was venerated in the centuries after his death, but public perceptions have changed as recent scholars have given attention to negative aspects of his life, such as his role in the extinction of the Taíno people, his promotion of slavery, allegations of tyranny towards Spanish colonists.
Many landmarks and institutions in the Western Hemisphere bear his name, including the country of Colombia. The name Christopher Columbus is the Anglicisation of the Latin Christophorus Columbus, his name in Ligurian is Cristoffa Corombo, in Italian Cristoforo Colombo, in Spanish is Cristóbal Colón, in Portuguese is Cristóvão Colombo. He was born before 31 October 1451 in the territory of the Republic of Genoa, though the exact location remains disputed, his father was Domenico Colombo, a middle-class wool weaver who worked both in Genoa and Savona and who owned a cheese stand at which young Christopher worked as a helper. His mother was Susanna Fontanarossa. Bartolomeo, Giovanni Pellegrino, Giacomo were his brothers. Bartolomeo worked in a cartography workshop in Lisbon for at least part of his adulthood, he had a sister named Bianchinetta. Columbus never wrote in his native language, presumed to have been a Genoese variety of Ligurian: his name in the 16th-century Genoese language would have been Cristoffa Corombo.
In one of his writings, he says he went to sea at the age of 10. In 1470, the Columbus family moved to Savona. In the same year, Christopher was on a Genoese ship hired in the service of René of Anjou to support his attempt to conquer the Kingdom of Naples; some modern historians have argued that he was not from Genoa but, from the Aragon region of Spain or from Portugal. These competing hypotheses have been discounted by mainstream scholars. In 1473, Columbus began his apprenticeship as business agent for the important Centurione, Di Negro and Spinola families of Genoa, he made a trip to Chios, an Aegean island ruled by Genoa. In May 1476, he took part in an armed convoy sent by Genoa to carry valuable cargo to northern Europe, he docked in Bristol and Galway, Ireland. In 1477, he was in Iceland. In the autumn of 1477, he sailed on a Portuguese ship from Galway to Lisbon, where he found his brother Bartolomeo, they continued trading for the Centurione family. Columbus based himself in Lisbon from 1477 to 1485.
He married Filipa Moniz Perestrelo, daughter of the Porto Santo governor and Portuguese nobleman of
Marriage called matrimony or wedlock, is a or ritually recognised union between spouses that establishes rights and obligations between those spouses, as well as between them and any resulting biological or adopted children and affinity. The definition of marriage varies around the world not only between cultures and between religions, but throughout the history of any given culture and religion, evolving to both expand and constrict in who and what is encompassed, but it is principally an institution in which interpersonal relationships sexual, are acknowledged or sanctioned. In some cultures, marriage is recommended or considered to be compulsory before pursuing any sexual activity; when defined broadly, marriage is considered a cultural universal. A marriage ceremony is known as a wedding. Individuals may marry for several reasons, including legal, libidinal, financial and religious purposes. Whom they marry may be influenced by gender determined rules of incest, prescriptive marriage rules, parental choice and individual desire.
In some areas of the world, arranged marriage, child marriage and sometimes forced marriage, may be practiced as a cultural tradition. Conversely, such practices may be outlawed and penalized in parts of the world out of concerns of the infringement of women's rights, or the infringement of children's rights, because of international law. Around the world in developed democracies, there has been a general trend towards ensuring equal rights within marriage for women and recognizing the marriages of interfaith and same-sex couples; these trends coincide with the broader human rights movement. Marriage can be recognized by a state, an organization, a religious authority, a tribal group, a local community, or peers, it is viewed as a contract. When a marriage is performed and carried out by a government institution in accordance with the marriage laws of the jurisdiction, without religious content, it is a civil marriage. Civil marriage recognizes and creates the rights and obligations intrinsic to matrimony before the state.
When a marriage is performed with religious content under the auspices of a religious institution it is a religious marriage. Religious marriage recognizes and creates the rights and obligations intrinsic to matrimony before that religion. Religious marriage is known variously as sacramental marriage in Catholicism, nikah in Islam, nissuin in Judaism, various other names in other faith traditions, each with their own constraints as to what constitutes, who can enter into, a valid religious marriage; some countries do not recognize locally performed religious marriage on its own, require a separate civil marriage for official purposes. Conversely, civil marriage does not exist in some countries governed by a religious legal system, such as Saudi Arabia, where marriages contracted abroad might not be recognized if they were contracted contrary to Saudi interpretations of Islamic religious law. In countries governed by a mixed secular-religious legal system, such as in Lebanon and Israel, locally performed civil marriage does not exist within the country, preventing interfaith and various other marriages contradicting religious laws from being entered into in the country, civil marriages performed abroad are recognized by the state if they conflict with religious laws.
The act of marriage creates normative or legal obligations between the individuals involved, any offspring they may produce or adopt. In terms of legal recognition, most sovereign states and other jurisdictions limit marriage to opposite-sex couples and a diminishing number of these permit polygyny, child marriages, forced marriages. In modern times, a growing number of countries developed democracies, have lifted bans on and have established legal recognition for the marriages of interfaith and same-sex couples; some cultures allow the dissolution of marriage through annulment. In some areas, child marriages and polygamy may occur in spite of national laws against the practice. Since the late twentieth century, major social changes in Western countries have led to changes in the demographics of marriage, with the age of first marriage increasing, fewer people marrying, more couples choosing to cohabit rather than marry. For example, the number of marriages in Europe decreased by 30% from 1975 to 2005.
In most cultures, married women had few rights of their own, being considered, along with the family's children, the property of the husband. In Europe, the United States, other places in the developed world, beginning in the late 19th century and lasting through the 21st century, marriage has undergone gradual legal changes, aimed at improving the rights of the wife; these changes included giving wives legal identities of their own, abolishing the right of husbands to physically discipline their wives, giving wives property rights, liberalizing divorce laws, providing wives with reproductive rights of their own, requiring a wife's consent when sexual relations occur. These changes have occurred in Western countries. In the 21st century, there continue to be controversies regarding the legal status of married women, legal acceptance of or leniency towards violence within marriage, traditional marriage customs such as dowry and bride price, for
Silver is a chemical element with symbol Ag and atomic number 47. A soft, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, reflectivity of any metal; the metal is found in the Earth's crust in the pure, free elemental form, as an alloy with gold and other metals, in minerals such as argentite and chlorargyrite. Most silver is produced as a byproduct of copper, gold and zinc refining. Silver has long been valued as a precious metal. Silver metal is used in many bullion coins, sometimes alongside gold: while it is more abundant than gold, it is much less abundant as a native metal, its purity is measured on a per-mille basis. As one of the seven metals of antiquity, silver has had an enduring role in most human cultures. Other than in currency and as an investment medium, silver is used in solar panels, water filtration, ornaments, high-value tableware and utensils, in electrical contacts and conductors, in specialized mirrors, window coatings, in catalysis of chemical reactions, as a colorant in stained glass and in specialised confectionery.
Its compounds are used in X-ray film. Dilute solutions of silver nitrate and other silver compounds are used as disinfectants and microbiocides, added to bandages and wound-dressings and other medical instruments. Silver is similar in its physical and chemical properties to its two vertical neighbours in group 11 of the periodic table and gold, its 47 electrons are arranged in the configuration 4d105s1 to copper and gold. This distinctive electron configuration, with a single electron in the highest occupied s subshell over a filled d subshell, accounts for many of the singular properties of metallic silver. Silver is an soft and malleable transition metal, though it is less malleable than gold. Silver crystallizes in a face-centered cubic lattice with bulk coordination number 12, where only the single 5s electron is delocalized to copper and gold. Unlike metals with incomplete d-shells, metallic bonds in silver are lacking a covalent character and are weak; this observation explains the low high ductility of single crystals of silver.
Silver has a brilliant white metallic luster that can take a high polish, and, so characteristic that the name of the metal itself has become a colour name. Unlike copper and gold, the energy required to excite an electron from the filled d band to the s-p conduction band in silver is large enough that it no longer corresponds to absorption in the visible region of the spectrum, but rather in the ultraviolet. Protected silver has greater optical reflectivity than aluminium at all wavelengths longer than ~450 nm. At wavelengths shorter than 450 nm, silver's reflectivity is inferior to that of aluminium and drops to zero near 310 nm. High electrical and thermal conductivity is common to the elements in group 11, because their single s electron is free and does not interact with the filled d subshell, as such interactions lower electron mobility; the electrical conductivity of silver is the greatest of all metals, greater than copper, but it is not used for this property because of the higher cost.
An exception is in radio-frequency engineering at VHF and higher frequencies where silver plating improves electrical conductivity because those currents tend to flow on the surface of conductors rather than through the interior. During World War II in the US, 13540 tons of silver were used in electromagnets for enriching uranium because of the wartime shortage of copper. Pure silver has the highest thermal conductivity of any metal, although the conductivity of carbon and superfluid helium-4 are higher. Silver has the lowest contact resistance of any metal. Silver forms alloys with copper and gold, as well as zinc. Zinc-silver alloys with low zinc concentration may be considered as face-centred cubic solid solutions of zinc in silver, as the structure of the silver is unchanged while the electron concentration rises as more zinc is added. Increasing the electron concentration further leads to body-centred cubic, complex cubic, hexagonal close-packed phases. Occurring silver is composed of two stable isotopes, 107Ag and 109Ag, with 107Ag being more abundant.
This equal abundance is rare in the periodic table. The atomic weight is 107.8682 u. Both isotopes of silver are produced in stars via the s-process, as well as in supernovas via the r-process. Twenty-eight radioisotopes have been characterized, the most stable being 105Ag with a half-life of 41.29 days, 111Ag with a half-life of 7.45 days, 112Ag with a half-life of 3.13 hours. Silver has numerous nuclear isomers, the most stable being 108mAg, 110mAg and 106mAg. All of the remaining radioactive isotopes have half-lives of less than an hour, the majority of these have half-lives of less than three minutes. Isotopes of silver range in relative atomic mass from 92.950 u
Fertility is the natural capability to produce offspring. As a measure, fertility rate is the number of offspring born per mating pair, individual or population. Fertility differs from fecundity, defined as the potential for reproduction. A lack of fertility is infertility. Human fertility depends on factors of nutrition, sexual behavior, culture, endocrinology, economics, way of life, emotions. In demographic contexts, fertility refers to the actual production of offspring, rather than the physical capability to produce, termed fecundity. While fertility can be measured, fecundity cannot be. Demographers measure the fertility rate in a variety of ways, which can be broadly broken into "period" measures and "cohort" measures. "Period" measures refer to a cross-section of the population in one year. "Cohort" data on the other hand, follows the same people over a period of decades. Both period and cohort measures are used. Crude birth rate - the number of live births in a given year per 1,000 people alive at the middle of that year.
One disadvantage of this indicator is. General fertility rate - the number of births in a year divided by the number of women aged 15–44, times 1000, it focuses on the potential mothers only, takes the age distribution into account. Child-Woman Ratio - the ratio of the number of children under 5 to the number of women 15–49, times 1000, it is useful in historical data as it does not require counting births. This measure is a hybrid, because it involves deaths as well as births. Coale's Index of Fertility - a special device used in historical research Total fertility rate - the total number of children a woman would bear during her lifetime if she were to experience the prevailing age-specific fertility rates of women. TFR equals the sum for all age groups of 5 times each ASFR rate. Gross Reproduction Rate - the number of girl babies a synthetic cohort will have, it assumes that all of the baby girls will grow up and live to at least age 50. Net Reproduction Rate - the NRR starts with the GRR and adds the realistic assumption that some of the women will die before age 49.
NRR is always lower than GRR, but in countries where mortality is low all the baby girls grow up to be potential mothers, the NRR is the same as GRR. In countries with high mortality, NRR can be as low as 70% of GRR; when NRR = 1.0, each generation of 1000 baby girls grows up and gives birth to 1000 girls. When NRR is less than one, each generation is smaller than the previous one; when NRR is greater than 1 each generation is larger than the one before. NRR is a measure of the long-term future potential for growth, but it is different from the current population growth rate. A parent's number of children correlates with the number of children that each person in the next generation will have. Factors associated with increased fertility include religiosity, intention to have children, maternal support. Factors associated with decreased fertility include wealth, female labor participation, urban residence, increased female age and increased male age; the "Three-step Analysis" of the fertility process was introduced by Kingsley Davis and Judith Blake in 1956 and makes use of three proximate determinants: The economic analysis of fertility is part of household economics, a field that has grown out of the New Home Economics.
Influential economic analyses of fertility include Becker and Easterlin. The latter developed. Bongaarts proposed a model where the total fertility rate of a population can be calculated from four proximate determinants and the total fecundity; the index of marriage, the index of contraception, the index of induced abortion and the index of postpartum infecundability. These indices range from 0 to 1; the higher the index, the higher it will make the TFR, for example a population where there are no induced abortions would have a Ca of 1, but a country where everybody used infallible contraception would have a Cc of 0. TFR = TF × Cm × Ci × Ca × Cc These four indices can be used to calculate the total marital fertility and the total natural fertility. TFR = TMFR × Cm TMFR = TN × Cc × Ca TN = TF × Ci Intercourse The first step is sexual intercourse, an examination of the average age at first intercourse, the average frequency outside marriage, the average frequency inside. Conception Certain physical conditions may make it impossible for a woman to conceive.
This is called "involuntary infecundity." If the woman has a condition making it possible, but unlikely to conceive, this is termed "subfecundity." Venereal diseases are common causes. Nutrition is a factor as well: women with less than 20% body fat may be subfecund, a factor of concern for athletes and people susceptible to anorexia. Demographer Ruth Frisch has argued that "It takes 50,000 calories to make a baby". There is subfecundity in the weeks following childbirth, this can be prolonged for a year or more through breastfeeding. A furious political debate raged in the 1980s over the ethics of baby food companies marketing infant f
Gold is a chemical element with symbol Au and atomic number 79, making it one of the higher atomic number elements that occur naturally. In its purest form, it is a bright reddish yellow, soft and ductile metal. Chemically, gold is a group 11 element, it is solid under standard conditions. Gold occurs in free elemental form, as nuggets or grains, in rocks, in veins, in alluvial deposits, it occurs in a solid solution series with the native element silver and naturally alloyed with copper and palladium. Less it occurs in minerals as gold compounds with tellurium. Gold is resistant to most acids, though it does dissolve in aqua regia, a mixture of nitric acid and hydrochloric acid, which forms a soluble tetrachloroaurate anion. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to refine gold and to confirm the presence of gold in metallic objects, giving rise to the term acid test. Gold dissolves in alkaline solutions of cyanide, which are used in mining and electroplating.
Gold dissolves in mercury, forming amalgam alloys. A rare element, gold is a precious metal, used for coinage and other arts throughout recorded history. In the past, a gold standard was implemented as a monetary policy, but gold coins ceased to be minted as a circulating currency in the 1930s, the world gold standard was abandoned for a fiat currency system after 1971. A total of 186,700 tonnes of gold exists above ground, as of 2015; the world consumption of new gold produced is about 50% in jewelry, 40% in investments, 10% in industry. Gold's high malleability, resistance to corrosion and most other chemical reactions, conductivity of electricity have led to its continued use in corrosion resistant electrical connectors in all types of computerized devices. Gold is used in infrared shielding, colored-glass production, gold leafing, tooth restoration. Certain gold salts are still used as anti-inflammatories in medicine; as of 2017, the world's largest gold producer by far was China with 440 tonnes per year.
Gold is the most malleable of all metals. It can be drawn into a monoatomic wire, stretched about twice before it breaks; such nanowires distort via formation and migration of dislocations and crystal twins without noticeable hardening. A single gram of gold can be beaten into a sheet of 1 square meter, an avoirdupois ounce into 300 square feet. Gold leaf can be beaten thin enough to become semi-transparent; the transmitted light appears greenish blue, because gold reflects yellow and red. Such semi-transparent sheets strongly reflect infrared light, making them useful as infrared shields in visors of heat-resistant suits, in sun-visors for spacesuits. Gold is a good conductor of electricity. Gold has a density of 19.3 g/cm3 identical to that of tungsten at 19.25 g/cm3. By comparison, the density of lead is 11.34 g/cm3, that of the densest element, osmium, is 22.588±0.015 g/cm3. Whereas most metals are gray or silvery white, gold is reddish-yellow; this color is determined by the frequency of plasma oscillations among the metal's valence electrons, in the ultraviolet range for most metals but in the visible range for gold due to relativistic effects affecting the orbitals around gold atoms.
Similar effects impart a golden hue to metallic caesium. Common colored gold alloys include the distinctive eighteen-karat rose gold created by the addition of copper. Alloys containing palladium or nickel are important in commercial jewelry as these produce white gold alloys. Fourteen-karat gold-copper alloy is nearly identical in color to certain bronze alloys, both may be used to produce police and other badges. White gold alloys can be made with nickel. Fourteen- and eighteen-karat gold alloys with silver alone appear greenish-yellow and are referred to as green gold. Blue gold can be made by alloying with iron, purple gold can be made by alloying with aluminium. Less addition of manganese, aluminium and other elements can produce more unusual colors of gold for various applications. Colloidal gold, used by electron-microscopists, is red. Gold has only one stable isotope, 197Au, its only occurring isotope, so gold is both a mononuclidic and monoisotopic element. Thirty-six radioisotopes have been synthesized, ranging in atomic mass from 169 to 205.
The most stable of these is 195Au with a half-life of 186.1 days. The least stable is 171Au. Most of gold's radioisotopes with atomic masses below 197 decay by some combination of proton emission, α decay, β+ decay; the exceptions are 195Au, which decays by electron capture, 196Au, which decays most by electron capture with a minor β− decay path. All of gold's radioisotopes with atomic masses above 197 decay by β− decay. At least 32 nuclear isomers have been characterized, ranging in atomic mass from 170 to 200. Within that range, only 178Au, 180Au, 181Au, 182Au, 188Au do not have isomers. Gold's most stable isomer is 198m2Au with a half-life of 2.27 days. Gold's least stable isomer is 177m2Au with a half-life of only 7 ns. 184m1Au has three decay paths: β+ decay, isomeric
An alliance is a relationship among people, groups, or states that have joined together for mutual benefit or to achieve some common purpose, whether or not explicit agreement has been worked out among them. Members of an alliance are called allies. Alliances form in many settings, including political alliances, military alliances, business alliances; when the term is used in the context of war or armed struggle, such associations may be called allied powers when discussing World War I or World War II. A formal military alliance is not required for being perceived as an ally—co-belligerence, fighting alongside someone, is enough. According to this usage, allies become so not when concluding an alliance treaty but when struck by war; when spelled with a capital "A", "Allies" denotes the countries who fought together against the Central Powers in World War I, or those who fought against the Axis Powers in World War II. The term has been used by the United States Army to describe the countries that gave assistance to South Vietnam during the Vietnam War.
More the term "Allied forces" has been used to describe the coalition of the Gulf War, as opposed to forces the Multi-National Forces in Iraq which are referred to as "Coalition forces" or, as by the George W. Bush administration, "the coalition of the willing"; the Allied Powers in World War I were the United Kingdom, the Russian Empire, Serbia and Japan, joined by Italy, Romania, the United States and Brazil. Some, such as the Russian Empire, withdrew from the war before the armistice due to revolution or defeat. Scholars are divided as to the impact of alliances. Several studies find. One study questions these findings, showing that alliance commitments deterred conflict in the prenuclear era but has no statistically meaningful impact on war in the postnuclear era. Another study finds that while alliance commitments deter conflict between sides with a recent history of conflict, alliances tend to provoke conflicts between states without such a history. A 2000 study in the Journal of Conflict Resolution found that allies fulfill their alliance commitments 75% of the time.
Most research suggests. A 2004 study did however question. A 2018 study updated and extended the data from the 2000 Journal of Conflict Resolution study and found that allies only fulfill their commitments about 50% of the time from 1816 to 2003. According to the study, "States honored their alliance commitments 66% of the time prior to 1945 but the compliance rate drops to 22% from 1945 to 2003. Moreover, the rates of fulfillment for defense pacts and nonaggression pacts are lower than offensive alliances and neutrality agreements." According to a 2017 poll by WIN/GIA, the United States was the most preferred ally internationally. Russia and China, who preferred one another, both trailed America globally. Four countries, Greece and Turkey, preferred Russia, despite being members of NATO. In Pakistan, 72% of respondents preferred ties to China, the largest margin of any country surveyed, while 46% of Bangladesh preferred India. A total of 22 countries indicated a preference for the United Kingdom at a rate of 10% or more, but the United States was the only country to prefer the Britain over any other, at a rate of 43%.
Five counties preferred France at a rate of 10% or more, led by Belgium at a rate of 25%. A single country, Iraq expressed no preference, while three other countries, Lebanon and Slovenia, expressed no preference at a rate of 11% or more, although at a smaller rate than their preference for Russia on the part of Lebanon and Slovenia, China on the part of Palestine. Kosovo reported the most unified opinion, preferring the United States at a rate of 92%, while Russia's most unified supporters were Mongolia and Serbia. In total, 21 countries expressed a preference for America at a rate of 50% or more. Neutral country Allies of World War I Allies of World War II Airline alliance Business alliance Military alliance Political alliance Therapeutic alliance, the relationship between a healthcare professional and a client Beer, Francis A.. Alliances: Latent War Communities in the Contemporary World. New York: Holt and Winston; the dictionary definition of ally at Wiktionary "Alliance". Encyclopædia Britannica.
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Copper is a chemical element with symbol Cu and atomic number 29. It is a soft and ductile metal with high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity, as a building material, as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, constantan used in strain gauges and thermocouples for temperature measurement. Copper is one of the few metals; this led to early human use in several regions, from c. 8000 BC. Thousands of years it was the first metal to be smelted from sulfide ores, c. 5000 BC, the first metal to be cast into a shape in a mold, c. 4000 BC and the first metal to be purposefully alloyed with another metal, tin, to create bronze, c. 3500 BC. In the Roman era, copper was principally mined on Cyprus, the origin of the name of the metal, from aes сyprium corrupted to сuprum, from which the words derived and copper, first used around 1530.
The encountered compounds are copper salts, which impart blue or green colors to such minerals as azurite and turquoise, have been used and as pigments. Copper used in buildings for roofing, oxidizes to form a green verdigris. Copper is sometimes used in decorative art, both in its elemental metal form and in compounds as pigments. Copper compounds are used as bacteriostatic agents and wood preservatives. Copper is essential to all living organisms as a trace dietary mineral because it is a key constituent of the respiratory enzyme complex cytochrome c oxidase. In molluscs and crustaceans, copper is a constituent of the blood pigment hemocyanin, replaced by the iron-complexed hemoglobin in fish and other vertebrates. In humans, copper is found in the liver and bone; the adult body contains between 2.1 mg of copper per kilogram of body weight. Copper and gold are in group 11 of the periodic table; the filled d-shells in these elements contribute little to interatomic interactions, which are dominated by the s-electrons through metallic bonds.
Unlike metals with incomplete d-shells, metallic bonds in copper are lacking a covalent character and are weak. This observation explains the low high ductility of single crystals of copper. At the macroscopic scale, introduction of extended defects to the crystal lattice, such as grain boundaries, hinders flow of the material under applied stress, thereby increasing its hardness. For this reason, copper is supplied in a fine-grained polycrystalline form, which has greater strength than monocrystalline forms; the softness of copper explains its high electrical conductivity and high thermal conductivity, second highest among pure metals at room temperature. This is because the resistivity to electron transport in metals at room temperature originates from scattering of electrons on thermal vibrations of the lattice, which are weak in a soft metal; the maximum permissible current density of copper in open air is 3.1×106 A/m2 of cross-sectional area, above which it begins to heat excessively. Copper is one of a few metallic elements with a natural color other than silver.
Pure copper acquires a reddish tarnish when exposed to air. The characteristic color of copper results from the electronic transitions between the filled 3d and half-empty 4s atomic shells – the energy difference between these shells corresponds to orange light; as with other metals, if copper is put in contact with another metal, galvanic corrosion will occur. Copper does not react with water, but it does react with atmospheric oxygen to form a layer of brown-black copper oxide which, unlike the rust that forms on iron in moist air, protects the underlying metal from further corrosion. A green layer of verdigris can be seen on old copper structures, such as the roofing of many older buildings and the Statue of Liberty. Copper tarnishes when exposed to some sulfur compounds, with which it reacts to form various copper sulfides. There are 29 isotopes of copper. 63Cu and 65Cu are stable, with 63Cu comprising 69% of occurring copper. The other isotopes are radioactive, with the most stable being 67Cu with a half-life of 61.83 hours.
Seven metastable isotopes have been characterized. Isotopes with a mass number above 64 decay by β−, whereas those with a mass number below 64 decay by β+. 64Cu, which has a half-life of 12.7 hours, decays both ways.62Cu and 64Cu have significant applications. 62Cu is used in 62Cu-PTSM as a radioactive tracer for positron emission tomography. Copper is produced in massive stars and is present in the Earth's crust in a proportion of about 50 parts per million. In nature, copper occurs in a variety of minerals, including native copper, copper sulfides such as chalcopyrite, digenite and chalcocite, copper sulfosalts such as tetrahedite-tennantite, enargite, copper carbonates such as azurite and malachite, as copper or copper oxides such as cuprite and tenorite, respectively; the largest mass of elemental copper discovered weighed 420 tonnes and was found in 1857 on the Keweenaw Peninsula in Michigan, US. Native copper is a polycrystal