There are two main theories about how gold is originally formed, both involving stars. One involves the explosion of supernova stars and the resulting nuclear fusion creating atoms of gold, and the other, the collision of neutron stars that results in a gamma-ray burst, one of the most powerful explosions possible. In August , the presence of heavier elements, including gold, was detected using gravitational wave detectors during the first observation of the collision of two neutron stars.
What these two events have in common is the presence of nuclear energy, which is required to combine lighter atoms into heavier ones. Where is gold found? In its natural form, it is found deep in the layers of the earth where it is transported by water, molten lava and volcanic eruptions, and earthquakes.
Geologists have found gold in rocks as old as 4. The Witwatersrand, one of the most gold-rich mining areas in the world, is located in a km radius crater in southern Africa, thought to have been caused by a meteor strike over 2 billion years ago.
This theory reinforces the idea that gold was brought to earth from the cosmos by asteroids. Gold is also found in our oceans. All the water in the seas and oceans of earth is believed to hold a cumulative total of between 10 and 20 million tons of gold , mostly diluted in water at a tiny concentration level. It can also be made synthetically, but the process requires nuclear reactions that make it prohibitively expensive and impractical to produce and sell for its current uses.
How is gold processed? Gold can be recovered from ore in a few ways. Metals are often extracted from the Earth by means of mining, resulting in ores that are relatively rich sources of the requisite elements. Ore is located by prospecting techniques, followed by the exploration and examination of deposits. Mineral sources are generally divided into surface mines, which are mined by excavation using heavy equipment, and subsurface mines.
Mining : Chuquicamata, Chile, is the site of the largest circumference and second deepest open pit copper mine in the world. After the ore is mined, the metals must be extracted, usually by chemical or electrolytic reduction. Pyrometallurgy uses high temperatures to convert ore into raw metals, while hydrometallurgy employs aqueous chemistry for the same purpose.
The methods used depend on the metal and their contaminants. When a metal ore is an ionic compound of that metal and a non-metal, the ore must usually be smelted or heated with a reducing agent to extract the pure metal. Many common metals, such as iron, are smelted using carbon as a reducing agent. Some metals, such as aluminium and sodium, have no commercially practical reducing agent, and are extracted using electrolysis instead.
Sulfide ores are not reduced directly to the metal, but are roasted in air to convert them to oxides. A metal can refer to an element, compound, or alloy that is a good conductor of both electricity and heat.
Example metals include gold, sodium, copper, iron, and many other elements. Metals are usually malleable, ductile, and shiny. Metals typically consist of close-packed atoms, meaning that the atoms are arranged like closely packed spheres. In a metal, atoms readily lose electrons to form positive ions cations. Those ions are surrounded by de-localized electrons, which are responsible for the conductivity. The solid produced is held together by electrostatic interactions between the ions and the electron cloud, which are called metallic bonds.
Metals are shiny and lustrous with a high density. They have very high melting and boiling points because metallic bonding is very strong, so the atoms are reluctant to break apart into a liquid or gas. Sodium Metal : Sodium metal is soft enough to be cut with a plastic knife.
Metals in general are conductive, with high electrical conductivity and high thermal conductivity. Typically they are malleable and ductile, deforming under stress without cleaving.
The electrical and thermal conductivities of metals originate from the fact that their outer electrons are delocalized. This means the electrons are not locked into any one atom but can move freely throughout the metal. Metals can be viewed as a collection of atoms embedded in a sea of electrons, which are highly mobile.
This is very instrumental in the conductivity of the metal. Metals are usually inclined to form cations through electron loss.
An example is the reaction with oxygen in the air to form oxides over various timescales iron rusts over years, while potassium burns in seconds. The transition metals such as iron, copper, zinc, and nickel are slower to oxidize because they form a passivating layer of oxide that protects the interior. Others, like palladium, platinum, and gold, do not react with the atmosphere at all.
Some metals form a barrier layer of oxide on their surface, which cannot be penetrated by further oxygen molecules. As a result, they retain their shiny appearance and good conductivity for many decades like aluminium, magnesium, some steels, and titanium. Recall that in the periodic table, each row is called a period. The rows are aligned in such a way that the elements in each vertical column share certain characteristics.
Each of the columns of the periodic table is called a group. Chemists have long found it convenient to refer to the elements of different groups, and in some cases of spans of groups, by the names shown in the table. Trends in the periodic table : Families of the periodic table are often grouped by metallic properties. When two elements are joined in a chemical bond, the element that attracts the shared electrons more strongly has more electronegativity.
Elements with low electronegativity tend to have more metallic properties. So, the metallic properties of elements tends to decrease across a period and increase down a group. The fact that the metallic elements are found on the left side of the periodic table offers an important clue to the nature of how they bond together to form solids. These elements all possess low electronegativities and readily form positive ions.
Metals tend to form positive ions, and like charges repel, so how do metal atoms stay bonded together in a solid? In effect, the electropositive nature of the metallic atoms allows their valence electrons to exist as a mobile fluid. This results in their high electrical conductivities.
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