Sulfuric acid known as vitriol, is a mineral acid composed of the elements sulfur and hydrogen, with molecular formula H2SO4. It is a colorless and syrupy liquid, soluble in water, in a reaction, exothermic, its corrosiveness can be ascribed to its strong acidic nature, and, if at a high concentration, its dehydrating and oxidizing properties. It is hygroscopic absorbing water vapor from the air. Upon contact, sulfuric acid can cause severe chemical burns and secondary thermal burns. Sulfuric acid is a important commodity chemical, a nation's sulfuric acid production is a good indicator of its industrial strength, it is produced with different methods, such as contact process, wet sulfuric acid process, lead chamber process and some other methods. Sulfuric acid is a key substance in the chemical industry, it is most used in fertilizer manufacture, but is important in mineral processing, oil refining, wastewater processing, chemical synthesis. It has a wide range of end applications including in domestic acidic drain cleaners, as an electrolyte in lead-acid batteries, in various cleaning agents.
Although nearly 100% sulfuric acid can be made, the subsequent loss of SO3 at the boiling point brings the concentration to 98.3% acid. The 98.3% grade is more stable in storage, is the usual form of what is described as "concentrated sulfuric acid". Other concentrations are used for different purposes; some common concentrations are: "Chamber acid" and "tower acid" were the two concentrations of sulfuric acid produced by the lead chamber process, chamber acid being the acid produced in the lead chamber itself and tower acid being the acid recovered from the bottom of the Glover tower. They are now obsolete as commercial concentrations of sulfuric acid, although they may be prepared in the laboratory from concentrated sulfuric acid if needed. In particular, "10M" sulfuric acid is prepared by adding 98% sulfuric acid to an equal volume of water, with good stirring: the temperature of the mixture can rise to 80 °C or higher. Sulfuric acid reacts with its anhydride, SO3, to form H2S2O7, called pyrosulfuric acid, fuming sulfuric acid, Disulfuric acid or oleum or, less Nordhausen acid.
Concentrations of oleum are either expressed in terms of % SO3 or as % H2SO4. Pure H2S2O7 is a solid with melting point of 36 °C. Pure sulfuric acid has a vapor pressure of <0.001 mmHg at 25 °C and 1 mmHg at 145.8 °C, 98% sulfuric acid has a <1 mmHg vapor pressure at 40 °C. Pure sulfuric acid is a viscous clear liquid, like oil, this explains the old name of the acid. Commercial sulfuric acid is sold in several different purity grades. Technical grade H2SO4 is impure and colored, but is suitable for making fertilizer. Pure grades, such as United States Pharmacopeia grade, are used for making pharmaceuticals and dyestuffs. Analytical grades are available. Nine hydrates are known, but four of them were confirmed to be tetrahydrate and octahydrate. Anhydrous H2SO4 is a polar liquid, having a dielectric constant of around 100, it has a high electrical conductivity, caused by dissociation through protonating itself, a process known as autoprotolysis. 2 H2SO4 ⇌ H3SO+4 + HSO−4The equilibrium constant for the autoprotolysis is Kap = = 2.7×10−4The comparable equilibrium constant for water, Kw is 10−14, a factor of 1010 smaller.
In spite of the viscosity of the acid, the effective conductivities of the H3SO+4 and HSO−4 ions are high due to an intramolecular proton-switch mechanism, making sulfuric acid a good conductor of electricity. It is an excellent solvent for many reactions; because the hydration reaction of sulfuric acid is exothermic, dilution should always be performed by adding the acid to the water rather than the water to the acid. Because the reaction is in an equilibrium that favors the rapid protonation of water, addition of acid to the water ensures that the acid is the limiting reagent; this reaction is best thought of as the formation of hydronium ions: H2SO4 + H2O → H3O+ + HSO−4 Ka1 = 2.4×106 HSO−4 + H2O → H3O+ + SO2−4 Ka2 = 1.0×10−2 HSO−4 is the bisulfate anion and SO2−4 is the sulfate anion. Ka1 and Ka2 are the acid dissociation constants; because the hydration of sulfuric acid is thermodynamically favorable and the affinity of it for water is sufficiently strong, sulfuric acid is an excellent dehydrating agent.
Concentrated sulfuric acid has a powerful dehydrating property, removing water from other chemical compounds including sugar and other carbohydrates and producing carbon and steam. In the laboratory, this is demonstrated by mixing table sugar into sulfuric acid; the sugar changes from white to dark brown and to black as carbon is formed. A rigid column of black, porous carbon will emerge as well; the carbon will smell of caramel due to the heat generated. C 12 H 22 O 11 ⏞ sucrose → H 2 SO 4 12 C + 11 H 2
Direct current is the unidirectional flow of electric charge. A battery is a good example of a DC power supply. Direct current may flow in a conductor such as a wire, but can flow through semiconductors, insulators, or through a vacuum as in electron or ion beams; the electric current flows in a constant direction, distinguishing it from alternating current. A term used for this type of current was galvanic current; the abbreviations AC and DC are used to mean alternating and direct, as when they modify current or voltage. Direct current may be obtained from an alternating current supply by use of a rectifier, which contains electronic elements or electromechanical elements that allow current to flow only in one direction. Direct current may be converted into alternating current with a motor-generator set. Direct current is used as a power supply for electronic systems. Large quantities of direct-current power are used in production of aluminum and other electrochemical processes, it is used for some railways in urban areas.
High-voltage direct current is used to transmit large amounts of power from remote generation sites or to interconnect alternating current power grids. Direct current was produced in 1800 by Italian physicist Alessandro Volta's battery, his Voltaic pile; the nature of how current flowed. French physicist André-Marie Ampère conjectured that current travelled in one direction from positive to negative; when French instrument maker Hippolyte Pixii built the first dynamo electric generator in 1832, he found that as the magnet used passed the loops of wire each half turn, it caused the flow of electricity to reverse, generating an alternating current. At Ampère's suggestion, Pixii added a commutator, a type of "switch" where contacts on the shaft work with "brush" contacts to produce direct current; the late 1870s and early 1880s saw electricity starting to be generated at power stations. These were set up to power arc lighting running on high voltage direct current or alternating current; this was followed by the wide spread use of low voltage direct current for indoor electric lighting in business and homes after inventor Thomas Edison launched his incandescent bulb based electric "utility" in 1882.
Because of the significant advantages of alternating current over direct current in using transformers to raise and lower voltages to allow much longer transmission distances, direct current was replaced over the next few decades by alternating current in power delivery. In the mid-1950s, high-voltage direct current transmission was developed, is now an option instead of long-distance high voltage alternating current systems. For long distance underseas cables, this DC option is the only technically feasible option. For applications requiring direct current, such as third rail power systems, alternating current is distributed to a substation, which utilizes a rectifier to convert the power to direct current; the term DC is used to refer to power systems that use only one polarity of voltage or current, to refer to the constant, zero-frequency, or varying local mean value of a voltage or current. For example, the voltage across a DC voltage source is constant as is the current through a DC current source.
The DC solution of an electric circuit is the solution where all currents are constant. It can be shown that any stationary voltage or current waveform can be decomposed into a sum of a DC component and a zero-mean time-varying component. Although DC stands for "direct current", DC refers to "constant polarity". Under this definition, DC voltages can vary in time, as seen in the raw output of a rectifier or the fluctuating voice signal on a telephone line; some forms of DC have no variations in voltage, but may still have variations in output power and current. A direct current circuit is an electrical circuit that consists of any combination of constant voltage sources, constant current sources, resistors. In this case, the circuit voltages and currents are independent of time. A particular circuit voltage or current does not depend on the past value of any circuit voltage or current; this implies that the system of equations that represent a DC circuit do not involve integrals or derivatives with respect to time.
If a capacitor or inductor is added to a DC circuit, the resulting circuit is not speaking, a DC circuit. However, most such circuits have a DC solution; this solution gives the circuit currents when the circuit is in DC steady state. Such a circuit is represented by a system of differential equations; the solution to these equations contain a time varying or transient part as well as constant or steady state part. It is this steady state part, the DC solution. There are some circuits. Two simple examples are a constant current source connected to a capacitor and a constant voltage source connected to an inductor. In electronics, it is common to refer to a circuit, powered by a DC voltage source such as a battery or the output of a DC power supply as a DC circuit though what is meant is that the circuit is DC powered. DC is found in many extra-low voltage applications and some low-voltage applications where these are powered by batteries or solar power systems. Most electronic circuits require a DC power supply.
Domestic DC installations have differ
A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic CCD for Cathode Current Departs. A conventional current describes the direction. Electrons have a negative electrical charge, so the movement of electrons is opposite to that of the conventional current flow; the mnemonic cathode current departs means that electrons flow into the device's cathode from the external circuit. The electrode through which conventional current flows the other way, into the device, is termed an anode. Conventional current flow is from cathode to anode outside of the cell or device, regardless of the cell or device type and operating mode. Cathode polarity with respect to the anode can be positive or negative depending on how the device is being operated. Although positively charged cations always move towards the cathode and negatively charged anions move away from it, cathode polarity depends on the device type, can vary according to the operating mode.
In a device which absorbs energy of charge, the cathode is negative, in a device which provides energy, the cathode is positive: A battery or galvanic cell in use has a cathode, the positive terminal since, where the current flows out of the device. This outward current is carried internally by positive ions moving from the electrolyte to the positive cathode, it is continued externally by electrons moving into the battery which constitutes positive current flowing outwards. For example, the Daniell galvanic cell's copper electrode is the cathode. A battery, recharging or an electrolytic cell performing electrolysis has its cathode as the negative terminal, from which current exits the device and returns to the external generator as charge enters the battery/ cell. For example, reversing the current direction in a Daniell galvanic cell converts it into an electrolytic cell where the copper electrode is the positive terminal and the anode. In a diode, the cathode is the negative terminal at the pointed end of the arrow symbol, where current flows out of the device.
Note: electrode naming for diodes is always based on the direction of the forward current for types such as Zener diodes or solar cells where the current of interest is the reverse current. In vacuum tubes it is the negative terminal where electrons enter the device from the external circuit and proceed into the tube's near-vacuum, constituting a positive current flowing out of the device; the word was coined in 1834 from the Greek κάθοδος,'descent' or'way down', by William Whewell, consulted by Michael Faraday over some new names needed to complete a paper on the discovered process of electrolysis. In that paper Faraday explained that when an electrolytic cell is oriented so that electric current traverses the "decomposing body" in a direction "from East to West, or, which will strengthen this help to the memory, that in which the sun appears to move", the cathode is where the current leaves the electrolyte, on the West side: "kata downwards, `odos a way; the use of'West' to mean the'out' direction may appear unnecessarily contrived.
As related in the first reference cited above, Faraday had used the more straightforward term "exode". His motivation for changing it to something meaning'the West electrode' was to make it immune to a possible change in the direction convention for current, whose exact nature was not known at the time; the reference he used to this effect was the Earth's magnetic field direction, which at that time was believed to be invariant. He fundamentally defined his arbitrary orientation for the cell as being that in which the internal current would run parallel to and in the same direction as a hypothetical magnetizing current loop around the local line of latitude which would induce a magnetic dipole field oriented like the Earth's; this made the internal current East to West as mentioned, but in the event of a convention change it would have become West to East, so that the West electrode would not have been the'way out' any more. Therefore, "exode" would have become inappropriate, whereas "cathode" meaning'West electrode' would have remained correct with respect to the unchanged direction of the actual phenomenon underlying the current unknown but, he thought, unambiguously defined by the magnetic reference.
In retrospect the name change was unfortunate, not only because the Greek roots alone do not reveal the cathode's function any more, but more because, as we now know, the Earth's magnetic field direction on which the "cathode" term is based is subject to reversals whereas the current direction convention on which the "exode" term was based has no reason to change in the future. Since the discovery of the electron, an easier to remember, more durably technically correct, etymology has been suggested: cathode, from the Greek kathodos,'way down','the way into the cell for electrons'. In chemistry, a cathode is the electrode of an electrochemical cell.
An electrolytic cell is an electrochemical cell that drives a non-spontaneous redox reaction through the application of electrical energy. They are used to decompose chemical compounds, in a process called electrolysis—the Greek word lysis means to break up. Important examples of electrolysis are the decomposition of water into hydrogen and oxygen, bauxite into aluminium and other chemicals. Electroplating is done using an electrolytic cell. Electrolysis is a technique. An electrolytic cell has three component parts: two electrodes; the electrolyte is a solution of water or other solvents in which ions are dissolved. Molten salts such as sodium chloride are electrolytes; when driven by an external voltage applied to the electrodes, the ions in the electrolyte are attracted to an electrode with the opposite charge, where charge-transferring reactions can take place. Only with an external electrical potential of correct polarity and sufficient magnitude can an electrolytic cell decompose a stable, or inert chemical compound in the solution.
The electrical energy provided can produce a chemical reaction which would not occur spontaneously otherwise. A galvanic cell can be considered an electrolytic cell acting in reverse. While electrolytic cells convert electrical energy into chemical energy, galvanic cells convert chemical energy into electrical energy. Galvanic cells are used in batteries. Michael Faraday defined the cathode of a cell as the electrode to which cations flow within the cell, to be reduced by reacting with electrons from that electrode, he defined the anode as the electrode to which anions flow within the cell, to be oxidized by depositing electrons on the electrode. To an external wire connected to the electrodes of a Galvanic cell, forming an electric circuit, the cathode is positive and the anode is negative, thus positive electric current flows from the cathode to the anode through the external circuit in the case of a Galvanic cell. Consider two voltaic cells of unequal voltage. Mark the positive and negative electrodes of each one as P and N, respectively.
Place them in a circuit with P near P and N near N, so the cells will tend to drive current in opposite directions. The cell with the larger voltage is discharged, making it a galvanic cell, so P is the cathode and N is the anode as described above. But, the cell with the smaller voltage charges, making it an electrolytic cell. In the electrolytic cell, negative ions are driven towards P and positive ions towards N. Thus, the P electrode of the electrolytic cell meets the definition of anode while the electrolytic cell is being charged; the N electrode of the electrolytic cell is the cathode while the electrolytic cell is being charged. As noted, water when ions are added, can be electrolyzed; when driven by an external source of voltage, H+ ions flow to the cathode to combine with electrons to produce hydrogen gas in a reduction reaction. OH− ions flow to the anode to release electrons and an H+ ion to produce oxygen gas in an oxidation reaction. In molten sodium chloride, when a current is passed through the salt the anode oxidizes chloride ions to chlorine gas, releasing electrons to the anode.
The cathode reduces sodium ions, which accept electrons from the cathode and deposits on the cathode as sodium metal. NaCl dissolved in water can be electrolyzed; the anode oxidizes chloride ions, Cl2 gas is produced. However, at the cathode, instead of sodium ions being reduced to sodium metal, water molecules are reduced to hydroxide ions and hydrogen gas; the overall result of the electrolysis is the production of chlorine gas and aqueous sodium hydroxide solution. Commercially, electrolytic cells are used in electrorefining and electrowinning of several non-ferrous metals. All high-purity aluminium, copper and lead is produced industrially in electrolytic cells. Concentration cell Electrochemical cell Galvanic cell
Plating is a surface covering in which a metal is deposited on a conductive surface. Plating has been done for hundreds of years. Plating is used to decorate objects, for corrosion inhibition, to improve solderability, to harden, to improve wearability, to reduce friction, to improve paint adhesion, to alter conductivity, to improve IR reflectivity, for radiation shielding, for other purposes. Jewelry uses plating to give a silver or gold finish. Thin-film deposition has plated objects as small as an atom, therefore plating finds uses in nanotechnology. There are several plating methods, many variations. In one method, a solid surface is covered with a metal sheet, heat and pressure are applied to fuse them. Other plating techniques include electroplating, vapor deposition under vacuum and sputter deposition. Plating refers to using liquids. Metallizing refers to coating metal on non-metallic objects. In electroplating, an ionic metal is supplied with electrons to form a non-ionic coating on a substrate.
A common system involves a chemical solution with the ionic form of the metal, an anode which may consist of the metal being plated or an insoluble anode, a cathode where electrons are supplied to produce a film of non-ionic metal. Electroless plating known as chemical or auto-catalytic plating, is a non-galvanic plating method that involves several simultaneous reactions in an aqueous solution, which occur without the use of external electrical power; the reaction is accomplished when hydrogen is released by a reducing agent sodium hypophosphite or thiourea, oxidized, thus producing a negative charge on the surface of the part. The most common electroless plating method is electroless nickel plating, although silver and copper layers can be applied in this manner, as in the technique of Angel gilding. Gold plating is a method of depositing a thin layer of gold on the surface of glass or metal, most copper or silver. Gold plating is used in electronics, to provide a corrosion-resistant electrically conductive layer on copper in electrical connectors and printed circuit boards.
With direct gold-on-copper plating, the copper atoms have the tendency to diffuse through the gold layer, causing tarnishing of its surface and formation of an oxide/sulfide layer. Therefore, a layer of a suitable barrier metal nickel, has to be deposited on the copper substrate, forming a copper-nickel-gold sandwich. Metals and glass may be coated with gold for ornamental purposes, using a number of different processes referred to as gilding. Sapphires and carbon fiber are some other materials that are able to be plated using advance plating techniques; the substrates that can be used are limitless. This section is about the method of adding a thin layer of silver to an object. For the Manhattan Project operation, see Silverplate. Silver plating has been used since the 18th century to provide cheaper versions of household items that would otherwise be made of solid silver, including cutlery, vessels of various kinds, candlesticks. In the UK the assay offices, silver dealers and collectors, use the term "silver plate" for items made from solid silver, derived long before silver plating was invented from the Spanish word for silver "plata", seizures of silver from Spanish ships carrying silver from America being a large source of silver at the time.
This can cause confusion. In the UK it is illegal to describe silver-plated items as "silver", it is not illegal to describe silver-plated items as "silver plate", although this is grammatically incorrect, should be avoided to prevent confusion. The earliest form of silver plating was Sheffield Plate, where thin sheets of silver are fused to a layer or core of base metal, but in the 19th century new methods of production were introduced. Britannia metal is an alloy of tin and copper developed as a base metal for plating with silver. Another method that can be used to apply a thin layer of silver to objects such as glass, is to place Tollens' reagent in a glass, add glucose/dextrose, shake the bottle to promote the reaction. AgNO3 + KOH → AgOH + KNO3AgOH + 2 NH3 → + + − + + − + aldehyde → Ag + 2 NH3 + H2OFor applications in electronics, silver is sometimes used for plating copper, as its electrical resistance is lower. Variable capacitors are considered of the highest quality. Silver-plated, or solid silver cables, are prized in audiophile applications.
Care should be used for parts exposed to high humidity environments because in such environments, when the silver layer is porous or contains cracks, the underlying copper undergoes rapid galvanic corrosion, flaking off the plating and exposing the copper itself. Silver plated copper maintained in a moisture-free environment will not undergo this type of corrosion. Copper plating is the process of electrolytically forming a layer of copper on the surface of an item. Rhodium plating is used on white gold, silver or copper and its alloys. A barrier layer of nickel is deposited on silver first, though in this case
An anode is an electrode through which the conventional current enters into a polarized electrical device. This contrasts with a cathode, an electrode through which conventional current leaves an electrical device. A common mnemonic is ACID for "anode current into device"; the direction of conventional current in a circuit is opposite to the direction of electron flow, so electrons flow out the anode into the outside circuit. In a galvanic cell, the anode is the electrode. An anode is the wire or plate having excess positive charge. Anions will tend to move towards the anode; the terms anode and cathode are not defined by the voltage polarity of electrodes but the direction of current through the electrode. An anode is an electrode through which conventional current flows into the device from the external circuit, while a cathode is an electrode through which conventional current flows out of the device. If the current through the electrodes reverses direction, as occurs for example in a rechargeable battery when it is being charged, the naming of the electrodes as anode and cathode is reversed.
Conventional current depends not only on the direction the charge carriers move, but the carriers' electric charge. The currents outside the device are carried by electrons in a metal conductor. Since electrons have a negative charge, the direction of electron flow is opposite to the direction of conventional current. Electrons leave the device through the anode and enter the device through the cathode; the definition of anode and cathode is different for electrical devices such as diodes and vacuum tubes where the electrode naming is fixed and does not depend on the actual charge flow. These devices allow substantial current flow in one direction but negligible current in the other direction; therefore the electrodes are named based on the direction of this "forward" current. In a diode the anode is the terminal through which current enters and the cathode is the terminal through which current leaves, when the diode is forward biased; the names of the electrodes do not change in cases. In a vacuum tube only one electrode can emit electrons into the evacuated tube due to being heated by a filament, so electrons can only enter the device from the external circuit through the heated electrode.
Therefore this electrode is permanently named the cathode, the electrode through which the electrons exit the tube is named the anode. The polarity of voltage on an anode with respect to an associated cathode varies depending on the device type and on its operating mode. In the following examples, the anode is negative in a device that provides power, positive in a device that consumes power: In a discharging battery or galvanic cell, the anode is the negative terminal because it is where conventional current flows into "the device"; this inward current is carried externally by electrons moving outwards, negative charge flowing in one direction being electrically equivalent to positive charge flowing in the opposite direction. In a recharging battery, or an electrolytic cell, the anode is the positive terminal, which receives current from an external generator; the current through a recharging battery is opposite to the direction of current during discharge. In a diode, the anode is the positive terminal at the tail of the arrow symbol, where current flows into the device.
Note electrode naming for diodes is always based on the direction of the forward current for types such as Zener diodes or solar cells where the current of interest is the reverse current. In a cathode ray tube, the anode is the positive terminal where electrons flow out of the device, i.e. where positive electric current flows in. The word was coined in 1834 from the Greek ἄνοδος,'ascent', by William Whewell, consulted by Michael Faraday over some new names needed to complete a paper on the discovered process of electrolysis. In that paper Faraday explained that when an electrolytic cell is oriented so that electric current traverses the "decomposing body" in a direction "from East to West, or, which will strengthen this help to the memory, that in which the sun appears to move", the anode is where the current enters the electrolyte, on the East side: "ano upwards, odos a way; the use of'East' to mean the'in' direction may appear contrived. As related in the first reference cited above, Faraday had used the more straightforward term "eisode".
His motivation for changing it to something meaning'the East electrode' was to make it immune to a possible change in the direction convention for current, whose exact nature was not known at the time. The reference he used to this effect was the Earth's magnetic field direction, which at that time was believed to be invariant, he fundamentally defined his arbitrary orientation for the cell as being that in which the internal current would run parallel to and in the same direction as a hypothetical magnetizing current loop around the local line of latitude which would induce a magnetic dipole field oriented like the Earth's. This made the internal current East to West as mentioned, but in the event of a convention change it woul
In chemistry, a coordination complex consists of a central atom or ion, metallic and is called the coordination centre, a surrounding array of bound molecules or ions, that are in turn known as ligands or complexing agents. Many metal-containing compounds those of transition metals, are coordination complexes. A coordination complex whose centre is a metal atom is called a metal complex. Coordination complexes are so pervasive that their structures and reactions are described in many ways, sometimes confusingly; the atom within a ligand, bonded to the central metal atom or ion is called the donor atom. In a typical complex, a metal ion is bonded to several donor atoms, which can be the same or different. A polydentate ligand is a molecule or ion that bonds to the central atom through several of the ligand's atoms; these complexes are called chelate complexes. The central atom or ion, together with all ligands, comprise the coordination sphere; the central atoms or ion and the donor atoms comprise the first coordination sphere.
Coordination refers to the "coordinate covalent bonds" between the central atom. A complex implied a reversible association of molecules, atoms, or ions through such weak chemical bonds; as applied to coordination chemistry, this meaning has evolved. Some metal complexes are formed irreversibly and many are bound together by bonds that are quite strong; the number of donor atoms attached to the central atom or ion is called the coordination number. The most common coordination numbers are 2, 4, 6. A hydrated ion is one kind of a complex ion, a species formed between a central metal ion and one or more surrounding ligands, molecules or ions that contain at least one lone pair of electrons. If all the ligands are monodentate the number of donor atoms equals the number of ligands. For example, the cobalt hexahydrate ion or the hexaaquacobalt ion 2+ is a hydrated-complex ion that consists of six water molecules attached to a metal ion Co; the oxidation state and the coordination number reflect the number of bonds formed between the metal ion and the ligands in the complex ion.
However, the coordination number of Pt2+2 is 4 since it has two bidentate ligands, which contain four donor atoms in total. Any donor atom will give a pair of electrons. There are some donor groups which can offer more than one pair of electrons; such are called polydentate. In some cases an atom or a group offers a pair of electrons to two similar or different central metal atoms or acceptors—by division of the electron pair—into a three-center two-electron bond; these are called bridging ligands. Coordination complexes have been known since the beginning of modern chemistry. Early well-known coordination complexes include dyes such as Prussian blue, their properties were first well understood in the late 1800s, following the 1869 work of Christian Wilhelm Blomstrand. Blomstrand developed; the theory claimed that the reason coordination complexes form is because in solution, ions would be bound via ammonia chains. He compared this effect to the way. Following this theory, Danish scientist Sophus Mads Jørgensen made improvements to it.
In his version of the theory, Jørgensen claimed that when a molecule dissociates in a solution there were two possible outcomes: the ions would bind via the ammonia chains Blomstrand had described or the ions would bind directly to the metal. It was not until 1893 that the most accepted version of the theory today was published by Alfred Werner. Werner’s work included two important changes to the Blomstrand theory; the first was that Werner described the two different ion possibilities in terms of location in the coordination sphere. He claimed that if the ions were to form a chain this would occur outside of the coordination sphere while the ions that bound directly to the metal would do so within the coordination sphere. In one of Werner’s most important discoveries however he disproved the majority of the chain theory. Werner was able to discover the spatial arrangements of the ligands that were involved in the formation of the complex hexacoordinate cobalt, his theory allows one to understand the difference between a coordinated ligand and a charge balancing ion in a compound, for example the chloride ion in the cobaltammine chlorides and to explain many of the inexplicable isomers.
In 1914, Werner first resolved the coordination complex, called hexol, into optical isomers, overthrowing the theory that only carbon compounds could possess chirality. The ions or molecules surrounding the central atom are called ligands. Ligands are bound to the central atom by a coordinate covalent bond, are said to be coordinated to the atom. There are organic ligands such as alkenes whose pi bonds can coordinate to empty metal orbitals. An example is ethene in the complex known as Zeise's salt, K+−. In coordination chemistry, a structure is first described by its coordination number, the number of ligands attached to the metal. One can count the ligands attached, but sometimes the counting can become ambiguous. Coordination numbers are between two and nine, but large numbers of ligands are not uncommon for the lanthanides and actinides; the number of bonds