Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Chromium shopping experience:

1. Compare - without doubt the biggest advantage that the Chromium offers shoppers today is the ability to compare thousands of Chromium at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.

2. Research - if it has been said it will be on the internet. Ignorance is no longer a justifiable reason for buying the wrong thing. Take the time to research in detail everything that you could possible want to know about

3. Testimonials - don't know anybody that has bought a Chromium? Wrong! If the Chromium is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.

4. Questions - Got a question about Chromium then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....

5. Reputation - Never heard of the company selling Chromium? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Chromium and build up a picture of their reputation for sales, returns, customer service, delivery etc.

6. Returns - still worried that even after all of the above your Chromium wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.

7. Feedback - happy with your Chromium then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.

8. Security - check for the yellow padlock on the Chromium site before you buy, and the s after http:/ /i.e. https:// = a secure site

9. Contact - got a question about Chromium, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.

10. Payment - ready to pay for your Chromium, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.

Chromium (International Phonetic Alphabet: ) is a chemical element in the periodic table that has the symbol Cr and atomic number 24. It is a steel-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odourless, tasteless, and malleable.

History On 26 July 1761, Johann Gottlob Lehmann found an orange-red mineral in the Ural Mountains which he named Siberian red lead. Though misidentified as a lead compound with selenium and iron components, the material was in fact lead chromate with a formula of PbCrO4, now known as the mineral crocoite.

In 1770, Peter Simon Pallas visited the same site as Lehmann and found a red "lead" mineral that had very useful properties as a pigment in paints. The use of Siberian red lead as a paint pigment developed rapidly. A bright yellow made from crocoite became a color in fashion.

In 1797, Louis Nicolas Vauquelin received samples of crocoite ore. He was able to produce chromium oxide with a chemical formula of CrO3, by mixing crocoite with hydrochloric acid. In 1798, Vauquelin discovered that he could isolate metallic chromium by heating the oxide in a charcoal oven. He was also able to detect traces of chromium in precious gemstones, such as ruby, or emerald. Later that year he successfully isolated chromium atoms.

During the 1800s chromium was primarily used as a component of paints and in tanning salts but now metal alloys account for 85% of the use of chromium. The remainder is used in the chemical industry and refractory and foundry industries.

Chromium was named after the Greek word "Chrôma" meaning color, because of the many colorful compounds made from it.

Occurrence and production Chromium is mined as chromite (FeCr2O4) ore. About two-fifths of the chromite ores and concentrates in the world are produced in South Africa. Kazakhstan, India, Russia and Turkey are also substantial producers. Untapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan and southern Africa.

Approximately 15 million tons of marketable chromite ore were produced in 2000, and converted into approximately 4 million tons of ferro-chrome with an approximate market value of 2.5 billion United States dollars.

Though native chromium deposits are rare, some native chromium metal has been discovered. The Udachnaya Mine in Russia produces samples of the native metal. This mine is a kimberlite pipe rich in diamonds, and the reducing environment so provided helped produce both elemental chromium and diamond. (See also :category:Chromium minerals)

Chromium is obtained commercially by heating the ore in the presence of aluminium or silicon.

Chemical properties Chromium is a member of the transition metals, in group 6. Chromium(0) has an electronic configuration of 4s13d5, due to the lower energy of the high spin configuration. Chromium exhibits a wide range of possible oxidation states. The most common oxidation states of chromium are +2, +3, and +6, with +3 being the most stable. +1, +4 and +5 are rare. Chromium compounds of oxidation state +6 are powerful oxidants.

Chromium is passivation by oxygen, forming a thin (usually a few atoms thick being transparent because of thickness) protective oxide surface layer with another element such as nickel, and/or iron. It forms a coumpound called a spinal structure which being very dense prevents diffusion of oxygen into the underlying layer. (In iron or plain carbon steels the oxygen actually migrates into the underlying material.) Chromium is usually plated on top of a nickel layer which may or may not have been copper plated first. Chromium as opposite to most other metals such as iron and nickel does not suffer from hydrogen embrittelment. It does though suffer from nitrogen embrittelment and hence no straight chromium alloy has ever been developed. Below the pourbiax diagram can be seen, it is important to understand that the diagram only displays the thermodynamic data and it does not display any details of the rates of reaction.

for chromium in pure water, perchloric acid or sodium hydroxideIgnasi Puigdomenech, Hydra/Medusa Chemical Equilibrium Database and Plotting Software (2004) KTH Royal Institute of Technology, freely downloadable software at

Compounds See also :category:Chromium compounds.Potassium dichromate is a powerful oxidizing agent and is the preferred compound for cleaning laboratory glassware of any trace organics. It is used as a saturated solution in concentrated sulfuric acid for washing the apparatus. For this purpose, however, sodium dichromate is sometimes used because of its higher solubility (5 g/100 ml vs. 20 g/100 ml respectively).Chrome green is the green oxide of chromium, Cr2O3, used in enamel painting, and glass staining. Chrome yellow is a brilliant yellow pigment, PbCrO4, used by painters.

Chromic acid has the hypothetical structure H2CrO4. Neither chromic nor dichromic acid is found in nature, but their anions are found in a variety of compounds. Chromium trioxide, CrO3, the acid anhydride of chromic acid, is sold industrially as "chromic acid".

Chromium and the quintuple bond Chromium is notable for its ability to form quintuple covalent bonds. The synthesis of a compound of chromium(I) and a hydrocarbon Radical (chemistry) was shown via X-ray diffraction to contain a quintuple bond of length 183.51(4) pm (1.835 angstroms) joining the two central chromium atoms. This was accomplished through the use of an extremely bulky monodentate ligand which through its sheer size prevents further coordination. Chromium currently remains the only element for which quintuple bonds have been observed.

Applications Uses of chromium:

Biological role Trivalent chromium (Cr(III), or Cr3+) is required in trace amounts for sugar metabolism in humans (GTF) and its deficiency may cause a disease called chromium deficiency. In contrast, hexavalent chromium is very toxic and mutagenic when inhaled as popularized by the film Erin Brockovich (film). Cr(VI) has not been established as a carcinogen when not inhaled but in solution it is well established as a cause of allergic contact dermatitis (ACD).

Recently it was shown that the popular dietary supplement chromium picolinate complex generates chromosome damage in hamster cells. In the United States the dietary guidelines for daily chromium uptake were lowered from 50-200 microgram for an adult to 35 µg (adult male) and to 25 µg (adult female).

Isotopes Naturally occurring chromium is composed of three stable isotopes; 52Cr, 53Cr, and 54Cr with 52Cr being the most abundant (83.789% natural abundance). Nineteen radioisotopes have been characterized with the most stable being 50Cr with a half-life of (more than) 1.8x1017 years, and 51Cr with a half-life of 27.7 days. All of the remaining radioactive isotopes have half-lives that are less than 24 hours and the majority of these have half-lives that are less than 1 minute. This element also has 2 meta states.

53Cr is the radiogenic decay product of 53manganese. Chromium isotope contents are typically combined with manganese isotopic contents and have found application in isotope geology. manganese-Cr isotope ratios reinforce the evidence from 26Aluminium and 107Palladium for the early history of the solar system. Variations in 53Cr/52Cr and Mn/Cr ratios from several meteorites indicate an initial 53Mn/55Mn ratio that suggests Mn-Cr isotope systematics must result from in-situ decay of 53Mn in differentiated planetary bodies. Hence 53Cr provides additional evidence for nucleosynthesis processes immediately before coalescence of the solar system.

The isotopes of chromium range in atomic weight from 43 atomic mass unit (43Cr) to 67 u (67Cr). The primary decay mode before the most abundant stable isotope, 52Cr, is electron capture and the primary mode after is beta decay.

Precautions Chromium metal and chromium(III) compounds are not usually considered health hazards; chromium is an essential trace mineral. However, hexavalent chromium (chromium VI) compounds can be toxic if orally ingested or inhaled. The lethal dose of poisonous chromium (VI) compounds is about one half teaspoon of material. Most chromium (VI) compounds are irritating to eyes, skin and mucous membranes. Chronic exposure to chromium (VI) compounds can cause permanent eye injury, unless properly treated. Chromium(VI) is an established human carcinogen. An investigation into hexavalent chromium release into drinking water formed the plot of the motion picture Erin Brockovich (film).

World Health Organization recommended maximum allowable concentration in drinking water for chromium (VI) is 0.05 milligrams per liter. Hexavalent chromium is also one of the substances whose use is restricted by the European Restriction of Hazardous Substances Directive.

As chromium compounds were used in dyes and paints and the tanning of leather, these compounds are often found in soil and groundwater at abandoned industrial site, now needing environmental cleanup and remediation per the treatment of brownfield land. Primer (paint) containing hexavalent chromium is still widely used for aerospace and automobile refinishing applications.

See also

References

External links

Chromium (International Phonetic Alphabet: ) is a chemical element in the periodic table that has the symbol Cr and atomic number 24. It is a steel-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odourless, tasteless, and malleable.

History On 26 July 1761, Johann Gottlob Lehmann found an orange-red mineral in the Ural Mountains which he named Siberian red lead. Though misidentified as a lead compound with selenium and iron components, the material was in fact lead chromate with a formula of PbCrO4, now known as the mineral crocoite.

In 1770, Peter Simon Pallas visited the same site as Lehmann and found a red "lead" mineral that had very useful properties as a pigment in paints. The use of Siberian red lead as a paint pigment developed rapidly. A bright yellow made from crocoite became a color in fashion.

In 1797, Louis Nicolas Vauquelin received samples of crocoite ore. He was able to produce chromium oxide with a chemical formula of CrO3, by mixing crocoite with hydrochloric acid. In 1798, Vauquelin discovered that he could isolate metallic chromium by heating the oxide in a charcoal oven. He was also able to detect traces of chromium in precious gemstones, such as ruby, or emerald. Later that year he successfully isolated chromium atoms.

During the 1800s chromium was primarily used as a component of paints and in tanning salts but now metal alloys account for 85% of the use of chromium. The remainder is used in the chemical industry and refractory and foundry industries.

Chromium was named after the Greek word "Chrôma" meaning color, because of the many colorful compounds made from it.

Occurrence and production Chromium is mined as chromite (FeCr2O4) ore. About two-fifths of the chromite ores and concentrates in the world are produced in South Africa. Kazakhstan, India, Russia and Turkey are also substantial producers. Untapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan and southern Africa.

Approximately 15 million tons of marketable chromite ore were produced in 2000, and converted into approximately 4 million tons of ferro-chrome with an approximate market value of 2.5 billion United States dollars.

Though native chromium deposits are rare, some native chromium metal has been discovered. The Udachnaya Mine in Russia produces samples of the native metal. This mine is a kimberlite pipe rich in diamonds, and the reducing environment so provided helped produce both elemental chromium and diamond. (See also :category:Chromium minerals)

Chromium is obtained commercially by heating the ore in the presence of aluminium or silicon.

Chemical properties Chromium is a member of the transition metals, in group 6. Chromium(0) has an electronic configuration of 4s13d5, due to the lower energy of the high spin configuration. Chromium exhibits a wide range of possible oxidation states. The most common oxidation states of chromium are +2, +3, and +6, with +3 being the most stable. +1, +4 and +5 are rare. Chromium compounds of oxidation state +6 are powerful oxidants.

Chromium is passivation by oxygen, forming a thin (usually a few atoms thick being transparent because of thickness) protective oxide surface layer with another element such as nickel, and/or iron. It forms a coumpound called a spinal structure which being very dense prevents diffusion of oxygen into the underlying layer. (In iron or plain carbon steels the oxygen actually migrates into the underlying material.) Chromium is usually plated on top of a nickel layer which may or may not have been copper plated first. Chromium as opposite to most other metals such as iron and nickel does not suffer from hydrogen embrittelment. It does though suffer from nitrogen embrittelment and hence no straight chromium alloy has ever been developed. Below the pourbiax diagram can be seen, it is important to understand that the diagram only displays the thermodynamic data and it does not display any details of the rates of reaction.

for chromium in pure water, perchloric acid or sodium hydroxideIgnasi Puigdomenech, Hydra/Medusa Chemical Equilibrium Database and Plotting Software (2004) KTH Royal Institute of Technology, freely downloadable software at

Compounds See also :category:Chromium compounds.Potassium dichromate is a powerful oxidizing agent and is the preferred compound for cleaning laboratory glassware of any trace organics. It is used as a saturated solution in concentrated sulfuric acid for washing the apparatus. For this purpose, however, sodium dichromate is sometimes used because of its higher solubility (5 g/100 ml vs. 20 g/100 ml respectively).Chrome green is the green oxide of chromium, Cr2O3, used in enamel painting, and glass staining. Chrome yellow is a brilliant yellow pigment, PbCrO4, used by painters.

Chromic acid has the hypothetical structure H2CrO4. Neither chromic nor dichromic acid is found in nature, but their anions are found in a variety of compounds. Chromium trioxide, CrO3, the acid anhydride of chromic acid, is sold industrially as "chromic acid".

Chromium and the quintuple bond Chromium is notable for its ability to form quintuple covalent bonds. The synthesis of a compound of chromium(I) and a hydrocarbon Radical (chemistry) was shown via X-ray diffraction to contain a quintuple bond of length 183.51(4) pm (1.835 angstroms) joining the two central chromium atoms. This was accomplished through the use of an extremely bulky monodentate ligand which through its sheer size prevents further coordination. Chromium currently remains the only element for which quintuple bonds have been observed.

Applications Uses of chromium:

Biological role Trivalent chromium (Cr(III), or Cr3+) is required in trace amounts for sugar metabolism in humans (GTF) and its deficiency may cause a disease called chromium deficiency. In contrast, hexavalent chromium is very toxic and mutagenic when inhaled as popularized by the film Erin Brockovich (film). Cr(VI) has not been established as a carcinogen when not inhaled but in solution it is well established as a cause of allergic contact dermatitis (ACD).

Recently it was shown that the popular dietary supplement chromium picolinate complex generates chromosome damage in hamster cells. In the United States the dietary guidelines for daily chromium uptake were lowered from 50-200 microgram for an adult to 35 µg (adult male) and to 25 µg (adult female).

Isotopes Naturally occurring chromium is composed of three stable isotopes; 52Cr, 53Cr, and 54Cr with 52Cr being the most abundant (83.789% natural abundance). Nineteen radioisotopes have been characterized with the most stable being 50Cr with a half-life of (more than) 1.8x1017 years, and 51Cr with a half-life of 27.7 days. All of the remaining radioactive isotopes have half-lives that are less than 24 hours and the majority of these have half-lives that are less than 1 minute. This element also has 2 meta states.

53Cr is the radiogenic decay product of 53manganese. Chromium isotope contents are typically combined with manganese isotopic contents and have found application in isotope geology. manganese-Cr isotope ratios reinforce the evidence from 26Aluminium and 107Palladium for the early history of the solar system. Variations in 53Cr/52Cr and Mn/Cr ratios from several meteorites indicate an initial 53Mn/55Mn ratio that suggests Mn-Cr isotope systematics must result from in-situ decay of 53Mn in differentiated planetary bodies. Hence 53Cr provides additional evidence for nucleosynthesis processes immediately before coalescence of the solar system.

The isotopes of chromium range in atomic weight from 43 atomic mass unit (43Cr) to 67 u (67Cr). The primary decay mode before the most abundant stable isotope, 52Cr, is electron capture and the primary mode after is beta decay.

Precautions Chromium metal and chromium(III) compounds are not usually considered health hazards; chromium is an essential trace mineral. However, hexavalent chromium (chromium VI) compounds can be toxic if orally ingested or inhaled. The lethal dose of poisonous chromium (VI) compounds is about one half teaspoon of material. Most chromium (VI) compounds are irritating to eyes, skin and mucous membranes. Chronic exposure to chromium (VI) compounds can cause permanent eye injury, unless properly treated. Chromium(VI) is an established human carcinogen. An investigation into hexavalent chromium release into drinking water formed the plot of the motion picture Erin Brockovich (film).

World Health Organization recommended maximum allowable concentration in drinking water for chromium (VI) is 0.05 milligrams per liter. Hexavalent chromium is also one of the substances whose use is restricted by the European Restriction of Hazardous Substances Directive.

As chromium compounds were used in dyes and paints and the tanning of leather, these compounds are often found in soil and groundwater at abandoned industrial site, now needing environmental cleanup and remediation per the treatment of brownfield land. Primer (paint) containing hexavalent chromium is still widely used for aerospace and automobile refinishing applications.

See also

References

External links



chromium
Describes and explains some features of chromium chemistry ... This page looks at some aspects of chromium chemistry required for UK A level (and its equivalents).

Chromium - Wikipedia, the free encyclopedia
Chromium (pronounced /ˈkroʊmiəm/) is a chemical element which has the symbol Cr and atomic number 24. It is a steel-gray, lustrous, hard metal that takes a high polish and has a ...

Food Standards Agency - Eat well, be well - Chromium
Chromium is a trace element found widely in the environment. It's found in the air, water and soil, and in plants and animals.

Chromium Homepage
Chromium Homepage. Chromium is a system for interactive rendering on clusters of graphics workstations. Various parallel rendering techniques such as sort-first and sort-last may ...

Chromium and you
CHROMIUM AND YOU. ARE YOU AT RISK? Working with chromium and its inorganic compounds can affect your health. This leaflet tells you about possible health hazards from working with ...

Visual Elements - Chromium
Discovered : 1780 by N.L. Vauquelin Isolated in Paris, France Origin : The name is derived from the Greek ‘chroma’ meaning colour. Description

Chromium
Chromium analysis offered by The Trace Element and Micronutrient Unit at Glasgow Royal Infirmary, Glasgow, UK

SourceForge.net: The Chromium Project
The world's largest development and download repository of Open Source code and applications ... Chromium is a flexible framework for scalable real-time rendering on clusters of ...

Dietary Supplement Fact Sheet: Chromium
Table of Contents. Chromium: What is it? What foods provide chromium? What are recommended intakes of chromium? What affects chromium levels in the body?

Cancer Research UK : Cigarette smoke contains 69 chemicals ...
Find out about the cancer-causing chemicals in cigarette smoke including arsenic, benzene, formaldehyde, cadmium, polonium, chromium and more.

 

Chromium



 
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