What foods contain chromium, and how is it beneficial for the body? What is Chrome Web Lab

Chrome - chemical element with atomic number 24. It is a hard, shiny, steel-gray metal that polishes well and does not tarnish. Used in alloys such as stainless steel and as a coating. The human body requires small amounts of trivalent chromium to metabolize sugar, but Cr(VI) is highly toxic.

Various chromium compounds, such as chromium(III) oxide and lead chromate, are brightly colored and used in paints and pigments. The red color of ruby ​​is due to the presence of this chemical element. Some substances, especially sodium, are oxidizing agents used to oxidize organic compounds and (together with sulfuric acid) to clean laboratory glassware. In addition, chromium (VI) oxide is used in the production of magnetic tape.

Discovery and etymology

The history of the discovery of the chemical element chromium is as follows. In 1761, Johann Gottlob Lehmann found an orange-red mineral in the Ural Mountains and named it “Siberian red lead.” Although it was erroneously identified as a compound of lead with selenium and iron, the material was actually lead chromate with the chemical formula PbCrO 4 . Today it is known as the mineral croconte.

In 1770, Peter Simon Pallas visited the site where Lehmann found a red lead mineral that had a very beneficial features pigment in paints. The use of Siberian red lead as paint has received fast development. In addition, the bright yellow color of crocont has become fashionable.

In 1797, Nicolas-Louis Vauquelin obtained samples of red. By mixing croconte with hydrochloric acid, he obtained CrO 3 oxide. Chromium was isolated as a chemical element in 1798. Vauquelin obtained it by heating the oxide with charcoal. He was also able to detect traces of chromium in precious stones, such as ruby ​​and emerald.

In the 1800s, Cr was primarily used in dyes and tanning salts. Today, 85% of the metal is used in alloys. The remainder is used in the chemical, refractory and foundry industries.

The pronunciation of the chemical element chromium corresponds to the Greek χρῶμα, meaning "color", due to the variety of colored compounds that can be obtained from it.

Mining and production

The element is produced from chromite (FeCr 2 O 4). About half of the world's ore is mined in South Africa. In addition, Kazakhstan, India and Türkiye are his major manufacturers. There are enough explored deposits of chromite, but geographically they are concentrated in Kazakhstan and southern Africa.

Deposits of native chromium metal are rare, but they do exist. For example, it is mined at the Udachnaya mine in Russia. It is rich in diamonds, and the reducing environment helped produce pure chromium and diamonds.

For industrial metal production, chromite ores are treated with molten alkali (caustic soda, NaOH). In this case, sodium chromate (Na 2 CrO 4) is formed, which is reduced by carbon to the oxide Cr 2 O 3. The metal is produced by heating the oxide in the presence of aluminum or silicon.

In 2000, approximately 15 million tons of chromite ore were mined and processed into 4 million tons of ferrochrome, a 70% chromium-iron alloy, with an approximate market value of US$2.5 billion.

Main characteristics

The characteristics of the chemical element chromium are due to the fact that it is a transition metal fourth period periodic table and is located between vanadium and manganese. Included in group VI. Melts at a temperature of 1907 °C. In the presence of oxygen, chromium quickly forms a thin layer of oxide, which protects the metal from further interaction with oxygen.

As a transition element, it reacts with substances in different proportions. Thus it forms compounds in which it has various degrees oxidation. Chromium is a chemical element with the basic states +2, +3 and +6, of which +3 is the most stable. In addition, in rare cases conditions +1, +4 and +5 are observed. Chromium compounds in the +6 oxidation state are strong oxidizing agents.

What color is chrome? The chemical element gives the ruby ​​hue. The Cr 2 O 3 used for is also used as a pigment called chrome green. Its salts color glass emerald green. Chromium is the chemical element whose presence makes rubies red. Therefore, it is used in the production of synthetic rubies.

Isotopes

Isotopes of chromium have atomic weights from 43 to 67. Typically, this chemical element consists of three stable forms: 52 Cr, 53 Cr and 54 Cr. Of these, 52 Cr is the most common (83.8% of all natural chromium). In addition, 19 radioisotopes have been described, of which the most stable is 50 Cr with a half-life exceeding 1.8x10 17 years. 51 Cr has a half-life of 27.7 days, and for all other radioactive isotopes it does not exceed 24 hours, and for most of them it lasts less than one minute. The element also has two meta states.

Isotopes of chromium in earth's crust, as a rule, accompany manganese isotopes, which is used in geology. 53 Cr is formed during the radioactive decay of 53 Mn. Mn/Cr isotope ratios support other early history clues solar system. Changes in the 53 Cr/ 52 Cr and Mn/Cr ratios from different meteorites prove that new atomic nuclei were created just before the formation of the Solar System.

Chemical element chromium: properties, formula of compounds

Chromium(III) oxide Cr 2 O 3, also known as sesquioxide, is one of the four oxides of this chemical element. It is obtained from chromite. The green color compound is commonly called "chrome green" when used as a pigment for enamel and glass painting. The oxide can dissolve in acids, forming salts, and in molten alkali - chromites.

Potassium dichromate

K 2 Cr 2 O 7 is a powerful oxidizing agent and is preferred as a means for cleaning laboratory glassware from organic matter. For this purpose, its saturated solution is used. Sometimes, however, it is replaced with sodium bichromate, based on the higher solubility of the latter. In addition, it can regulate the oxidation process of organic compounds, converting primary alcohol into aldehyde and then into carbon dioxide.

Potassium dichromate can cause chrome dermatitis. Chromium is likely to cause sensitization leading to the development of dermatitis, especially of the hands and forearms, which is chronic and difficult to cure. Like other Cr(VI) compounds, potassium dichromate is carcinogenic. It must be handled with gloves and appropriate protective equipment.

Chromic acid

The compound has the hypothetical structure H 2 CrO 4 . Neither chromic nor dichromic acids occur in nature, but their anions are found in various substances. The “chromic acid” that can be found on sale is actually its acid anhydride - CrO 3 trioxide.

Lead(II) chromate

PbCrO 4 has a bright yellow color and is practically insoluble in water. For this reason, it has found use as a coloring pigment called crown yellow.

Cr and pentavalent bond

Chromium is distinguished by its ability to form pentavalent bonds. The compound is created by Cr(I) and a hydrocarbon radical. A pentavalent bond is formed between two chromium atoms. Its formula can be written as Ar-Cr-Cr-Ar, where Ar represents a specific aromatic group.

Application

Chromium is a chemical element whose properties have given it many different uses, some of which are listed below.

It gives metals corrosion resistance and a glossy surface. Therefore, chromium is included in alloys such as stainless steel, used, for example, in cutlery. It is also used for chrome plating.

Chromium is a catalyst for various reactions. It is used to make molds for firing bricks. Its salts are used to tan leather. Potassium bichromate is used for the oxidation of organic compounds such as alcohols and aldehydes, as well as for cleaning laboratory glassware. It serves as a fixing agent for fabric dyeing and is also used in photography and photo printing.

CrO 3 is used for the manufacture of magnetic tapes (for example, for audio recordings), which have best characteristics than films with iron oxide.

Role in biology

Trivalent chromium is a chemical element necessary for the metabolism of sugar in the human body. In contrast, hexavalent Cr is highly toxic.

Precautionary measures

Chromium metal and Cr(III) compounds are generally not considered a health hazard, but substances containing Cr(VI) can be toxic if ingested or inhaled. Most of these substances are irritating to the eyes, skin and mucous membranes. With chronic exposure, chromium(VI) compounds can cause eye damage if not treated properly. In addition, it is a recognized carcinogen. Lethal dose of this chemical element - about half a teaspoon. According to recommendations World Organization health care, extremely permissible concentration Cr(VI) in drinking water is 0.05 mg per liter.

Because chromium compounds are used in dyes and to tan leather, they are often found in soil and groundwater from abandoned industrial sites requiring environmental cleanup and remediation. Primer containing Cr(VI) is still widely used in the aerospace and automotive industries.

Element properties

Basic physical properties chromium are as follows:

• Atomic number: 24.
• Atomic weight: 51.996.
• Melting point: 1890 °C.
• Boiling point: 2482 °C.
• Oxidation state: +2, +3, +6.
• Electron configuration: 3d 5 4s 1.

Google Chrome is a product of one of the most powerful search engines, Google. The founding date of the corporation is considered to be 1998. Google's Chrome browser launched in 2008. Gaining its audience at a good pace, it is becoming one of the most popular browsers for computer and mobile devices. Now the number of its users numbers hundreds of millions of people. The browser is used on almost every second computer in the world. Let's take a closer look at what Chrome is, how to install it correctly and what capabilities it has.

Google Corporation. Start

Everyone knows that Google is, first of all, search system. Today, Google is a huge transnational corporation with offices in many countries, and the main one in the United States.

And it all started back in 1996. Two California students, Sergey Brin and Larry Page, were engaged in a research project designed to develop new technologies for a digital universal library. During the research, students studied the mathematical properties of the then existing World Wide Web. This is how their search robot was created, which found the necessary sites, offered a list of them, assessing, first of all, the importance of the information, and not the most large quantity a certain word encountered on the site, as the search engines that existed at that time did.

After that, investors were found for such a brainchild of students. The new search system, having undergone many improvements, began to very quickly win the hearts of users.

The birth of a new browser

What is "Chrome"? At first, the management of Google Corporation did not even think about creating a new browser, because the niche was already sufficiently filled. And frankly speaking, the creators of the powerful corporation were afraid of the resounding failure of the browser project. But, having powerful financial resources, they decided to try to sketch out a project and submit it to management. Oddly enough, it was approved - due to its simplicity, clarity and pleasant use.

In the fall of 2008, the first version of the Google Chrome browser was released for operating system Windows. Thanks to the huge budget invested in the new brainchild, the browser quickly overcomes the path from unknown to very popular.

Google Chrome browser. What it is

The Chrome browser from Google is developed based on the free Chromium browser, which is the “father” of many existing browsers. The developers of the program decided to use the Webkit engine as the basis for its work, but in 2013 the Google Chrome browser switched to the Blink engine.

Now the Google Chrome browser positions itself as a simple, fast and secure software product. Of course, it proves this with its popularity, convenient, uncluttered interface, high level of security, which can be discussed separately, and many applications and extensions for every taste. It can also be noted that a browser like Chrome does not stand still, constantly improving its numerous services.

Advantages of the Chrome browser

Following the saying “Everything ingenious is simple,” Google Chrome has many advantages that have given it such popularity. Among them we can note fast page browsing and a minimalistic design in which nothing distracts from the web page.

If you would not like to view your browsing history after use, the “incognito” mode will ensure your privacy. Due to the fact that the search bar is combined with the address bar, there is no need to enter the full site address. To synchronize user data, Google links this data with each other, storing it on a cloud server. If necessary, you can log into your account from any computer and access your bookmarks and necessary information. This handy feature comes in handy if the browser is removed.

Program failure control will not allow you to interrupt work at the wrong time. Also pleasing is the browser’s versatility for all operating systems. Many people probably know that Chrome is a browser that can be installed on any operating system and electronic device. To ensure the safety of its users, Google Chrome maintains a blacklist of malicious sites, and also notifies about a possible threat when going to one or another unknown page. This browser has many advantages, but the main thing about Chrome is its high speed.

Installation

Download the Google Chrome browser for free. The best way to do this is from the official page. Before downloading, make sure your device is compatible system requirements. So, Windows for Chrome should start with version seven. The Intel Pentium processor must be fourth generation or later. To install Chrome on an Android mobile device, you must use a version of the operating system that cannot be earlier than Android 4.1. iOS system must start with 9 or later versions.

After the Chrome installation file has been downloaded for free, you must click the “Run” or “Save” button. Then, double-click the mouse to launch the saved installed file and use the Google Chrome browser.

Importing settings

If necessary, you can import user settings from other browsers into the installed Google Chrome browser, after which information such as the start page, browsing history, bookmarks, and account passwords will be available.

Before importing, you need to close all open browsers, launch Chrome, and in its upper right corner go to the settings menu, which is depicted as three vertical dots. Click “Bookmarks”, then “Import bookmarks and settings” and select the browser from which you want to import data. If the list provided does not contain the browser you need, you need to export the bookmarks from it to HTML format, and then select the “HTML file with bookmarks” option when importing into Chrome. When you click the "Import" button, all settings from the previous browser will be moved to Chrome.

Update

The Chrome browser updates automatically when you restart or background. But if it is always on, you can skip its update. To see if a newer version of Chrome is available, you need to pay attention to the color of the Google Chrome Settings and Controls menu indicator in the upper right corner of the screen. Green will mean that the new version was released about two days ago, orange - four days ago, red - seven days ago.

To update Chrome manually, you need to open the browser, go to the “Setting and managing Google Chrome” menu, select the “Update” option Google Chrome"(the absence of such a position means that the browser version is already new) and click "Restart". All open windows and bookmarks in the browser will be saved and loaded automatically when you launch it again. The restart can be delayed by clicking the "Not Now" button.

Removal

If you need to remove the Chrome browser, you need to exit it and go to the control panel of your operating system (in the lower left corner). Then open “Options (Settings)”, select the “Applications” item, find “Google Chrome” and select the “Uninstall” action (for Windows 8 and 10). For Windows 7 or Vista, in Settings, select Control Panel, then go to Uninstall a program or Programs and Features. Double-click on Google Chrome. The browser will be removed by clicking the "Delete" button.

To clear your profile data, you must click “Also delete browsing data.” But if you synchronize your data and sign back into your Google account, some of your information will be available because it is stored on the Google server. To clear everything completely, you need to clear the history. You can do this by going to the “Customize and manage Google Chrome” menu, then select “More tools”, and then “Delete browsing data”. After specifying the required time range, check the boxes for the type of information you want to delete, then click “Clear history.”

Applications and extensions

The Chrome browser from Google offers a lot of different extensions, plugins and applications for users, both paid and free. In fact, thanks to extensions for every taste, you can design the Chrome browser to suit you. Find required application or the extension can be found in the official online store.

If extensions are the addition and improvement of browser functions, then applications are separate programs that run directly in the browser.

How to add or remove an application or extension

To add extensions or add-ons to the Chrome browser, you need to select “Extensions” or “Applications” in the Chrome online store in the left column. Then select what you need from the catalog that opens, and you can use the search. An “Install” button will appear next to the position of the desired application or extension. If you add an extension, you need to check what data it will have access to, then click “Install extension”. After this, the installed Chrome applications will appear on the launcher, and the extensions that appear can be seen as buttons on the Chrome toolbar.

To remove an unnecessary extension, you need to go to the “Customize and manage Google Chrome” menu, then select the “Additional tools” item and from there - “Extensions”. In the list that opens, select the extension to be removed and click on the “Remove from Chrome” button, then click “Delete” again. The application can be removed from the "Toolbar" on the desktop.

Useful extensions and applications

Those who keep up with the times have long been using convenient and useful extensions and applications in their browser. Their functionality can be varied - from work assistants to games and entertainment. Let's look at some interesting extensions and applications from Google Chrome:

DataSaver is your faithful assistant in saving traffic. It has the function of compressing downloaded pages, text and images. Very convenient for mobile devices. It is already built-in in versions for Android or iOS (“Settings” - “Traffic saving”).

Quick Notes is a notepad that pops up online as a window at your request. Helps you instantly write down a thought that came to you on any page on the Internet.

XTranslate - this extension will provide instant translation of both individual words and entire web pages, you just need to select the required text.

Gmail Offline - allows you to work with mail in the absence of the Internet. True, it is still necessary to receive and send letters. But you can type the answer slowly.

Save to Pocket - will save the web page for later reading, while clearing advertising and unnecessary elements, leaving only text and images. The page will be saved in the cache and will be accessible even without the Internet.

Finally

So what is Chrome? This is a modern and useful browser. The review of popular applications and extensions for it can be continued ad infinitum. However, it's up to you to decide which app or extension you need. A large selection, their diversity and accessibility for the Google Chrome browser makes our lives easier and brighter, helps in work, study, or allows us to pass the time with gaming applications.

"National Research Tomsk Polytechnic University"

Institute of Natural Resources Geoecology and Geochemistry

Chromium

By discipline:

Chemistry

Completed:

student of group 2G41 Tkacheva Anastasia Vladimirovna 10.29.2014

Checked:

teacher Stas Nikolay Fedorovich

Position in the periodic table

Chromium- element of the side subgroup of the 6th group of the 4th period of the periodic system of chemical elements of D. I. Mendeleev with atomic number 24. Denoted by the symbol Cr(lat. Chromium). Simple substance chromium- hard metal of bluish-white color. Chrome is sometimes classified as a ferrous metal.

Atomic structure

17 Cl)2)8)7 - atomic structure diagram

1s2s2p3s3p - electronic formula

The atom is located in the III period, and has three energy levels

The atom is located in group VII, in the main subgroup - at the outer energy level 7 electrons

Element properties

Physical properties

Chrome is a white shiny metal with a cubic body-centered lattice, a = 0.28845 nm, characterized by hardness and brittleness, with a density of 7.2 g/cm 3, one of the hardest pure metals (second only to beryllium, tungsten and uranium), with a melting point of 1903 degrees. And with a boiling point of about 2570 degrees. C. In air, the surface of chromium is covered with an oxide film, which protects it from further oxidation. Adding carbon to chromium further increases its hardness.

Chemical properties

Chromium is an inert metal under normal conditions, but when heated it becomes quite active.

Interaction with non-metals

When heated above 600°C, chromium burns in oxygen:

4Cr + 3O 2 = 2Cr 2 O 3.

Reacts with fluorine at 350°C, with chlorine at 300°C, with bromine at red heat, forming chromium (III) halides:

2Cr + 3Cl2 = 2CrCl3.

Reacts with nitrogen at temperatures above 1000°C to form nitrides:

2Cr + N 2 = 2CrN

or 4Cr + N 2 = 2Cr 2 N.

2Cr + 3S = Cr 2 S 3.

Reacts with boron, carbon and silicon to form borides, carbides and silicides:

Cr + 2B = CrB 2 (possible formation of Cr 2 B, CrB, Cr 3 B 4, CrB 4),

2Cr + 3C = Cr 2 C 3 (possible formation of Cr 23 C 6, Cr 7 B 3),

Cr + 2Si = CrSi 2 (possible formation of Cr 3 Si, Cr 5 Si 3, CrSi).

Does not interact directly with hydrogen.

Interaction with water

When finely ground and hot, chromium reacts with water to form chromium(III) oxide and hydrogen:

2Cr + 3H 2 O = Cr 2 O 3 + 3H 2

Interaction with acids

In the electrochemical voltage series of metals, chromium is located before hydrogen; it displaces hydrogen from solutions of non-oxidizing acids:

Cr + 2HCl = CrCl 2 + H 2;

Cr + H 2 SO 4 = CrSO 4 + H 2.

In the presence of atmospheric oxygen, chromium (III) salts are formed:

4Cr + 12HCl + 3O 2 = 4CrCl 3 + 6H 2 O.

Concentrated nitrogen and sulfuric acid passivate chrome. Chromium can dissolve in them only with strong heating; chromium (III) salts and acid reduction products are formed:

2Cr + 6H 2 SO 4 = Cr 2 (SO 4) 3 + 3SO 2 + 6H 2 O;

Cr + 6HNO 3 = Cr(NO 3) 3 + 3NO 2 + 3H 2 O.

Interaction with alkaline reagents

Chromium does not dissolve in aqueous solutions of alkalis; it slowly reacts with alkali melts to form chromites and release hydrogen:

2Cr + 6KOH = 2KCrO 2 + 2K 2 O + 3H 2.

Reacts with alkaline melts of oxidizing agents, for example potassium chlorate, and chromium is converted into potassium chromate:

Cr + KClO 3 + 2KOH = K 2 CrO 4 + KCl + H 2 O.

Recovery of metals from oxides and salts

Chromium is an active metal, capable of displacing metals from solutions of their salts: 2Cr + 3CuCl 2 = 2CrCl 3 + 3Cu.

Properties of a simple substance

Stable in air due to passivation. For the same reason, it does not react with sulfuric and nitric acids. At 2000 °C it burns to form green chromium(III) oxide Cr 2 O 3, which has amphoteric properties.

Compounds of chromium with boron (borides Cr 2 B, CrB, Cr 3 B 4, CrB 2, CrB 4 and Cr 5 B 3), with carbon (carbides Cr 23 C 6, Cr 7 C 3 and Cr 3 C 2), were synthesized. with silicon (silicides Cr 3 Si, Cr 5 Si 3 and CrSi) and nitrogen (nitrides CrN and Cr 2 N).

Cr(+2) compounds

The oxidation state +2 corresponds to the basic oxide CrO (black). Cr 2+ salts (blue solutions) are obtained by reducing Cr 3+ salts or dichromates with zinc in an acidic medium (“hydrogen at the time of release”):

All these Cr 2+ salts are strong reducing agents, to the point that when standing, they displace hydrogen from water. Oxygen in the air, especially in an acidic environment, oxidizes Cr 2+, as a result of which the blue solution quickly turns green.

Brown or yellow hydroxide Cr(OH) 2 precipitates when alkalis are added to solutions of chromium(II) salts.

Chromium dihalides CrF 2, CrCl 2, CrBr 2 and CrI 2 were synthesized

Cr(+3) compounds

The oxidation state +3 corresponds to the amphoteric oxide Cr 2 O 3 and hydroxide Cr (OH) 3 (both green). This is the most stable oxidation state of chromium. Chromium compounds in this oxidation state range in color from dirty purple (3+ ion) to green (anions are present in the coordination sphere).

Cr 3+ is prone to the formation of double sulfates of the form M I Cr(SO 4) 2 12H 2 O (alum)

Chromium (III) hydroxide is obtained by reacting ammonia with solutions of chromium (III) salts:

Cr+3NH+3H2O→Cr(OH)↓+3NH

You can use alkali solutions, but in their excess a soluble hydroxo complex is formed:

Cr+3OH→Cr(OH)↓

Cr(OH)+3OH→

By fusing Cr 2 O 3 with alkalis, chromites are obtained:

Cr2O3+2NaOH→2NaCrO2+H2O

Uncalcined chromium(III) oxide dissolves in alkaline solutions and acids:

Cr2O3+6HCl→2CrCl3+3H2O

When chromium(III) compounds are oxidized in an alkaline environment, chromium(VI) compounds are formed:

2Na+3HO→2NaCrO+2NaOH+8HO

The same thing happens when chromium (III) oxide is fused with alkali and oxidizing agents, or with alkali in air (the melt acquires a yellow color):

2Cr2O3+8NaOH+3O2→4Na2CrO4+4H2O

Chromium compounds (+4)[

By careful decomposition of chromium(VI) oxide CrO 3 under hydrothermal conditions, chromium(IV) oxide CrO 2 is obtained, which is ferromagnetic and has metallic conductivity.

Among chromium tetrahalides, CrF 4 is stable, chromium tetrachloride CrCl 4 exists only in vapors.

Chromium compounds (+6)

The oxidation state +6 corresponds to the acidic chromium (VI) oxide CrO 3 and a number of acids, between which there is an equilibrium. The simplest of them are chromium H 2 CrO 4 and dichromium H 2 Cr 2 O 7 . They form two series of salts: yellow chromates and orange dichromates, respectively.

Chromium (VI) oxide CrO 3 is formed by the interaction of concentrated sulfuric acid with solutions of dichromates. A typical acidic oxide, when interacting with water it forms strong unstable chromic acids: chromic H 2 CrO 4, dichromic H 2 Cr 2 O 7 and other isopoly acids with the general formula H 2 Cr n O 3n+1. An increase in the degree of polymerization occurs with a decrease in pH, that is, an increase in acidity.

Chromium

CHROMIUM-A; m.[from Greek chrōma - color, paint]

1. Chemical element (Cr), a hard metal of a steel-gray color (used in the manufacture of hard alloys and for coating metal products).

2. Soft thin leather tanned with salts of this metal. Boots made of chrome.

3. A type of yellow paint obtained from chromates.

◁ Chrome (see).

(lat. Chromium), chemical element of group VI of the periodic table. Named from the Greek. chrōma - color, paint (due to the bright color of the compounds). Bluish-silver metal; density 7.19 g/cm 3, t pl 1890°C. Does not oxidize in air. The main minerals are chrome spinels. Chromium is an essential component of stainless, acid-resistant, heat-resistant steels and large number other alloys (nichrome, lame, stellite). Used for chrome plating. Chromium compounds are oxidizing agents, inorganic pigments, tanning agents.

CHROME (Latin chromium, from the Greek chromium - color, color, chromium compounds are characterized by a wide color palette), Cr (read “chrome”), a chemical element with atomic number 24, atomic mass 51.9961. Located in group VIB in the 4th period of the periodic table of elements.
Natural chromium consists of a mixture of four stable nuclides: 50 Cr (mixture content 4.35%), 52 Cr (83.79%), 53 Cr (9.50%) and 54 Cr (2.36%). Configuration of two outer electronic layers 3s 2 R 6 d 5 4s 1 . Oxidation states range from 0 to +6, the most typical are +3 (the most stable) and +6 (valences III and VI).
Neutral atom radius 0.127 nm, ion radius (coordination number 6): Cr 2+ 0.073 nm, Cr 3+ 0.0615 nm, Cr 4+ 0.055 nm, Cr 5+ 0.049 nm and Cr 6+ 0.044 nm. The sequential ionization energies are 6.766, 16.49, 30.96, 49.1, 69.3 and 90.6 eV. Electron affinity 1.6 eV. Electronegativity according to Pauling (cm. PAULING Linus) 1,66.
History of discovery
In 1766, a mineral was discovered in the vicinity of Yekaterinburg, which was called “Siberian red lead,” PbCrO 4. Modern name- crocoite. In 1797, the French chemist L. N. Vauquelin (cm. VAUCLIN Louis Nicolas) isolated a new refractory metal from it (most likely Vauquelin obtained chromium carbide).
Being in nature
Content in the earth's crust is 0.035% by weight. IN sea ​​water chromium content 2·10 -5 mg/l. Chromium is practically never found in free form. It is part of more than 40 different minerals (chromite FeCr 2 O 4, volkonskoite, uvarovite, vokelenite, etc.). Some meteorites contain chromium sulfide compounds.
Receipt
The industrial raw material for the production of chromium and chromium-based alloys is chromite. By reducing chromite melting with coke (reducing agent), iron ore and other components, ferrochrome with a chromium content of up to 80% (by weight) is obtained.
To obtain pure metal chromium, chromite is fired with soda and limestone in furnaces:
2Cr 2 O 3 + 2Na 2 CO 3 + 3O 2 = 4Na 2 CrO 4 + 4CO 2
The resulting sodium chromate Na 2 CrO 4 is leached with water, the solution is filtered, evaporated and treated with acid. In this case, Na 2 CrO 4 chromate transforms into Na 2 Cr 2 O 7 dichromate:
2Na 2 CrO 4 + H 2 SO 4 = Na 2 Cr 2 O 7 + Na 2 SO 4 + H 2 O
The resulting dichromate is reduced with sulfur:
Na 2 Cr 2 O 7 + 3S = Na 2 S + Cr 2 O 3 + 2SO 2,
The resulting pure chromium(III) oxide Cr 2 O 3 is subjected to aluminothermy:
Cr 2 O 3 + 2Al = Al 2 O 3 + 2Cr.
Silicon is also used:
2Cr 2 O 3 + 3Si = 3SiO 2 + 4Cr
To obtain high-purity chromium, technical chromium is electrochemically purified from impurities.
Physical and Chemical properties
In its free form, it is a bluish-white metal with a cubic body-centered lattice, A= 0.28845 nm. At a temperature of 39°C it changes from a paramagnetic state to an antiferromagnetic state (Néel point). Melting point 1890°C, boiling point 2680°C. Density 7.19 kg/dm3.
Stable in air. At 300°C it burns to form green chromium (III) oxide Cr 2 O 3, which has amphoteric properties. By fusing Cr 2 O 3 with alkalis, chromites are obtained:
Cr 2 O 3 + 2NaOH = 2NaCrO 2 + H 2 O
Uncalcined chromium(III) oxide easily dissolves in alkaline solutions and acids:
Cr 2 O 3 + 6HCl = 2CrCl 3 + 3H 2 O
The thermal decomposition of chromium carbonyl Cr(OH) 6 produces red basic chromium(II) oxide CrO. Brown or yellow hydroxide Cr(OH) 2 with weakly basic properties is precipitated when alkalis are added to solutions of chromium(II) salts.
Careful decomposition of chromium(VI) oxide CrO 3 under hydrothermal conditions produces chromium(IV) dioxide CrO 2, which is ferromagnetic and has metallic conductivity.
When concentrated sulfuric acid reacts with solutions of dichromates, red or violet-red crystals of chromium(VI) oxide CrO 3 are formed. A typically acidic oxide, when interacting with water it forms strong unstable chromic acids: chromic H 2 CrO 4 , dichromic H 2 Cr 2 O 7 and others.
Halides are known that correspond to different oxidation states of chromium. Chromium dihalides CrF 2, CrCl 2, CrBr 2 and CrI 2 and trihalides CrF 3, CrCl 3, CrBr 3 and CrI 3 were synthesized. However, unlike similar compounds of aluminum and iron, CrCl 3 trichloride and chromium tribromide CrBr 3 are non-volatile.
Among chromium tetrahalides, CrF 4 is stable, chromium tetrachloride CrCl 4 exists only in vapors. Chromium hexafluoride CrF 6 is known.
Chromium oxyhalides CrO 2 F 2 and CrO 2 Cl 2 were obtained and characterized.
Compounds of chromium with boron (borides Cr 2 B, CrB, Cr 3 B 4, CrB 2, CrB 4 and Cr 5 B 3), with carbon (carbides Cr 23 C 6, Cr 7 C 3 and Cr 3 C 2), were synthesized. with silicon (silicides Cr 3 Si, Cr 5 Si 3 and CrSi) and nitrogen (nitrides CrN and Cr 2 N).
Chromium(III) compounds are the most stable in solutions. In this oxidation state, chromium corresponds to both the cationic form and the anionic forms, for example, the 3- anion existing in an alkaline environment.
When chromium(III) compounds are oxidized in an alkaline environment, chromium(VI) compounds are formed:
2Na 3 + 3H 2 O 2 = 2Na 2 CrO 4 + 2NaOH + 8H 2 O
Cr (VI) corresponds to a number of acids that exist only in aqueous solutions: chromic H 2 CrO 4 , dichromic H 2 Cr 2 O 7 , trichromic H 3 Cr 3 O 10 and others that form salts - chromates, dichromates, trichromates, etc. .
Depending on the acidity of the environment, the anions of these acids easily convert into each other. For example, when a yellow solution of potassium chromate K 2 CrO 4 is acidified, orange potassium dichromate K 2 Cr 2 O 7 is formed:
2K 2 CrO 4 + 2HCl = K 2 Cr 2 O 7 + 2KCl + H 2 O
But if an alkali solution is added to the orange solution of K 2 Cr 2 O 7, the color turns yellow again because potassium chromate K 2 CrO 4 is formed again:
K 2 Cr 2 O 7 + 2KOH = 2K 2 CrO 4 + H 2 O
When a barium salt solution is added to a yellow solution containing chromate ions, a yellow precipitate of barium chromate BaCrO 4 precipitates:
Ba 2+ + CrO 4 2- = BaCrO 4
Chromium(III) compounds are strong oxidizing agents, for example:
K 2 Cr 2 O 7 + 14 HCl = 2CrCl 3 + 2KCl + 3Cl 2 + 7H 2 O
Application
The use of chromium is based on its heat resistance, hardness and corrosion resistance. They are used to produce alloys: stainless steel, nichrome, etc. A large amount of chromium is used for decorative corrosion-resistant coatings. Chromium compounds are fire-resistant materials. Chromium (III) oxide is a green paint pigment, also included in abrasive materials (GOI pastes). The color change upon reduction of chromium(VI) compounds is used to conduct a rapid analysis of the alcohol content in exhaled air.
The Cr 3+ cation is part of potassium chromium KCr(SO 4) 2 ·12H 2 O alum used in leather tanning.
Physiological action
Chrome is one of nutrients, is constantly included in the tissues of plants and animals. In animals, chromium is involved in the metabolism of lipids, proteins (part of the enzyme trypsin), and carbohydrates. A decrease in chromium content in food and blood leads to a decrease in growth rate and an increase in cholesterol in the blood.
Chromium metal is virtually non-toxic, but chromium metal dust is irritating to lung tissue. Chromium(III) compounds cause dermatitis. Chromium(VI) compounds lead to various diseases humans, including cancer. Maximum permissible concentration of chromium(VI) in atmospheric air 0.0015 mg/m3.

encyclopedic Dictionary. 2009 .

See what "chrome" is in other dictionaries:

chromium- chrome, and... Russian spelling dictionary

chromium- chrome/… Morphemic-spelling dictionary

- (from the Greek chroma color, paint). A grayish metal mined from chrome ore. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. CHROME metal of grayish color; in its pure form x. not used; connections with... Dictionary of foreign words of the Russian language

CHROMIUM- see CHROME (Cr). Chromium compounds are found in wastewater many industrial enterprises producing chrome salts, acetylene, tannins, aniline, linoleum, paper, paints, pesticides, plastics, etc. Trivalent compounds are found in water... ... Fish Diseases: A Guide

CHROME, ah, husband. 1. Chemical element, hard light gray shiny metal. 2. Kind of yellow paint (special). | adj. chromium, aya, oh (to 1 value) and chrome, aya, oh. Chromium steel. Chrome ore. II. CHROME, ah, husband. Soft variety thin skin. | adj... Dictionary Ozhegova

chromium- a, m. chrome m. novolat. chromium lat. chroma gr. dye. 1. Chemical element is a hard silvery metal used in the manufacture of hard alloys and for coating metal products. BAS 1. Metal discovered by Vauquelin... ... Historical Dictionary of Gallicisms of the Russian Language

CHROMIUM- CHROME, Chromium (from the Greek chroma paint), I symbol. SG, chem. element with at. weighing 52.01 (isotopes 50, 52, 53, 54); serial number 24, for! occupies a place in the even subgroup VI of group j of the periodic table. Compounds X. are often found in nature... Great Medical Encyclopedia

- (lat. Chromium) Cr, chemical element of group VI Periodic table Mendeleev, atomic number 24, atomic mass 51.9961. Name from Greek. chroma color, paint (due to the bright color of the Compound). Bluish silvery metal; density 7.19… … Big Encyclopedic Dictionary

CHROME 1, a, m. Ozhegov’s Explanatory Dictionary. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 … Ozhegov's Explanatory Dictionary

CHROME 2, a, m. A type of soft, thin leather. Ozhegov's explanatory dictionary. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 … Ozhegov's Explanatory Dictionary

Chrome is a refractory, very hard metal with extraordinary resistance to corrosion. These unique qualities have ensured that it is in such high demand in industry and construction.

The consumer is most often familiar not with chrome products, but with objects coated with a thin layer of metal. The dazzling mirror shine of such a coating is attractive in itself, but it also has a purely practical significance. Chrome is resistant to corrosion and can protect alloys and metals from rust.

And today we will answer questions about whether chromium is a metal or a non-metal, and if it is a metal, then what kind: black or non-ferrous, heavy or light. We will also tell you in what form chromium is found in nature, and what are the differences between chromium and other similar metals.

First, let's talk about what chromium looks like, what metals it contains, and what is special about such a substance. Chrome is a typical metal of a silvery-bluish color, heavy, superior in density, and also belongs to the category of refractory - its melting and boiling points are very high.

The element chromium is located in the secondary subgroup of group 6 in the 4th period. It is close in properties to molybdenum and tungsten, although it has noticeable differences. The latter most often exhibit only the highest oxidation state, while chromium exhibits valency two, three, and six. This means that the element forms many different compounds.

It was the compounds that gave the name to the element itself - from the Greek paint, color. The fact is that its salts and oxides are painted in a wide variety of bright colors.

This video will tell you what chrome is:

Features and differences compared to other metals

When studying metal, two properties of the substance aroused the greatest interest: hardness and refractoriness. Chromium is one of the hardest metals - it ranks fifth and is inferior to uranium, iridium, tungsten and beryllium. However, this quality turned out to be unclaimed, since the metal had properties that were more important for industry.

Chromium melts at 1907 C. It is inferior to tungsten or molybdenum in this indicator, but is still classified as a refractory substance. True, its melting point is greatly influenced by impurities.

• Like many corrosion-resistant metals, chromium forms a thin and very dense oxide film in air. The latter covers the access of oxygen, nitrogen and moisture to the substance, which makes it invulnerable. The peculiarity is that it transfers this quality to its alloy with: in the presence of the element, the potential of the a-phase of iron increases and, as a result, the steel in air is also covered with a dense oxide film. This is the secret of stainless steel's durability.
• Being a refractory substance, the metal also increases the melting point of the alloy. Heat-resistant and heat-resistant steels necessarily include a proportion of chromium, sometimes very large - up to 60%. The addition of both and chromium has an even stronger effect.
• Chromium also forms alloys with its group mates – molybdenum and tungsten. They are used to coat parts where particularly high wear resistance under high temperature conditions is required.

The advantages and disadvantages of chromium are described below.

Chrome like metal (photo)

Advantages

Like any other substance, metal has its own advantages and disadvantages, and their combination determines its use.

• The undoubted advantage of the substance is its corrosion resistance and the ability to transfer this property to its alloys. Chrome stainless steels have great value, because they simultaneously solved a number of problems in the construction of ships, submarines, building frames, and so on.
• Corrosion resistance is ensured in another way - by covering the object with a thin layer of metal. The popularity of this method is very great; today there are at least a dozen methods of chrome plating in different conditions and to get different results.
• The chrome layer creates a bright mirror shine, so chrome plating is used not only to protect the alloy from corrosion, but also to obtain an aesthetic appearance. Moreover, modern chrome plating methods make it possible to create a coating on any material - not only on metal, but also on plastic and ceramics.
• Obtaining heat-resistant steel by adding chromium should also be considered an advantage of the substance. There are many areas where metal parts must operate at high temperatures, and iron itself does not have such resistance to stress at temperatures.
• Of all refractory substances, it is the most resistant to acids and bases.
• An advantage of the substance is its prevalence - 0.02% in the earth's crust, and a relatively simple method of extraction and production. Of course, it requires energy, but it cannot be compared with a complex one, for example.

Flaws

The disadvantages include qualities that do not allow full use of all the properties of chromium.

• First of all, this is a strong dependence of physical, and not just chemical properties, on impurities. Even the melting point of the metal was difficult to establish, since in the presence of an insignificant fraction of nitrogen or carbon, the indicator changed noticeably.
• Despite its higher electrical conductivity compared to chromium, chromium is used much less in electrical engineering and its cost is quite high. It is much more difficult to make anything from it: the high melting point and hardness significantly limit its use.
• Pure chromium is a malleable metal, but when it contains impurities it becomes very hard. To obtain at least a relatively ductile metal, it has to be subjected to additional processing, which, of course, increases manufacturing costs.

Metal structure

The chromium crystal has a body-centered cubic lattice, a = 0.28845 nm. Above a temperature of 1830 C, a modification with a face-centered cubic lattice can be obtained.

At a temperature of +38 C, a second-order phase transition with an increase in volume is recorded. In this case, the crystal lattice of the substance does not change, but its magnetic properties become completely different. Up to this temperature – the Néel point – chromium exhibits the properties of an antiferromagnet, that is, it is a substance that is almost impossible to magnetize. Above the Néel point, the metal becomes a typical paramagnetic, that is, it exhibits magnetic properties in the presence of a magnetic field.

Properties and characteristics

IN normal conditions the metal is quite inert - both due to the oxide film and simply by its nature. However, as the temperature rises, it reacts with simple substances, acids, and bases. Its compounds are very diverse and are used very widely. The physical characteristics of the metal, as mentioned, strongly depend on the amount of impurities. In practice, they deal with chromium with a purity of up to 99.5%. are:

• melting temperature– 1907 C. This value serves as the boundary between refractory and ordinary substances;
• boiling temperature– 2671 C;
• Mohs hardness – 5;
• electrical conductivity– 9 · 106 1/(Ohm m). In this indicator, chromium is second only to silver and gold;
• resistivity–127 (Ohm mm2)/m;
• thermal conductivity substance is 93.7 W/(m K);
• specific heat–45 J/(g K).

The thermophysical characteristics of the substance are somewhat anomalous. At the Néel point, where the volume of the metal changes, the coefficient of its thermal expansion increases sharply and continues to grow with increasing temperature. Thermal conductivity also behaves anomalously - it drops at the Néel point and decreases when heated.

The element is among the necessary ones: in human body Chromium ions are participants in carbohydrate metabolism and the process of regulating insulin secretion. The daily dose is 50–200 mcg.

Chromium is non-toxic, although in the form of metal powder it can cause irritation to the mucous membranes. Its trivalent compounds are also relatively safe and are even used in the food and sports industries. But hexavalent ones are poisonous for humans and cause severe damage to the respiratory tract and gastrointestinal tract.

Today we will talk about the production and price of chromium metal per kg later.

This video will show you if the coating is chrome:

Production

In a large number of different minerals - often accompanies and. However, its content is not sufficient to be of industrial importance. Only rocks that contain at least 40% of the element are promising, so there are few minerals suitable for mining, mainly chromium iron ore or chromite.

The mineral is extracted by mine and quarry methods, depending on the depth of occurrence. And since the ore initially contains a large proportion of metal, it is almost never enriched, which, accordingly, simplifies and reduces the cost of the production process.

About 70% of the mined metal is used to alloy steel. Moreover, it is often used not in its pure form, but in the form of ferrochrome. The latter can be obtained directly in a shaft electric furnace or a blast furnace - this is how carbon ferrochrome is obtained. If a compound with a low carbon content is required, the aluminothermic method is used.

• This method produces both pure chromium and ferrochrome. To do this, a charge containing chromium iron ore, chromium oxide, sodium nitrate, etc. is loaded into the smelting shaft. The first portion, the ignition mixture, is set on fire, and the rest of the charge is loaded into the melt. At the end, flux - lime - is added to facilitate the extraction of chromium. Melting takes about 20 minutes. After some cooling, the shaft is tilted, the slag is released, returned to its original position and tilted again, now both chromium and slag are removed into the mold. After cooling, the resulting block is separated.
• Another method is also used - metallothermic smelting. It is carried out in an electric furnace in a rotating shaft. The charge here is divided into 3 parts, each with a different composition. This method allows you to extract more chromium, but, most importantly, reduces consumption.
• If it is necessary to obtain a chemically pure metal, they resort to a laboratory method: crystals are planted by electrolysis of chromate solutions.

The cost of chrome metal per 1 kg fluctuates noticeably, since it depends on the volume of rolled metal produced - the main consumer of the element. In January 2017, 1 ton of metal was valued at $7,655.

Application

Categories

So, . The main consumer of chromium is ferrous metallurgy. This is due to the ability of the metal to transfer such properties as corrosion resistance and hardness to its alloys. Moreover, it has an effect when added in very small quantities.

All alloys of chromium and iron are divided into 2 categories:

• low alloy– with a chromium share of up to 1.6%. In this case, chromium adds strength and hardness to the steel. If ordinary steel has a tensile strength of 400–580 MPa, then the same grade of steel with the addition of 1% of the substance will demonstrate a tensile strength of 1000 MPa;
• highly alloyed– contain more than 12% chromium. Here the metal provides the alloy with the same resistance to corrosion that it itself has. All stainless steels are called chrome because it is this element that provides this quality.

Low-alloy steels are classified as structural: they are used to make numerous machine parts - shafts, gears, pushers, and so on. The scope of use of stainless steel is huge: metal parts of turbines, ship and submarine hulls, combustion chambers, fasteners of any kind, pipes, channels, angles, sheet steel and so on.

In addition, chromium increases the alloy’s resistance to temperature: with a substance content of 30 to 66%, products made of heat-resistant steel can perform their functions when heated to 1200 C. This is a material for piston engine valves, for fasteners, for turbine parts and other things.

If 70% of chromium is used for the needs of metallurgy, then the remaining almost 30% is used for chrome plating. The essence of the process comes down to applying a thin layer of chromium to the surface of a metal object. For this purpose the most different methods, many are available to home craftsmen.

Chrome plating

Chrome plating can be divided into 2 categories:

• functional– its purpose is to prevent corrosion of the product. The layer thickness here is greater, so the chrome plating process takes longer - sometimes up to 24 hours. In addition to preventing rust, the chrome layer significantly increases the wear resistance of the part;
• decorative– chrome creates a mirror-shiny surface. Car enthusiasts and motorcycle racers rarely turn down the opportunity to decorate their car with chrome parts. The decorative layer of the coating is much thinner - up to 0.0005 mm.

Chrome plating is actively used in modern construction and in the manufacture of furniture. Fittings with a mirror finish, bathroom and kitchen accessories, kitchen utensils, furniture parts - products with a chrome finish are extremely popular. And since thanks modern method chrome plating, the coating can be created on literally any object; somewhat atypical methods of application have also appeared. For example, chrome-plated plumbing cannot be classified as a trivial solution.

Chrome is a metal with very unusual properties, and its qualities are in demand in industry. For the most part, its alloys and compounds are of interest, which only increases the importance of the metal for the national economy.

The video below will tell you about removing chrome from metal: