What kind of element is chrome

chrome

Chromium - the 'colored' among the chemical elements because of its colorful compounds - is a silvery white, in pure form tough, flexible, malleable, crystallizing in a body-centered cubic lattice, with the chemical symbol Cr and the atomic number 24.

Chromium is one of the few metals that can passivate: Metallic chromium reacts spontaneously with the oxygen in the air and forms a very thin oxide layer that protects the metal from further corrosion. This surface is hard, non-reactive and - as known from chrome - can be polished to a high gloss. This makes chromium ideal for electroplating other metals to protect them from oxidation, and because of its hardness, it is used for hardening and chrome plating the surface of many objects - such as furniture. B. Metal Tools - used.

 

Overview: general data on chrome

 

The Cr atom - and thus the chemical element chromium - is clearly defined by the 24 positively charged protons in the atomic nucleus. The same number of electrons ensures the electrical balance in the uncharged chromium atom.

The nuclear building blocks of the neutrons ensure that there are differences between the atomic nuclei. These types of atoms are under the term Chromium isotopes or chromium nuclides (isotope data: see there).

The earthly chromium deposits consist of an isotope mixture; the relative atomic mass is therefore given as 51.9961 u.

 

Electron configuration

symbolOZshort form1s2s2p3s3p3d4s4p4d4f
Cr24[Ar] 3d5 4s12262651

 

Ionization energies

The following table lists the binding energies or the ionization energies IE, i.e. the required energy in electron volts (eV) to separate a specific electron from a chromium atom.

1. IE: 6.76651 eV2. IE: 16.4857 eV3. IE: 30.96 eV4. IE: 49.16 eV5. IE: 69.46 eV6. IE: 90.6356 eV
7. IE: 160.18 eV8. IE: 184.7 eV9. IE: 209.3 eV10. IE: 244.4 eV11. IE: 270.8 eV12. IE: 298.0 eV
13. IE: 354.8 eV14. IE: 384,171 eV15th IE: 1010.6 eV16. IE: 1097 eV17th IE: 1185 eV18th IE: 1299 eV
19th IE: 1396 eV20th IE: 1496 eV21st IE: 1643 eV22nd IE: 1721.4 eV23rd IE: 7481.4 eV24th IE: 7894.87 eV

 

Electron binding energy

The following table lists the electron binding energies of the individual chromium electrons in the respective orbitals. The values ​​are given in electron volts (eV).

KLILIILIII
1s2s2p1/22p3/2
5989696583,8574,1

 

MIMIIMIIIMIVMV
3s3p1/23p3/23d3/23d5/2
74,142,242,2

 

Further data

 

Spectral lines of chromium

The following figure shows an emission spectrum of chromium with the characteristic spectral lines in the visible wavelength range between 400 and 700 nm:

 

 

Chromium is a member of Group 6 of the transition metals. Metallic chromium Cr (0) has the irregular electron configuration [Ar] 3d due to the lower energy of the high-spin configuration5 4s1 - instead of 3d4 4s2. It thus has six valence electrons that actually form bonds in a wide range of oxidation states; the states +3 and +6 occur most frequently in chromium compounds. Chromium charges of +1, +4 and +5 are rare and rarely encountered.

The chromium cation with the positive charge 3 (Cr3+) is the most stable ionic state of chromium.

 

Chemical data

 

Standard potentials

Normal potential of chromium:

E.0 (V)NoxName Ox.Ox.e-Red.Name Red.Nox
-0,74+ IIIChromium (III) cationCr3++ 3 e-Cr (s)chrome0
-0,42+ IIIChromium (III) cationCr3++ e-Cr2+Chromium (II) cation+ II
1,33+ VIDichromate anionCr2O72- + 14 H.++ 6 e-2 Cr3+ + 7 H.2OChromium (III) cation+ III

 

Material and physical properties of chromium

The following overview lists some physical data and material properties of the pure chromium metal.

 

Chromium shows in elemental form and paramagnetic properties. Recently, however, it was discovered that chromium can have different magnetic properties depending on its temperature, which affects the orientation of the electrons. Chromium compounds such as chromium dioxide are considered to be ferromagnetic. The ferromagnetic properties of these compounds allow them to be used in data tapes to store information.

 

Geochemistry, occurrence, distribution

Chromium ranks 13th among the abundance of chemical elements in the earth's crust with an average concentration of 102 ppm. Chromium compounds are formed in the environment through the erosion of rocks containing chromium and can be redistributed through volcanic eruptions. Typical background concentrations of chromium in environmental media are: atmosphere <10 ng m-3 ; Soil <500 mg kg-1; Vegetation <0.5 mg kg-1; Fresh water <10 μg L.-1 ; Sea water <3 μg L.-1; Sediments <80 mg kg-1.

With the exception of a diamond deposit in Russia, chromium only occurs in the form of compounds and not in elemental form. The reason for the exception is seen in the reducing environment of the diamond deposit.

 

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Category: Chemical elements

Updated on 21.01.2020.

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