Course Curriculum

Module 1

Module 2

Module 3

Module Exams

Final Exam

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handbook

The Periodic table

s-elements

p-elements

d-elements

Fotogallery

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Chrome [Ar]3d54s1 E lectronic configurations

Chrome

lab

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Properties Of Chrome

Chemical

Physical

Uses

Occurrence

Preparation

History Of Discovery

Chrome subgroup trends

Electrode potentials

Cr (Ox.State)

Compounds Of Chrome. Chemical And Physical Properties Overview

-3 (d9)

….

-2 (d8)

Na2[Cr(CO)5]

-1 (d7)

Na2[Cr2(CO)10]

Na2[Mo2(CO)10]

0(d6)

Cr(C65H6)2

Mo(CO)6

+1 (d5)

K3[Cr(CN)5NO]

Na[C6H6Mo]

+2 (d4)

CrCl2

MoCl2

WCl2

+3(d3)

CrCl3

Na3[Mo(CN)]6

+4(d2)

K2CrF6

MoS2

WO2

+5(d1)

K3CrO8

MoCl5

WCl5

+6(d0)

K2CrO4

MoF6

WO3 WCl6 K2WO4

Chrome subgroup physical properties

Chrome, molybdenum, and tungsten are hard (they can scratch glass), lustrous metals. The melting point of chrome is 1890 °C and its density is 7.19 g/cm³. However, the melting point of tungsten (about 3400 °C) is the highest among metals. The density of this heavy white metal is 19.3 g/cm³.

The presence of admixtures strongly influences the mechanical properties of metals, e.g. technically pure chrome is one of the hardest metals whereas chrome of high purity has plasticity.

Like other d-elements, the melting and boiling points, densities display growth down the chrome subgroup. In addition, radii of molybdenum and tungsten, especially E⁶⁺ ionic radii, are close to one another due to the phenomenon of lanthanide contraction. The stronger contraction the stronger attraction of the outermost shell electrons to its own atomic nucleus as well as the larger ionisation energy, and standard electrode potentials (see table below). It is worth noting that chrome subgroup metals are corrosion-resistant owing to the very dense and inert surface oxide film formation in spite of negative electrode potentials.

Chrome is remarkable for its magnetic properties: it is the only elemental solid which shows antiferromagnetic ordering at room temperature (and below). Above 38 °C, it transforms into a paramagnetic state.

Chrome subgroup trends

Chrome subgroup trends

	Cr	Mo	W
density, g/сm3	7,19	10,22	19,35
tm, oС	1890	2620	3420
tb, oС	3390	4830	5900
Rа, nm	0,127	0,137	0,140
radius Е6+, nm	0,035	0,065	0,065
Ionisation energy Е ® Е+, еV	6,77	7,10	7,98
Еo(Е3+ + 3е = Е), V	-0,744	-0,20	-0,15

History Of Discovery

The name “chrome” derived from the Greek word meaning “colour”.

Chrome was discovered in 1797 by the French chemist Nicolas-Louis Vauquelin and isolated as a metal one year later. He investigated crocoite mineral and produced chrome oxide through its reaction with HCl. The heating of chrome oxide with charcoal as a reducing agent in a furnace (the process called “smelting”) was used to obtain metallic chrome itself.

The main natural compound of molybdenum is molybdenite MoS₂. In 1778, Carl Scheele showed that when molybdenite is reacted with nitric acid, a white residue is obtained having the properties of an acid. He called it molybdic acid and concluded that the mineral itself is the sulfide of a new element. Five years later, the element was obtained in the free state by roasting molybdic acid with charcoal.

In 1781, Carl Scheele discovered new element tungsten in white mineral tungsten that was later called scheelite, CaWO₄. In 1556, Georguis Agricola (1494-1555) referred to the existence of a mineral lupi spuma (wolf’s foam; in German wolf rahm), known today as wolframite FeWO₄. The origin of this name was due to the apparent tin “eating” during the extraction, like the wolf eats the sheep.