- •Chrome subgroup physical properties
- •Chrome subgroup trends
- •History Of Discovery
- •Occurrence
- •Preparation
- •Electronic Configurations & Oxidation States
- •Chemical Properties. Free Chrome And Compounds (0)
- •Low oxidation states
- •Compounds e(IV)
- •Compounds e(V)
- •Questions and tasks
- •Make up the equations o f the reactions Make up the equations of the reactions
- •Experimental section
- •2. Chemical properties of chrome
- •3. Chemical properties to molybdenum and tungsten
- •Chrome. Standard electrode potentials, eo, V
- •Mendeleev's predicted elements
- •The Pourbaix diagram for chrome in pure water, perchloric acid or sodium hydroxide
- •M olybdenum Wheels
- •From Recent Developments in Inorganic Chemistry 2005
Course Curriculum |
Module 1 |
Module 2 |
Module 3 |
Module Exams |
Final Exam |
Labs |
Questions & tasks |
handbook |
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The Periodic table |
s-elements |
p-elements |
d-elements |
Fotogallery |
Video |
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Chrome [Ar]3d54s1 E lectronic configurations |
Chrome |
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lab |
Home tasks |
Quiz |
Video |
photos |
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Properties Of Chrome |
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Chemical |
Physical |
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Uses |
Occurrence |
Preparation |
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History Of Discovery |
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Chrome subgroup trends |
Electrode potentials |
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Cr (Ox.State) |
Compounds Of Chrome. Chemical And Physical Properties Overview |
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-3 (d9) |
…. |
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-2 (d8) |
Na2[Cr(CO)5] |
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-1 (d7) |
Na2[Cr2(CO)10] |
Na2[Mo2(CO)10] |
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0(d6) |
Cr(C65H6)2 |
Mo(CO)6 |
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+1 (d5) |
K3[Cr(CN)5NO] |
Na[C6H6Mo] |
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+2 (d4) |
CrCl2 |
MoCl2
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WCl2 |
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+3(d3) |
CrCl3 |
Na3[Mo(CN)]6 |
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+4(d2) |
K2CrF6 |
MoS2 |
WO2 |
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+5(d1) |
K3CrO8 |
MoCl5 |
WCl5
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+6(d0) |
K2CrO4 |
MoF6 |
WO3 WCl6 K2WO4 |
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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
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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.