Difference between revisions of "Holmium"

Revision as of 23:06, 26 December 2017

Holmium,  ₆₇Ho

General properties
Name, symbol	Holmium, Ho
Appearance	Soft, silvery white metal
Holmium in the periodic table
- ↑ Ho ↓ Es Dysprosium ← Holmium → Erbium
Atomic number	67
Standard atomic weight (Ar)	164.93033(2)
Group, block	, f-block
Period	period 6
Electron configuration	[Xe] 4f11 6s2
per shell	2, 8, 18, 29, 8, 2
Physical properties
Silvery-white
Phase	Solid
Melting point	1734 K ​(1461 °C, ​2662 °F)
Boiling point	2873 K ​(2600 °C, ​4712 °F)
Density near r.t.	8.79 g/cm3
when liquid, at	8.34 g/cm3
Heat of fusion	17 kJ/mol
Heat of	251 kJ/mol
Molar heat capacity	27.15 J/(mol·K)
pressure
Atomic properties
Oxidation states	3, 2, 1 ​(a basic oxide)
Electronegativity	Pauling scale: 1.23
energies	1st: 581 kJ/mol 2nd: 1140 kJ/mol 3rd: 2204 kJ/mol
Atomic radius	empirical: 176 pm
Covalent radius	192±7 pm
Miscellanea
Crystal structure	​Hexagonal close-packed (hcp)
Speed of sound thin rod	2760 m/s (at 20 °C)
Thermal expansion	11.2 µm/(m·K) (poly)
Thermal conductivity	16.2 W/(m·K)
Electrical resistivity	8.14·10-7 Ω·m (poly)
Magnetic ordering	Paramagnetic
Young's modulus	64.8 GPa
Shear modulus	26.3 GPa
Bulk modulus	40.2 GPa
Poisson ratio	0.231
Vickers hardness	410–600 MPa
Brinell hardness	500–1250 MPa
CAS Registry Number	7440-60-0
History
Discovery	Jacques-Louis Soret (1878)
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Holmium is a lanthanide with the atomic number 67 and the symbol Ho. It is a gray metal that is reactive and slightly magnetic at room temperature. Holmium is difficult to find and somewhat expensive, but has some interesting properties regarding its magnetism and narrow absorption bands.

Properties

Physical properties

As a lanthanide, holmium resembles is neighboring elements strongly. It is paramagnetic, enough to be visibly lifted by a neodymium magnet. Its trivalent salts show dramatic color changes depending on the light source: they appear yellow in natural daylight, but vividly pink under compact fluorescent lighting, and very slightly pink under tube lighting.

Chemical properties

Holmium is a strong reducing agent and will readily react with weak oxidizers. It burns in air with a yellow or green flame to form holmium oxide. (The green color is likely the true color of burning holmium; the yellow color may be black-body radiation from the products.) Holmium is almost exclusively trivalent, and it is extremely difficult to reduce or oxidize holmium salts. It also reacts with the halogens to form colorful halides, which have the same color-changing properties under different light sources.

Holmium carbonate may form a soluble complex, but can be broken by addition of hydrogen peroxide.

Holmium trifluoroacetate and holmium trifluoromethanesulfonate (triflate) are relatively recently discovered catalysts for organic reactions. Even though they are Lewis acids, they do not hydrolyze readily and can be used in numerous solvents. Other lanthanide triflates have been investigated for catalytic activity.

Availability

Holmium is more common than iodine on Earth, but it is very hard to find. For a lanthanides, it is cheaper than some other metals. One source for holmium, as well as other rare earth metals, is Metallium. It is sold in 5 gram and 50 gram sizes, as well as rods, ampoules, and coins. Holmium and its compounds are occasionally sold on eBay as well.

Isolation

Holmium can be obtained by reducing holmium salts, like holmium(III) chloride, with calcium metal in a thermite-like reaction.

Projects

• Make holmium compounds
• Color changing crystals.
• Magnet polepieces?

Safety

Storage

Bulk holmium metal is stable in air indefinitely. As a powder or fine turnings, it may be extremely flammable, and should be kept away from ignition sources.

Toxicity

Holmium and its compounds have not been thoroughly investigated for toxicity, but no adverse effects have been reported from exposure.

Flammability

Small pieces of holmium metal or powder are flammable. Class D fire extinguishers should be readily available when working with large amounts of holmium near an open flame. Water should never be used to extinguish burning holmium, as it will aggravate the flame.

Disposal

Due to holmium's rarity, it's best to recycle it.

References

• flickr.com/photos/37388341@N00/2696039566/in/photostream/
• flickr.com/photos/37388341@N00/2381429226/

Relevant Sciencemadness threads

• An experiment on holmium corrosion
• Magnetic properties of holmium