Holmium: the essentials
- Name: holmium
- Symbol: Ho
- Atomic number: 67
- Relative atomic mass (Ar): 164.93033 (2)
- Standard state: solid at 298 K
- Appearance: silvery white
- Classification: Metallic
- Group in periodic table:
- Group name: Lanthanoid
- Period in periodic table: 6 (lanthanoid)
- Block in periodic table: f
- Shell structure: 126.96.36.199.8.2
- CAS Registry: 7440-60-0
Holmium atoms have 67 electrons and the shell structure is 188.8.131.52.8.2. The ground state electronic configuration of neutral holmium is [Xe].4f11.6s2 and the term symbol of holmium is 4I15/2.
Holmium is relatively soft and malleable, and is stable in dry air at room temperature. It oxidises rapidly in moist air and at elevated temperatures. The metal has unusual magnetic properties. The metal is a rare earth metal found in monazite, gadolinite and other minerals.
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Holmium: physical properties
- Density of solid: 8795 kg m-3
- Molar volume: 18.74 cm3
- Thermal conductivity: 16 W m‑1 K‑1
Holmium: heat properties
- Melting point: 1734 [1461 °C (2662 °F)] K
- Boiling point: 2993 [2720 °C (4928 °F)] K
- Enthalpy of fusion: 20.5 kJ mol-1
Holmium: atom sizes
- Atomic radius (empirical): 175 pm
- Molecular single bond covalent radius: 166 (coordination number 3) ppm
- van der Waals radius: 283 ppm
- Pauling electronegativity: 1.23 (Pauling units)
- Allred Rochow electronegativity: 1.10 (Pauling units)
- Mulliken-Jaffe electronegativity: (no data)
Holmium: orbital properties
- First ionisation energy: 580.99 kJ mol‑1
- Second ionisation energy: 1136.7 kJ mol‑1
- Third ionisation energy: 2200 kJ mol‑1
- Universe: 0.5 ppb by weight
- Crustal rocks: 1200 ppb by weight
- Human: (no data) ppb by weight
Holmium: crystal structure
Holmium: biological data
- Human abundance by weight: (no data) ppb by weight
Holmium has no biological role but is said to stimulate the metabolism.
Reactions of holmium as the element with air, water, halogens, acids, and bases where known.
Holmium: binary compounds
Binary compounds with halogens (known as halides), oxygen (known as oxides), hydrogen (known as hydrides), and other compounds of holmium where known.
Holmium: compound properties
Bond strengths; lattice energies of holmium halides, hydrides, oxides (where known); and reduction potentials where known.
Holmium: historyHolmium was discovered by J. L. Soret and Delafontaine in 1878 at Switzerland. Origin of name: from the Greek word "Holmia" meaning "Sweden".
Isolation: holmium metal is available commercially so it is not normally necessary to make it in the laboratory, which is just as well as it is difficult to isolate as the pure metal. This is largely because of the way it is found in nature. The lanthanoids are found in nature in a number of minerals. The most important are xenotime, monazite, and bastnaesite. The first two are orthophosphate minerals LnPO4 (Ln deonotes a mixture of all the lanthanoids except promethium which is vanishingly rare) and the third is a fluoride carbonate LnCO3F. Lanthanoids with even atomic numbers are more common. The most comon lanthanoids in these minerals are, in order, cerium, lanthanum, neodymium, and praseodymium. Monazite also contains thorium and ytrrium which makes handling difficult since thorium and its decomposition products are radioactive.
For many purposes it is not particularly necessary to separate the metals, but if separation into individual metals is required, the process is complex. Initially, the metals are extracted as salts from the ores by extraction with sulphuric acid (H2SO4), hydrochloric acid (HCl), and sodium hydroxide (NaOH). Modern purification techniques for these lanthanoid salt mixtures are ingenious and involve selective complexation techniques, solvent extractions, and ion exchange chromatography.
Pure holmium is available through the reduction of HoF3 with calcium metal.
2HoF3 + 3Ca → 2Ho + 3CaF2
This would work for the other calcium halides as well but the product CaF2 is easier to handle under the reaction conditions (heat to 50°C above the melting point of the element in an argon atmosphere). Excess calcium is removed from the reaction mixture under vacuum.