Analytical testing dots

Thulium is a chemical element that has the symbol Tm and atomic number 69. A lanthanide element, thulium is the least abundant of the rare earths. It is an easily workable metal with a bright silvery-gray luster and can be cut by a knife. It has some corrosion resistance in dry air and good ductility. Naturally occurring thulium is made entirely of the stable isotope Tm-169.


Name, Symbol, Number thulium, Tm, 69
Chemical series lanthanides
Group, Period, Block n/a, 6, f
Appearance silvery gray
Standard atomic weight 168.93421(2) g·mol-1
Electrons per shell 2, 8, 18, 31, 8, 2
Physical properties
Phase solid
Density (near r.t.) 9.32 g·cm−3
Liquid density at m.p. 8.56 g·cm−3
Melting point 1818K
(1545°C, 2813°F)
Boiling point 2223K
(1950°C, 3542°F)
Heat of fusion 16.84 kJ·mol-1
Heat of vaporization 247 kJ·mol-1
Heat capacity (25°C) 27.03 J·mol-1·K-1
Vapor pressure
P(Pa) 1 10 100 1 k 10 k 100 k
at T(K) 1117 1235 1381 1570 (1821) (2217)
Atomic properties
Crystal structure hexagonal
Oxidation states 3
(basic oxide)
Electronegativity 1.25 (Pauling scale)
Ionization energies
1st: 596.7 kJ·mol-1
2nd: 1160 kJ·mol-1
3rd: 2285 kJ·mol-1
Atomic radius 175 pm
Atomic radius (calc.) 222 pm
Magnetic ordering no data
Electrical resistivity (r.t.) (poly) 676 nΩ·m
Thermal conductivity (300K) 16.9 W·m-1·K-1
Thermal expansion (r.t.) (poly)
13.3 µm/(m·K)
Young's modulus 74.0 GPa
Shear modulus 30.5 GPa
Bulk modulus 44.5 GPa
Poisson ratio 0.213
Vickers hardness 520 MPa
Brinell hardness 471 MPa
CAS registry number 7440-30-4


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Analytical testing dots

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