Template:Infobox thallium

Thallium,  ₈₁Tl

General properties
Name, symbol	thallium, Tl
Appearance	silvery white
Pronunciation	/ˈθæliəm/ THAL-ee-əm
Thallium in the periodic table
In ↑ Tl ↓ Uut mercury ← thallium → lead
Atomic number (Z)	81
Group, block	group 13, p-block
Period	period 6
Element category	post-transition metal
Standard atomic weight (Ar)	204.38 (204.382–204.385)
Electron configuration	[Xe] 4f14 5d10 6s2 6p1
per shell	2, 8, 18, 32, 18, 3
Physical properties
Phase	solid
Melting point	577 K ​(304 °C, ​579 °F)
Boiling point	1746 K ​(1473 °C, ​2683 °F)
Density near r.t.	11.85 g/cm3
when liquid, at m.p.	11.22 g/cm3
Heat of fusion	4.14 kJ/mol
Heat of vaporization	165 kJ/mol
Molar heat capacity	26.32 J/(mol·K)
vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 882 977 1097 1252 1461 1758
Atomic properties
Oxidation states	3, 2, 1, −1, −2, −5 ​(a mildly basic oxide)
Electronegativity	Pauling scale: 1.62
Ionization energies	1st: 589.4 kJ/mol 2nd: 1971 kJ/mol 3rd: 2878 kJ/mol
Atomic radius	empirical: 170 pm
Covalent radius	145±7 pm
Van der Waals radius	196 pm
Miscellanea
Crystal structure	​hexagonal close-packed (hcp)
Speed of sound thin rod	818 m/s (at 20 °C)
Thermal expansion	29.9 µm/(m·K) (at 25 °C)
Thermal conductivity	46.1 W/(m·K)
Electrical resistivity	0.18 µΩ·m (at 20 °C)
Magnetic ordering	diamagnetic
Young's modulus	8 GPa
Shear modulus	2.8 GPa
Bulk modulus	43 GPa
Poisson ratio	0.45
Mohs hardness	1.2
Brinell hardness	26.5–44.7 MPa
CAS Number	7440-28-0
History
Discovery	William Crookes (1861)
First isolation	Claude-Auguste Lamy (1862)
Most stable isotopes of thallium
iso NA half-life DM DE (MeV) DP 203Tl 29.524% – (α) 0.9108 199Au 204Tl syn 3.78 y β− 0.764 204Pb ε 0.347 204Hg 205Tl 70.476% – (α) 0.1567 201Au
Decay modes in parentheses are predicted, but have not yet been observed

References

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