Thallium

Thallium,  ₈₁Tl

General properties
Name, seembol	thallium, Tl
Appearance	sillery white
Pronunciation	/ˈθæliəm/ THAL-ee-əm
Thallium in the periodic cairt
In ↑ Tl ↓ Uut mercur ← thallium → lead
Atomic nummer (Z)	81
Group, block	group 13, p-block
Period	period 6
Element category	poor metal
Staundart atomic wicht (±) (Ar)	204.38(1)
Electron configuration	[Xe] 4f14 5d10 6s2 6p1
per shell	2, 8, 18, 32, 18, 3
Pheesical properties
Phase	solid
Meltin pynt	577 K ​(304 °C, ​579 °F)
Bylin pynt	1746 K ​(1473 °C, ​2683 °F)
Density near r.t.	11.85 g/cm3
when liquid, at m.p.	11.22 g/cm3
Heat o fusion	4.14 kJ/mol
Heat o vapourisation	165 kJ/mol
Molar heat capacity	26.32 J/(mol·K)
vapour pressur 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 (mildly basic oxide)
Electronegativity	Pauling scale: 1.62
Atomic radius	empirical: 170 pm
Covalent radius	145±7 pm
Van der Waals radius	196 pm
Miscellanea
Crystal structur	​hexagonal close-packed (hcp)
Speed o soond 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 µ Ω·m (at 20 °C)
Magnetic orderin	diamagnetic
Young's modulus	8 GPa
Shear modulus	2.8 GPa
Bulk modulus	43 GPa
Poisson ratio	0.45
Mohs haurdness	1.2
Brinell haurdness	26.4 MPa
CAS Nummer	7440-28-0
History
Discovery	William Crookes (1861)
First isolation	Claude-Auguste Lamy (1862)
Maist stable isotopes o thallium
iso NA hauf-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 predictit, but hae nae yet been observed

Thallium is a chemical element wi seembol Tl an atomic nummer 81. This saft gray poor metal is nae foond free in naitur. When isolated, it resembles tin, but discolors when exposed tae air. Chemists William Crookes an Claude-Auguste Lamy discovered thallium independently in 1861, in residues o sulfuric acid production. Baith uised the newly developed method o flame spectroscopy, in which thallium produces a notable green spectral line. Thallium, frae Greek θαλλός, thallos, meanin "a green shuit or twig," wis named bi Crookes. It wis isolatit bi electrolysis a year later, bi Lamy.