Thallium

Thallium,  ₈₁Tl

General properties
Appearance	sillery white
Staundart atomic wecht (Ar, staundart)	[7002204382000000000♠204.382, 7002204385000000000♠204.385] conventional: 7002204380000000000♠204.38
Thallium in the periodic cairt
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Airn Cobalt Nickel Capper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Siller (element) Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercur (element) Thallium Leid (element) Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Ununtrium Flerovium Ununpentium Livermorium Ununseptium Ununoctium In ↑ Tl ↓ Uut mercur ← thallium → lead
Atomic nummer (Z)	81
Group	group 13 (boron group)
Period	period 6
Element category	post-transition metal
Block	p-block
Electron confeeguration	[Xe] 4f14 5d10 6s2 6p1
Electrons per shell	2, 8, 18, 32, 18, 3
Pheesical properties
Phase (at STP)	solit
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
Spectral lines
Miscellanea
Creestal 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
Bouk modulus	43 GPa
Poisson ratio	0.45
Mohs haurdness	1.2
Brinell haurdness	26.4 MPa
CAS Nummer	7440-28-0
History
Diskivery	William Crookes (1861)
First isolation	Claude-Auguste Lamy (1862)
Main isotopes o thallium
Iso­tope Abun­dance Hauf-life (t1/2) Decay mode Pro­duct 203Tl 29.524% - (α) 199Au 204Tl syn 3.78 y β− 204Pb ε 204Hg 205Tl 70.476% - (α) 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.