Elements Group 16 Elements { { The Chalcogens { { All group elements are solids except oxygen oxygen, sulfur, and selenium = nonmetals tellurium = metalloid polonium = metal Amanda Runge Meghan Estochen Mark Humberstone Physical Properties OXYGEN Selected Properties Covalent radius/pm O S Se Te Po 74 104 117 137 140 Ionic radius/pm 140 184 198 221 First Ionization energy (kJ/mol) 1310 1000 941 870 812 Melting point/ºC -218 113 217 450 254 Boiling point/ºC -183 445 685 990 960 3.5 2.5 2.4 2.1 2 141 200 195 190 183 Pauling Electronegative Electron Affinity (kJ/mol) 1 OXYGEN { { OXYGEN Oxygen, the most abundant element of the group, is found as two allotropes, dioxygen (O2) and ozone (O3). Dioxygen‘s ground state is triplet oxygen as well as a state of higher energy, singlet oxygen. Triplet State OXYGEN { { { { { Electrons and charged particles that are given off by the sun can hit triplet state oxygen, exciting it into the singlet state. When the electron falls back to the ground state, visible light is emitted, producing the Aurora Borealis. Colors seen are determined by the altitude and energy at which the collisions between particles and electrons are taking place Particles = 1000 – 15000 eV Occurs at poles because charged particles are channeled by Earth’s magnetic field lines which go into the poles Singlet State OXYGEN { { It is the second most electronegative element in periodic table, making it the most reactive of the group. The high electronegativity of oxygen leads to polarity in bonding. z { i.e. Hydrogen-Bonding in water The oxidation state of oxygen is -2. The lack of d-orbitals makes it difficult for higher states. 2 SULFUR SULFUR { { Sulfur is commonly found as an 8-membered ring. Poor pi-orbital overlap due to larger atomic size hinders double bonding with itself. It can form stable compounds with oxidation states ranging between -2 and +6. Its most common states are -2, +4, and +6. This is due to the availability of d-orbitals. SULFUR { Sulfur forms a similar structure with hydrogen as it does with oxygen, but the differences in electronegativity make H2S less polar and therefore less likely to hydrogen bond. SULFUR { { { Sulfur was the basis for mustard gas, a cancer causing weapon used in World War I. By changing the structure of the gas and substituting nitrogen for sulfur, N-mustard is used to fight Hodgkin’s Disease and many types of cancer. Sulfur is also a component found in stink bombs usually in the form of H2S. 3 Mustard Gas { { { SULFUR SELENIUM & TELLURIUM N-mustard Sulfur was the basis for mustard gas, a cancer causing weapon used in World War I. By changing the structure of the gas and substituting nitrogen for sulfur, N-mustard is used to fight Hodgkin’s Disease and many types of cancer. Sulfur is also a component found in stink bombs usually in the form of H2S. SELENIUM & TELLURIUM { { { Selenium and tellurium are both large metalloids with similar properties. They exhibit oxidation states similar to sulfur that also range from -2 to +6. Their commonly found structures are different. Selenium is found as an 8-membered ring (like sulfur) and tellurium crystallizes in a chain-like form. SELENIUM & TELLURIUM { { Selenium and tellurium combine with most elements although not as readily as the more electronegative members of the group, oxygen and sulfur. Selenium exhibits both photovoltaic and photoconductive actions and therefore is used in the production of photocells and solar cells. 4 POLONIUM POLONIUM { { Polonium, a radioactive element, is rarely found in nature. It’s made in small quantities by a nuclear reaction with bismuth. There are 29 known radioisotopes and more known isotopes than any other element. 209 83 POLONIUM { { { Polonium crystallizes in a cubic structure. Due to large atomic size, Pi orbital overlap becomes difficult, therefore rarely forms double bonds. Following the trend, it’s the least electronegative of the group, yet combines directly with most elements. Bi + 11n → 210 84 Po + e− POLONIUM { { { In November 2006, a 210 84 Po Russian spy named Alexander Litvinenko was poisoned with a lethal dose of 210Po. Less than a microgram was responsible for his death. Po decayed through alpha emission, heavily damaging vital organs. → 206 82 Pb + 4 2 α 5 SOURCES { { { Atkins and Shriver. Inorganic Chemistry. New York: W.H. Freeman and Company, 2006. Holland, Rebecca. “Molecule of the Month." Mustard Gas. Bristol University. 4/10/07 <http://www.bristol.ac.uk/Depts/Chemistry/MOT M/mustard/mustard.htm>. WebElements™, the periodic table on the WWW, URL: http://www.webelements.com/ Copyright 1993-2007 Mark Winter [The University of Sheffield and WebElements Ltd, UK]. All rights reserved. Document served: Tuesday 10th April, 2007 6