Chem 1120 1st Edition Lecture 19 Outline of Last Lecture I Solubility Equilibria II 4 Factors Affecting Solubility a Common Ion Effect b pH c Presence of Complexing Agents d Amphoterism III Precipitation and Separation of Ions Outline of Current Lecture I Periodic Trends and Classes of Elements II Group 1A 1 Hydrogen Current Lecture I Although we went over trends last semester we are going to review them this chapter and go more in depth with them now As you go across the periodic table Increasing Ionization Energy Decreasing Atomic Radius Increasing Electronegativity Decreasing Metallic Character As you go down the periodic table Decreasing Ionization Energy These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Increasing Atomic Radius Decreasing Electronegativity Increasing Metallic Character Classes of Elements Metals majority of periodic table good conductors of heat and electricity mostly positive oxidation numbers and except for Hg solids in their standard state Metalloids properties of both metals and nonmetals many are semiconductors B Si Ge As Nonmetals poor conductors of heat and electricity both positive and negative oxidation numbers common noble elements are gases at standard state Br2 is a liquid Non metallic elements only 17 out of 114 life is based on them C O H N P S negative oxidation states when combined with metals can have positive oxidation states in bonding to other non metals higher electronegativities than the metals nonmetal oxides are acidic combine with water to give oxy acids Ionization Energy minimum energy needed to remove an electron from a gaseous atom A or ion endothermic trend above Electron Affinity negative of enthalpy for electron gain by atom A smaller than ionization energy exothermic except for noble gases and alkaline earth elements Electronegativity tendency of an atom in a molecule to gain additional electron density while retaining its original electron density Within a group smaller atoms are more likely to form pi bonds because they can get closer to other atoms overlap more II Group 1A 1 Hydrogen Hydrogen is very common but unique at the sea time It makes up 75 of the mass of the universe 11 of the mass of the oceans 0 15 of the Earth s crust 0 4 of the mass of the atmosphere 9 5 of the mass of a human body Hydrogen has three isotopes Hydrogen should not really belong to any group it is unique in its electron configuration and is the only element with an unfilled 1s valence shell that can either gain or lose an electron Ionic hydrides 3 hydride types are good reducing agents there are Ionic hydrides Metallic hy drides Covalent hy drides organic com pounds are covalent hydrides Molecular hydrides formed between hydrogen and nonmetals or metalloids usually gases or liquids at room temperature and normal atmospheric pressure stability of the nonmetal hydrides decreases down the group Properties of Hydrogen very large bond enthalpies reacts slowly at room temperature forms strong bonds with other elements its reactions are generally quite exothermic forms H bonds with electronegative O F and N strong intermolecular forces H bonds are fundamental to life i e proteins DNA Hydrogen Fuel Cells using hydrogen as a fuel would have many advantages its reaction with water is highly exothermic water is the only product problem how will we make the H2 Hydrogen production hydrogen is commercially produced from reaction of methane with steam at 1100 degrees C or carbon and steam above 1100 degrees C its production from the electrolysis of water is not efficient energy Hydrogenation addition of dihydrogen to multiple bonds usually Carbon double bonds and triple bonds