Interpreting the electron configuration of a neutral atom in noble-gas notation A neutral atom has the following e- configuration: [He] 2s 2 2p 5 Chemical symbol: F How many e-: 9 How many 2p e- in atom: 5 He with a superscript 2, + 7 = 9e- total Look for the atom w/ a p+ -> F [Ne] 3s 2 Symbol: Mg e-: 12 3s: 2 Predicting Ionic Compounds Formed by Two Elements Element One Element Two Forms Ionic Compound? Empirical Formula of Ionic Compound Sulfur Potassium yes K 2 S Magnesium Potassium no Potassium Chlorine yes KCl Sulfur Iodine no Ionic Compound = metal & nonmetal Metal element = cation Nonmetal element = anion S=metal, K=nonmetal. K usually forms a +1 cation (K + ) and S usually forms a -2 anion (S 2− ). Need the net charge to = 0 so (2K + ) -> +2 (1S 2− ) -> -2 0 Element One Element Two Forms Ionic Compound? Empirical Formula of Ionic Compound Bromine Oxygen no Rubidium Oxygen yes Rb 2 O Rubidium Strontium no Iodine Rubidium yes RbI Element One Element Two Forms Ionic Compound? Empirical Formula of Ionic Compound Cesium Chlorine yes CsCl Barium Sulfur yes BaS Sulfur Cesium yes Cs 2 S Fluorine Sulfur no Ca 2+ Cl − -> CaCl 2 Li + I − -> LiI Cs + O 2− -> Cs 2 O Cs + Cl − -> CsCl