Sept. 8 Lecture Chemical formulas express the composition of molecules and ionic compounds using chemical symbols - molecular formulas indicate the number of each type of atom in the smallest unit of a substance - empirical formulas give ratios of atoms in the compound in the most reduced form e.g. sugar (glucose) molecular formula = C6H12O6 empirical formula = CH2O - structural formulas are drawings that show how the atoms are bonded e.g. benzene molecular formula = C6H6 empirical formula = CH structural formula H | C H C || H C C | H C H | C H Can determine charges of many ions from their position on the periodic table: (+1) (+2) (+3) (-3) (-2) (-1) transition metals have multiple possible charges Naming compounds Ionic compounds made up of cations and anions held together by ionic bonds - can be monatomic (consisting of one atom: H+, O2-, ...) or polyatomic (NH4+, OH-, ...) 1) When writing formulas/names of ionic compounds, cation comes first 2) For binary ionic compounds (compounds of just 2 elements), name the cation, then name the anion but replace its ending with "-ide" NaCl sodium chloride (chlorine becomes chloride) KBr potassium bromide 3) When naming compounds containing transition metal cations that can have multiple possible charges (e.g. Fe2+, Fe3+; Mn2+, Mn3+, Mn4+), put the charge in Roman numerals in parentheses after the name of the cation FeO iron(II) oxide (the charge on oxygen is -2, so the iron must be +2 to balance it and form a neutral compound) Fe2O3 iron(III) oxide (there are 3 oxygens, each with a -2 charge, giving a -6 total negative charge for all the oxygens; there must be a +6 total charge among all of the iron atoms to balance this, but there are 2 iron atoms, so each one has a +3 charge) 3) For compounds containing polyatomic ions, simply name the ...