Compounds containing poly atomic ions Patrons for poly atomic ions Na Single ions that contain more than one atom Often identi ed by parentheses around ion in formula Name and charge of poly atomic ions do not change Elements in same column form similar poly atomic ions Same number of O s and same charge ClO3 chlorate BrO3 bromate Hydrates Hemi 1 2 Mono 1 Pre x and number of waters Di 2 Tri 3 Ionic compounds containing a speci c number of waters for each formula nit Water of hydration often driven off by heating Tetra 4 Penta 5 Hexa 6 Hepta 7 Octa 8 In formula attached waters follow Pre x Name if 1st element Pre x Base name of 2nd element IDE Writing names of binary molecular compounds of two nonmetals Acids Molecular compounds that form H when dissolved in water To indicate the compound is dissolved in water aq is written after the formula Sour taste Dissolve many metals such as Zn Binary acids contain on y two elements Oxyacids contain oxygen Naming binary acids Hydro pre x Nonmetal name Change ending on nonmetal name to ic Naming oxyacids If poly atomic ion name ends in ate then change ending to ic suf x If poly atomic ion name ends in ite then change ending to ous suf x Write word acid at end of all names Hints for writing formulas for acids When name ends in acid formulas starts with H Write formulas as if ionic even though it is molecular Hydro pre x means it is binary acid no pre x means it is an oxyacid For oxyacid if ending is ic polyatomic ion ends in ate if ending is ous polyatomic ion ends in ite Calculations Why is it important to know the formula of a compound SO you know the number of atoms of each element To follow law of conservation of matter How do I use the mole concept to perform calculations How does the PT help in calculations conversion factor Mass number moles number particles Masses of all atoms Formula mass Mass of an individual molecule or formula unit Aka molecular mass or molecular weight Sum of the masses of the atoms in a single molecule or formula unit Molar mass of compounds 1 mole of h2o contains 2 moles of h and 1 mole of o so molar mass 1 mole h2o Examples 1 how many moles are in 50 0 g of PbO2 Pb 207 2 O 16 00 2 Find the number of CO2 molecules in 10 8 g of dry ice 3 How many formula units are in 50 0 g of PbO2 4 What is the mass of 4 78 x 10 24 NO2 molecules Percent composition Examples 1 Find the mass percent of Cl in C2Cl4F2 Percentage of each element in a compound by mass May not always total to 100 due to rounding Percentage part whole x 100 2 Determine the mass percent composition of CaCl2 Mass Percent as Conversion Factor The mass percent tells you the mass of a constituent element in 100 g of the compound Empirical Formula Simplistic whole number ratio of the atoms of elements in a compound Can be determined from elemental analysis Masses of elements forms when a compound is decompose or that react together to form a compound Combustion analysis Percent composition Finding an empirical formula 1 2 3 4 5 Use molar mass of each element Assume you start with 100 g of the compound Convert percentages into grams A Convert grams into moles A Write a pseudo formula using moles as subscripts Divide all by smallest number of moles A Multiply all mole ratios by number to make all whole numbers A B C If ratio 0 5 multiply all by 2 If ratio 33 or 67 multiply all by 3 Skip if already whole numbers If result is within 0 1 of whole number round to whole number Molecular Formulas Chemical reactions A multiple of the empirical formula Molar mass of molecular formula molar mass empirical formula Reactions involve chemical changes in matter resulting in new substances Responsible for combustion reactions and reactions of acids and metals