F 9 5 C 32 K C 273 15 Atomic number number of protons is on the bottom Mass number average atomic mass is on the top CALCULATE AVERAGE MASS Average atomic mass abundance as fraction 1 mass 1 abundance as fraction 2 mass 2 Always convert abundance to a fraction Ionic Compounds strong bonds high melting and boiling points hard brittle solids good conductors of electricity between metal and non metal Molecular Covalent Compounds weak intermolecular forces low melting and boiling points liquid gas at room temperature poor conductors of electricity between two non metals use di tri petra penta to name FORMULA MASS number of atoms 1 atomic mass in periodic table number of atoms 2 atomic mass in periodic table PERCENT BY MASS Find the atomic mass for each element and multiply it by how many times the element appears in the compound KBH4 H appears 4 times so do 4 x 1 008 amu This gives the total amount of the substance then take the formula mass total amount of the substance 4 x 1 008 53 9403 0 0747 7 475 EMPIRICAL FORMULA Change the into g amu Then change amu to molar mass it s the same number but g mol Then use unit convertor and change g to mol o Take the molar mass and divide it by the atomic mass o 26 68 g C x 1 mol C 12 01g C Do this for each element Divide number of moles present by smallest number of moles present of any element to get the ratio o CHO2 Caffeine has molecular formula C8H10N4O2 find empirical formula Divide each by least common denominator in this case it s 2 MOLECULAR FORMULA Multiply each element by 6 Simplify as much as possible MOLAR MASS number of atoms 1 x atomic mass of atom 1 number of atoms 2 x atomic mass of atom 2 number of atoms 3 x atomic mass of atom 3 number of atoms 4 x atomic mass of atom 4 WHAT IS THE MASS Find the atomic mass of all the elements involved Calculate formula mass multiply amount of elements by atomic number and add them together Multiply the formula mass by the moles they give you ex What is the mass of 1 18 mol calcium oxide HOW MANY MOLES CONTAIN MOLECULES How many moles of CO2 contain 2 87 1024 molecules Change molecules to Moles o 1 mol CO2 6 02214199 1023 molecules CO2 o 1 mol CO2 6 02214199 x 1023 molecules CO2 Multiply the given number of molecules by this conversion factor divide because top of conversion factor is one WHAT NUMBER OF MOLES IS EQUIVALENT TO ATOMS OF Hg Change number of atoms to moles 1 mol of Hg 6 022 x 1023 atoms Hg multiply number of atoms it gives you by this conversion factor HOW MANY MOLECULES OF XYLOSE C5H10O5 ARE PRESENT IN 21 5g OF THE SUBSTANCE Calculate formula mass of compound 150 130 amu Find the molar mass 150 130 g mol Calculate the number of moles of substance present o 21 5g C5H10O5 x 1 mol C5H10O5 150 130 g o 0 1432 mol Use avogadro s number and number of moles of fructose to unit convert o 0 1432 mol x 6 022 x 1023 molecules 1 mol C5H10O5 o 0 86e 22 STOICHIOMETRIC COEFFICIENTS Find common number and divide by that 2 SrCl2 2H2SO4 2SrSO4 4 HCl SrCl2 H2SO4 SrSO4 2 HCl 1 cm3 1mL WHEN CONVERTING MOL TO g USE ATOMIC MASS MOLECULES TO MOL USE 6 02214199 X 1023 CALCULATE NUMBER OF MOLES PRESENT Take amount given to you Multiply by 1 mol atomic mass Do this for each element ABUDNANCE PERCENTAGE OF ISOTOPES Mass of first isotope x mass of second isotope 1 x then use algebra to find x