6 atomic # C symbol Carbon name of element atomic mass. o Examples: # 1 mol C = g # 1 mol O = g # 1 mol H = 1.

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1 7.1 AVOGADRO S NUMBER AND MOLAR CONVERSIONS CHEMISTRY NOTES Identify the mole as the unit used to count particles, whether atoms, ions, or molecules. Use Avogadro s number to convert between amount in moles and number of particles. Solve problems converting between mass, amount in moles, and number of particles using Avogadro s number and molar mass. Standards: 3b,c,d MOLE The number of carbon atoms in g The SI base unit used to measure the amount of a substance whose number of particles is the same as the number of atoms of carbon in exactly 12 grams of carbon-12. CONVERTING GRAMS!" MOLES OF ATOMS o Use the periodic table to make gram to mol conversions. 6 atomic # C symbol Carbon name of element atomic mass o Examples: # 1 mol C = g # 1 mol O = g # 1 mol H = 1.01 g CONVERTING GRAMS!" MOLES OF MOLECULES o Use the periodic table and use the average atomic mass to determine the molar mass # Molar mass the mass in grams in mole of a substance o Use the molar mass to make a gram to mol conversion. o Examples: # 1 mol of C = g => g/mol = molar mass # 1 mol CO 2 = g 1 x C = 1 (12.01) = x O = 2 (16) = g/mol = molar mass # 1 mol H 2 O = g 2 x H = 2(1.01) = x O = 1 (16) = g/mol = molar mass AVOGADRO S NUMBER = x The number of particles in 1 mole x (the number of atoms/molecules/ions/forumula units/particles) in 1.00 mol CONVERTING MOL!" ATOMS o 1 mol = x atoms o to be used for single elements # C # N # O CONVERTING MOL!" MOLECULES o 1 mol = x molecules o to be used for a group of nonmetals (molecules) # CO 2 # H 2 O

2 CONVERTING MOL!" IONS o 1 mol = x ions o to be used for ions (charged atoms) # Na + # O 2 CONVERTING MOL!" FORMULA UNITS o 1 mol = x fu o to be used for ionic comounds (salts) # NaCl # K 2 O CONVERTING GRAMS!" MOLES!" ATOMS/MOLECULES/IONS/FORMULA UNITS o Use the molar mass to convert to and from grams and moles. o Use Avogadro s number to convert to and from moles and atoms/molecules/formula units.

3 7.2 RELATIVE ATOMIC MASS AND CHEMICAL FORMULAS CHEMISTRY NOTES Use a periodic table or isotopic composition data to determine the average atomic masses of elements. Infer information about a compound from its chemical formula. Determine the molar mass of a compound from its formula. Standards: 3c,d, IE1e AVERAGE ATOMIC MASS The weighted average of the masses of all naturally occurring isotopes of an element. o Isotopes atoms of the same element but with different number of neutrons and mass. Average atomic mass unit: amu (atomic mass unit) Is not a whole number because it is the average mass of all the isotopes for a given element. CALCULATING AVERAGE ATOMIC MASS Use the information about each isotope. o Atomic mass of each isotope. o The percent abundance of each isotope. # Divide by 100 and convert to a decimal Multiply each atomic mass of each isotope with the abundance decimal and add all the isotopes information to get the average atomic mass. FORMULAS Use subscripts to indicate how many atoms of each in a molecule/compound. Example: o A 2 B 3 # Two A s # Three B s

4 7.3 FORMULAS AND PERCENT COMPOSITION CHEMISTRY NOTES Determine a compound s empirical formula from its percentage composition. Determine the molecular formula or formula unit of a compound from its empirical formula and its formula mass. Calculate percentage composition of a compound from its molecular formula or formula unit. Standard: 3d PERCENT COMPOSITION The percentage by mass of each element in a compound. Helps verify a substance s identity. Can be used to compare the ratio of masses. DETERMINING PERCENT COMPOSITION o Find the molar mass of the compound. o Find the molar mass of each element or ion. o Divide the molar mass of each element by the total molar mass of the compound. o Multiply each by 100 to get a percentage of each element. # Example: Finding the percent composition of CO 2 1 x C = 1 (12.01) = x O = 2 (16) = g/mol = molar mass 1 x C = 1 (12.01) = / (100) = 27.30% C 2 x O = 2 (16) = 32 / (100) = 72.70% O ~100% EMPIRICAL FORMULAS Simplest ratio formula. Cannot be reduced. DETERMINING EMPIRICAL FORMULAS o Determine the moles of each element. o Determine which number of moles is the smallest. o Divide the moles of each element by the smallest number of moles. o Each division will produce a whole number. o The whole number indicates how many atoms of each type of atom in a compound contains. o Use subscripts to indicate how many atoms of each element in a compound. o Subscripts must be whole numbers. # If the whole number ends with..999 = round it to the next whole number.5 => multiply the entire formula by two.3 => multiply the entire formula by three MOLECULAR FORMULAS A formula that shows the number and kinds of atoms in a molecule, but not the arrangement of the atoms. Whole number multiple of the empirical formula. Can be reduced to give the empirical formula, but it is possible that the molecular formula is the same as the empirical formula o A 4 B 2 (molecular formula) = A 2 B (empirical formula) o A 2 B 2 (molecular formula) = AB (empirical formula) o A 5 B 6 (molecular formula and empirical formula)

5 DETERMINING MOLECULAR FORMULAS o Given: empirical formula and the experimental molar mass of the molecular formula (formula mass) o Determine the empirical formula if not given. o Calculate the molar mass of the empirical formula. o Using the molar masses of both the empirical formula and molecular formula, find n. # n = experimental molar mass (given) / molar mass of empirical formula o Use n to find the molecular formula with the following equation: # MF = n (EF)