Chemistry Lecture Notes - September 11, 2006

# Chemistry Lecture Notes - September 11, 2006 - Chemistry...

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Chemistry Lecture Notes September 11, 2006 Average atomic mass (abundance) 12.01 amu Why is it not 12.00 amu? Because the values given in the periodic tables are an average mass of all of the isotopes Carbon is 98.90% 12C (12.00000 amu) and 1.10% 13C (13.00335 amu) The weigted average is calculated like this… o (0.9890)(12.00000 amu) + (0.0110)(13.00335 amu) = 12.01 amu Av0gadro’s Number and the Molar Mass of an Element Mole (mol) – the number of atoms in exactly 12.000 g. of 12C. This is a number! o Like a dozen or gross It is experimentally determined to be equal to 6.022e23 Called Avogadro’s Number Molar mass – the mass in grams of one mole of units (atoms or molecules) So what is the molar mass of 12C? 12.000 g What is the molar mass of just carbon? 12.011 g The molar mass in grams of any element is numerically equivalent to the atomic mass in amu for one atom. Amu and molar mass = same number, different unit

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Chemistry Lecture Notes - September 11, 2006 - Chemistry...

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