Calculating Atomic Masses from Isotopic Composition, Lecture notes of Chemistry

Download Calculating Atomic Masses from Isotopic Composition and more Lecture notes Chemistry in PDF only on Docsity! Atomic Mass  One atomic mass unit (amu): the mass exactly equal to one-twelfth the mass of one carbon-12 atom that has six protons and six neutrons. 1 atom of carbon-12 = 12 amu 1 amu = mass of one C-12 atom 12 1 amu = 1.66054 x 10-24 g and 1 g = 6.02214 x 1023 amu  Average Atomic Mass: the weighted average of the masses of the naturally occurring isotopes of the element; the mass of the atom in atomic mass units Average Atomic Mass = ∑ (fractional abundance of isotope n) × (mass of isotope n)  Isotopes: atoms with identical atomic numbers but different mass numbers (that is, same number of protons but different numbers of neutrons) Average atomic mass of carbon = (0.09890)(12.00000 amu) + (0.0110)(13.00335 amu) = 12.0107 amu       Example If chlorine is 75.78 % Cl-35 with a mass of 34.9689 amu and the rest Cl-37 with a mass of 36.9659 amu, find chlorine’s atomic mass. Cl atomic mass = 0.7578 x 34.9689 + (1 - 0.7578) × 36.9659 = 35.45 amu              Atomic Number Atomic Symbol Atomic Weight Carbon Isotopes Atomic Number (number of protons) Mass number (number of protons plus neutrons)