CAS CH 101 Lecture 2: Amu u, Isotopes, the Mole
20 Sep 2015
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Ch101 - lecture 2 - amu u, isotopes, the mole. 1 u: 1/12 mass of 1 atom of 12c. Exactly 12g of 12c contains na = 6. 02214 x 1023 atoms. Therefore, mass of one 12c atom is. 12g / na = 1. 99265 x 10-23 g. So, 1 u = (1/12) (1. 99265 x 10-23 g) = 1. 66054 x 10-24 g. Isotopes: elements with different numbers of neutrons. Relative atomic weight: average mass of isotopes in a sample of an element. Mass spectra: used to find the mass of isotopes. Plot of the relative abundance of charged particles v. the ratio of mass to charge (m/z) (1) strips away electron (2) accelerates positive ions (3) ions are deflected in the magnetic field. Magnetic field is adjusted to confirm detection of the ions at the end of the chamber. Relative peak height on mass spectra indicates isotope abundance.
