CHEM 121 Lecture Notes - Lecture 1: Chemical Equation, Mass Spectrometry, Molecular Mass

• School: Simon Fraser University
• Department: Chemistry
• Course: CHEM 121
• Professor: Steven Holdcroft

Document Summary

Dalton: beginning of modern chemistry - atomic theory. Gay-lussac: 2 molecules of h2 + 1 molecule o2 2 molecules of h2o. J. j thomson: experiments with cathode ray tubes --> discovery of electrons --> Plum pudding model (e- dispersed in positive cloud) Alpha particles: he2+ ions x7300 larger than e- Fired alpha particles into gold foil (atoms), saw some rebounded particles which proved there was a dense positive center of atoms with spaced out e- Electron cloud ~ 108 cm in diameter cm across. Chemical properties are determined by the number of valence electrons. # of protons/electrons are the same if atom is neutral. If atom is charged, # of electrons will change. Same atomic # but different mass = isotopes. Isotopes are determined by the laws of nuclear physics. Isotopes: same chemical properties, different physical properties (crucial) Elements exists as a mixture of isotopes: carbon-12 (99%) carbon-13 (1%, silicon-28 (91%), silicon-29 (5%), silicon-30 (3%), etc, bromine-79 (51%), bromine-81 (49%)