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CHEM 1A03 LECTURE 2.docx

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McMaster University
David Brock

1 CHEM 1A03 LECTURE #2 September 12 2012 **iClicker for marks starts Tuesday the 18 . Oxidation numbers: ref p.85 fig 3.2 Empirical Formula: Reduces to the most common denominator of molecule. For instance, empirical formula for benzene is CH, while molecular formula is C6H 6 Molecular Formula: Actual numbers of each element are represented. Condensed Formula: Empirical formula in brackets, with common denominator on the outside. For instance, the condensed formula for benzene is (CH) 6 Isotopes: Elements which share the same # of protons, but differ in # of neutrons and therefore differ in mass #. A E Z A = Mass Number (neutrons +protons) Z = Atomic # (number of protons) Z identifies which element it is, A identifies the isotope. Isotopes have natural abundance, which means they are found in statistically uniform distributions around the world. Finding changes/trends in these distributions allow scientists to analyze changes in nature, i.e. Calibrating rainfall vs. snowfall per era in glacial deposits. 18 16 Measuring O/ O ratios in ice cores lets us ‘measure’ past world T (with data calibrated against the recent past) – evidence for global warming. September 13/14 2012 2 It’s a “climate proxy” (preserved physical characteristic of the past) Temperature Scales Kelvin is measured on the absolute temperature scale: 0K = Absolute Zero Celsius is a more traditional style, 0 C = 273K. These figures change in a 1:1 ratio. Therefore, changes in temperature have the same value, regardless of T scale. Extensive vs. Intensive Quantities Extensive properties: depend on the amount of substance involved i.e. m,V, heat (q) Intensive properties: independent of the
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