General Chem 101 - Chapter 1
General Chem 101 - Chapter 1 CH 101
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This 3 page Class Notes was uploaded by Rebecca de la O on Monday September 5, 2016. The Class Notes belongs to CH 101 at University of Alabama - Tuscaloosa taught by Jared Allred in Fall 2016. Since its upload, it has received 79 views.
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Date Created: 09/05/16
CHAPTER 1: ATOMS Matter = stuff Pure substance = one type of Mixture = more than one particle particle Element = Compound = Heterogeneous = Homogenous = cannot be Can be separated Uniform Not uniform separated (water) (wet sand) (tea) (helium) The Scientific Approach - Hypothesis is a tentative interpretation of explanation of an observation - A scientific law summarizes past observations and predicts future ones - A scientific theory explains how and why nature works the way it does. It is formed by various hypothesis’ Early Ideas - Leucippus & Democritus first proposed matter was comprised of small indestructible parts - Plato & Aristotle said substances were comprised of different things Law of Conservation of Mass - Total mass stays the same - Except when converted into energy Law of Definite Proportions - A single substance always has the same ratio of masses - Ex. A) 19.22 g of SO2 9.60 g of O 9.62 g of S ratio = 9.60: 9.62 1:1.002 B) 83.28 g of SO2 41.60 g of O 41.68 g of S ratio= 41.60:41.68 1:1002 Law of Multiple Proportions - Fixed ratio of elements go into making two pure compounds made from the same element - Ex. NO 2 0.3045 g of N 0.6955 g of O 0.3045: 0.6955 1:2.282 NO 0.4312 g of N 0.4925 g of O 0.43.12: 0.4925 1:1.142 Dalton Atomic Theory - Atoms combine in whole number ratios to form compounds - Atoms don’t change from original, only their arrangement changes - Each element is comprised of tiny, indestructible particles - All atoms of an element are identical to each other and different from atoms of another elements Cathode Ray Tube - JJ Thomson’s experiment - Observed a beam of particles travel from the negatively charged electrode (the cathode) to the positively charged one (the anode) - Found that cathode rays travel in a straight line - Found that the particles are independent of the composition of material from the cathode - Found the charge to mass ratio of electrons Millikan Oil Drop Experiment - This experiment established the charge and mass of an electron - The measured charge for an electron is always a whole number multiple of -1.60 x 10 -1C - The mass of an electron is 9.10 x 10 -28g Rutherford Gold Foil Experiment - Directed alpha particles at a very thin sheet of gold, expecting the alpha particles to shoot straight through. Instead, some were deflected. - Most of the positive charge of the atom is located in a tiny nucleus in the center - Disproved the “Plum Pudding model” (electrons were scattered in a sphere of positive charge) Rutherford’s Atomic Model: Nuclear Atom Model - Most or all of the positive charge is in the center of the nucleus - Volume is filled by tiny negatively charged electrons - Number of electrons balances the positive charge of the nucleus Neutrons - Discovered by James Chadwick - q= 0 mass of neutrons = mass of protons - nuclear force holds protons and neutrons together - have zero charge Ions - Two nuclei with the same number of protons but different number of neutrons are isotopes - if no isotope is specified, it might be a natural combination or is unknown A - Z X 271mass number z= atomic number X= elemental symbol - Ex. 110 Ds atomic mass = 271 protons = 110 Electrons = 110 Neutron = 271=110 = 161 Summary - All matter is made of particles, whose structure determines the matters properties - We classify matter based on its state and/or composition - Every element is made up of indestructible atoms - Atoms have an electron cloud plus a nucleus (protons and neutrons) - Mass and other properties distinguish elements - Atoms cannot change into other atoms, but can change the way they are bound to other atoms (through a chemical reaction) to make a new substance - Number of protons = number of electrons (in a neutral atom) - Number of protons tells you the type of element - Nuclear mass is > 99% of total mass - The mass of an element is the weighted average of the masses of the naturally occurring isotopes of that element and can be determined through mass spectrometry