CH Chapter 1
CH Chapter 1 CH 101
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This 4 page Class Notes was uploaded by rebecca goodrich on Friday January 22, 2016. The Class Notes belongs to CH 101 at University of Alabama - Tuscaloosa taught by Paul Rupar in Fall 2015. Since its upload, it has received 16 views. For similar materials see General Chemistry in Chemistry at University of Alabama - Tuscaloosa.
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Date Created: 01/22/16
CH 101 Chapter 1 notes Law of definite proportions ratio of mass and quantity will always be the same Ex. 40 g of CO2 is made up of 12 g of carbon. How much oxygen is present? What is the ratio of oxygen to carbon. 40g= total mass 40 g12 g carbon leaves 28 g oxygen 28 O/ 12 g C = 7:3 John Dalton (17661844) Elements are made up of atoms All atoms of an element are the same An atom cannot be created or destroyed Compounds are made of atoms in whole number ratios During a reaction atoms separate and recombine Charges Positive and negative charges (opposite attract), Like charges repel JJ Thomson and the cathode Ray Tube - Glass tube containing metal electrodes from which almost all the air has been evacuated - When connected to a high voltage power supply a glowing area is seen emanating from the cathode - The beam is deflected by external charges and magnets - The cathode rays are made of tiny particles o Negatively charged particles because the were deflected towards the positive plate - Every material contains these particles - Calculated the mass charge ratio of these particles o Charge mass ratio= 1.76*10^9 C.g - The charge was the same as hydrogen ion - If the particle has the same amount of charge as a hydrogen ion then the mass has almost 2000x smaller than hydrogen atoms - Particles are pieces of atoms / a part of atoms - Thomson “discovered” the electron Mulligan oil drop experiment - Used to determine what the charge of an electron was - Small drops of oil were suspended within a chamber - As the drops of oil fell through the air they were negatively charged by ionizing radiation - Mulligan applied an electric field to stop the oil drops from falling - By knowing the mass of the oil drops and the strength of the electric Field, milikan could measure the amount of charge on the drops - He calculated the mass of the oil drops through the assumption that the drops were perfect spheres and therefore the volume is 4/3 pi r^3 - The charge of each drop was always a multiple of 1.60 *10^19 C - The charge of e Charge always comes in welldefined packs Quantification of physics Found the mass of the electron was 9 *10^28 g Electrons Electrons are tiny negatively charged particles All atoms are made from electrons The electron has a charge of 1.6*10^19 C The electron has a mass of 9.1*10^28g The cathode rays are made of streams of Electrons Review Normal matter is not charged and atoms are not charged Normal matter contains small particles called electrons Why are atoms not negatively chared? there must be positively charged particles countering the reaction Plum Pudding Model of the Atom JJ Thomson - There is a positively charged sphere surrounded - First model of the atom to suggest physical parts - Atoms have inner structure Background - Alpha particles are positively charged particles emitted by some radioactive materials o 8000 times heavier than e Rutherford gold foil Experiment - Rutherford shot alpha particles through gold foil and studied the reaction o A few alpha particles are deflected and others would go through o 98% of the alpha particles went strait through o 2% were deflected at large angles o 0.005% bounced off - Conclusions Most alpha particles travel though because atoms and matter are empty space o A few of the alpha particles deflect/ bounce o Therefore there must be something very small, very dense, that is positively charged o The atom contains a dense center called the nucleus o The center of the atom o The nucleus is 10^11 times smaller than the atom o Most of the mass of the atom is in the nucleus o The nucleus is positively charged – balancing the electrons o The electrons are in the empty space surrounding the nucleus o He concluded that the nucleus is made of protons o The protons are positively charged o The charges of protons are equal and opposite to that of electrons Atomic Mass A. Many elements have multiple, stable isotopes B. The ratio of different isotopes within a sample is constant a. Ex. Chlorine: has 2 common isotopes 35 cl and 37 cl i. CL is 75.77% abundant, 37 CL is 24.33 abundant ii. CL 35 has 17 pt, because it has 17 on periodic table, 18 neutrons because 35117 C. We calculate the average of the isotopes to determine the atomic mass of an element a. Formula for atomic mass= the sum of (fractional abundance of isotope)n * (mass of isotope)n b. Ex. The exact mass of 35 Cl is 34.97 anu and the exact mass of 37 CL is 36.67 amu. What is the atomic Mass of Chlorine? i. Atomic Mass = (.7577)(34.97)+ (.2433)(36.67)= 35.42 amu Mass Spectrometry - There are many different ways for a scientist to measure the mass of an isotope - A mass spectrometer can measure the mass of atoms and molecules - A mass spectrometer works by moving ions past magnets and measuring how much the ions are deflected by the magnets - Lighter ions are deflected more by the magnets o Heavier ions are deflected less - A mass spectrum is a graph that gives the relative mass and relative abundance of each particle - Relative mas of the particle is plotted on the x axis - Relative abundance of the particles is plotted on the y axis Why use mass spectrometry? - TO determine isotopic ratio - Measuring the mass of molecules o Can be applied to proteins - Commonly used in forensic analysis - Commonly used in medical diagnostics
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