Chapter 2: Lecture Notes
Chapter 2: Lecture Notes 110.0
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This 6 page Class Notes was uploaded by Caroline Hess on Wednesday October 14, 2015. The Class Notes belongs to 110.0 at University of Pittsburgh taught by Paul,Stanley in Fall 2015. Since its upload, it has received 32 views. For similar materials see GENERAL CHEMISTRY 1 in Chemistry at University of Pittsburgh.
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Date Created: 10/14/15
Chapter 2 Atoms Molecules and Ions 14 Law of De nite Proportions A pure compound whatever its source always contains de nite or constant proportions of the elements by mass AKA Law of Constant Composition 0 Created byJoseph Proust Example Known has 960 g of Carbon and 256 grams of oxygen What s the ratio 960g 256g I 96og 1960g 2 66 1 to 266 ratIo If you re given 810 g of carbon how many grams of oxygen are in the compound 810gx2662160g 21 Atomic Theory of Matter 0 John Dalton All elements compounds or mixtures are composed of small particles called atoms Dalton s Atomic Theory Postulates Know these 1 All matter consists of indivisible parts called atoms 0 No longer true because of electrons protons and neutrons 2 Atoms of the same element are similar in shape and mass but differ from the atoms of other elements 3 Atoms cannot be created nor destroyed 4 Atoms of different elements may combine with each other in a xed simple whole number ratios to form compound atoms 5 Atoms of same element can combine in more than one ratio to form two or more compounds 6 The atom is the smallest unit of matter that can take place in a chemical reaction 21 Law of Multiple Proportions When two elements form more than one compound the masses of one element in these compounds form a xed mass of the other element are in ratios of small WHOLE NUMBERS Example Carbon C Oxygen 02 22 The Structure of the Atom Dalton39s postulate that atoms were indivisible particles was incorrect Discovery of the Electron 0 J J Thomson and the Cathode Ray 0 Amount of de ection is dependent on Strength of magnet Charge of electron Mass of electron 0 Charge to mass ratio qm 175881O11 Ckg o The cathode ray has a negative charge because it s attracted to the positive side Independent of the metal used 0 He doesn t know what it is but he knows it s lighter than hydrogen so he thinks it s something inside the atom that is negatively charged 0 He discovers the electron and discovers the mass to charge ratio 0 Robert Millikan and the Oil Drop Experiment 0 Charge of electron 116021O3919 C 0 Mass of an electron 91091O3913 Nucleus of an Atom 0 Ernest Rutherford Gold Foil Experiment 0 1911 Proposed the nuclear model of the atom 0 Most alpha rays positively charged particles pass through the metal but a few were scattered at large angles 0 Most of the mass is concentrated in the positively charged center or nucleus around which the negatively charged electrons move Nuclear Theory of the Atom Rutherford 1 Most of the atoms mass and all of its positive charge are contained in a small core called the nucleus 2 Most of the volume of the atom is empty space throughout which tiny negatively charged electrons are dispersed 3 There are as many negatively charged electrons outside the nucleus as there are positively charged particles protons within the nucleus so the atom is electrically neutral 23 Nuclear Structure lsotopes 0 Atomic Number Z The number of protons determined the type of element 0 Mass Number A Sum of protons and neutrons determines the isotope of the element sotopes atoms who s nuclei have the same atomic number but different mass numbers 0 Same of protons but different of neutrons 17 3 CI Isotope Proton Neutro Electro 5 ns ns 3 17 18 18 1 Cl 20 18 Mass spectrum 0 Spectrometer Element is ionized Electrons are entered 24 Atomic Weights Gives the charge to mass ratio 0 All of an elements isotopes are the same size Examples 35CI 757 37CI 2423 3496885 l O75773496885 264959 369659 l O24233 Average Mass 69659 89568 26 Chemical Formulas 0 Notation that uses atomic symbols with subscripts to indicate the proportions of the elements Examples NaCl l Na1CI391 CaClz l Ca2Cl39Cl39 Molecules A group of atoms chemically bonded together tightly connected by attractive forces Diatomic Molecules Memorize H2 N2 02 F2 Clz Brz I2 Hydrogen Nitrogen Oxygen Fluorine Chloride Bromine Iodine lonic Substances lon Electronically charged particle obtained from and atom or chemically bonded group of atoms by adding or removing electrons m Negatively charged ion Cation Positively charged ion lonic Compound Composed of cations and anions o Metals and nonmetals Examples 1 Charges Al3 Protons 13 Electrons10 Neutrons NA Mg2 Protons12 Electrons10 Neutrons NA Cl39 Protons 17 Electrons18 Neutrons NA Need isotope to nd 29 Writing Chemical Equations Reactants Products Put physical A s B2 g l AB s State Mg s 02 g n M90 is l 210 Balancing Chemical Equations Mg 02 I Mgo Not Balanced 2 Mg 02 I 2 M90 39 Balanced Example Tetrahydrogen dinitrade decomposes to form trihydrogen nitrate and nitrogen gas H4N2 I H3N N2 H4N2 g D H3N g N2 9 3 H4N2g D 4 H3N g N2 9
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