Chem I Final Exam Study Guide Compound a substance composted of atoms of TWO or more elements chemically united in fixed proportions Element A substance that cannot be separated into simpler substances by chemical means Element 1 unit Compound 2 or more elements Physical properties mass volume malleability temperature boiling point melting point etc Chemical properties combustibility oxidation rusting etc density mass volume F 9 5 C 32 C 5 9 F 32 K C 273 15 Sig fig rules 1 any digit that is not zero is significant 2 3 4 5 zeros between non zero digits are significant zeros to the left of the first nonzero digit are not significant if a number is 1 all the zeros to the right of the decimal are significant If a number is 1 only the zeros that are at the end of the number and the zeros that are between non zero digits are significant Electrons were discovered by a cathode ray when 2 electrically charged plates and a magnet are added to the outside of the cathode ray tube it was discovered that the cathode ray is attracted by the plate bearing chargers and repelled by the plate bearing charges using magnetic and electric fields Electrons therefore must consist of negatively charged particles In Millikan s experiment he examined the motion of single tin drops of oil that picked up static charge from ions in the air Millikan suspended the charged drops in air by applying an electric field and followed their motions through a microscope With his knowledge of electrostatics he found the charge to be 1 6022 10 19 C of an electron Alpha particles positive and largest Beta partials negative Gamma particles no charge smallest Rutherford used thin foils of gold and metals as targets for alpha particles from a radioactive source He found that most of the particles were undeflected but sometimes alpha particles were deflected at a large angle or even bounced back He explained this for happening b c most of the atom is empty space which is why they were not deflected Whenever an alpha particle was close to the nuclei containing a charge it bounced back Protons deflected by positively charged plates Neutrons no charge not affected Electrons deflected by negatively charged plates Isotopes atoms that have the same atomic number but different mass numbers different number of neutrons Ex Uranium 235 is used for atomic bombs and Uranium 238 lacks properties needed for a bomb Mass number of protons and neutrons Atomic number of protons Electrons same number as protons 1H protium 1 pro 1 electron 2H deuterium 1 pro 1 electron 1 neutron 3H tritium 1 pro 1 electron 2 neutrons Naturally occurring diatomic molecules H2 N2 O2 F2 Cl2 Br2 I2 Monatomic ions contain only 1 atom ex Mg2 Fe3 S2 Polyatomic ions 2 or more atoms ex OH CN Cation an ion with a net positive charge Anion An ion whose net charge is negative Molecular formula shows the exact number of atoms of each element in the smallest unit of a substance ex N2H4 Empirical formula which elements are present in the simplest whole number ratio of their atoms not necessarily the actual number of atoms ex NH2 For ionic compounds to be electrically neutral the sum of the charges on the cation and anion in each formula unit must be zero Potassium Bromide K and Br KBr Zinc Iodide Zn2 and I ZnI2 Aluminum Oxide Al3 and O2 Al2O3 Naming molecular compounds binary compounds of non metals usually metalloids 1 Use prefixes for both elements present mono prefix is omitted for first element 2 Add ide to the root of the second element Naming ionic compounds If the cation only has one charge you name the metal first and then the anion If the cation has more than one charge you specify the charge of the cation using roman numerals in parentheses with the anion following it All monatomic ions end in ide ex Bromide chloride fluoride Naming acids contain hydrogen and an anionic group Anions that usually end in ide bond to Hydrogen atoms forming an acid The ide changes to ic and the term hydro is put in the front ex H and S2 hydrosulfuric acid Naming oxoacids acids containing hydrogen oxygen and another element central element Reference acids Naming bases same as naming molecular compounds First ten alkanes Meredith Eats Purple Bugs 1 Methane CH4 2 Ethane C2H6 3 Propane C3H8 4 Butane C4H10 5 Pentane C5H12 6 Hexane C6H14 7 Heptane C7H16 8 Octane C8H18 9 Nonane C9H20 10 Decane C10H22 amu a mass equal to 1 12 the mass of 1 carbon 12 atom 1 amu 1 661 10 24 g atomic numbers on the table of elements are measured in amu Calculating average atomic mass 100 mass 100 mass Ex Atomic masses of 6Li and 7Li are 6 0151 amu and 7 0160 amu The average atomic mass is 6 941 amu What is the natural abundance of each 6 941 6 0151x 7 0160 1 x x 0741 x 926 6Li 7 4 7Li 92 6 of objects present in a given of moles 6 022 E 23 objects Avogadro s number mass moles mass g molar mass g mol moles number of atoms moles Avogadro s number molar mass g mol molecular mass amu Percent composition Mass percent Mass of an atom Total mass 100 Example H in H2SO4 2 016 amu 98 086 amu 100 2 06 24 75 by mass K 34 77 by mass Mn and 40 51 by mass O convert to moles 633 mol K 633 mol Mn 2 53 mol O Given the Composition of the atoms in a compound we can get the empirical and molecular formula Ex 1 2 Divide each number of moles by smallest number of moles in this case 633 moles 3 K 1 Mn 1 O 4 4 Empirical formula KMnO4 5 For molecular formula we need the molar mass molar mass empirical mass 6 Then multiply the subscripts by that number Balance chemical equations KClO3 KCl O2 2KClO3 2KCl 3O2 Mass g Moles mol Molecules mol Avogadro s number Reactants left of arrow Products right of arrow Stoichiometry 1 Write a balanced equation 2 Convert the given amount of the reactant g to number of moles 3 Use the mole ratio from the equation to calculate the number of moles of product formed 4 Convert the moles of the product to grams of product Finding theoretical yield and percent yield 1 Find limiting reagent 2 Use the limiting reagent to find the mass formed 3 This mass is the theoretical yield 4 To find percent yield actual yield theoretical yield 100 Calculating the required mass for each reactant given percent yield and mass of desired products 1 Find theoretical yield actual yield percent decimal form 2 Use backwards stoichiometry to find mass of reactant Solution homogenous mixture of two or more substances Solute present in smaller amounts of a solution Solvent present in larger amounts of a solution Strong electrolytes ionic
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