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GOSSMONT CHEM 141 - Atoms and Elements

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Atoms and ElementsImaging AtomsLaw of conservation of massLaw of Constant composition (Law of Definite Proportions)Law of Multiple ProportionsAtomic TheorySub Atomic ParticlesSlide 8Slide 9Slide 10Slide 11Atoms are composed ofSlide 13Atomic Number = Z = number of protons in an atom. = number of electrons in a neutral atom.Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23IsotopesAtomic MassSlide 26Slide 27Slide 28Isotopes of NeonSlide 30Slide 31Slide 32Mole (mol)Slide 34Slide 35Slide 36Atoms and ElementsChapter 2Imaging Atoms•March 6, 1981–Scanning tunneling microscopy allowed Gerd Binnig and Heinrich Rohrer to “see” the first atoms.Heinrich RohrerThe word atom written with atoms in JapaneseGerd BinnigIndividual atomsLaw of conservation of mass•Mass is neither created nor destroyed in a chemical reaction.•In an ordinary chemical reaction, the total mass of reacting substances is equal to the total mass of products formed.Practice problems Tro – 2.4, 2.31-2.32, 2.91Law of Constant composition (Law of Definite Proportions)•Different samples of a pure chemical substance always contain the same proportion of elements by mass.•The relative amount of each element in a particular compound is always the same, regardless of the source of the compound or how it was made.Practice problems Tro – 2.5, 2.33-2.36,Law of Multiple Proportions•If two elements combine in different ways to form different substances, the mass ratios are small, whole number multiples of each other.Practice problems Tro – 2.6-2.7, 2.37-2.40, 2.113Atomic Theory•Elements (matter) is composed of small, indivisible particles called atoms.•Atoms of a given element are identical in mass and behavior.•Atoms of different elements differ in mass and behavior.•Chemical combination of elements to make different substances occurs when atoms join together in small whole number ratios.•Chemical reactions only rearrange the way the atoms are combined; the atoms themselves are not changed.Practice problems Tro – 2.8, 2.41-2.42Sub Atomic Particles•Thompson – determined charge/mass ratio for an electron.–Charge/mass = 1.758820 x 108 C/g•Millikan – determined the charge on an electron.–Charge = 1.602176 x 10-19 CLeading to the mass of an electronmass = 9.109382 x 10 -29 gAtoms are composed ofProtons + charge 1.67x10-24g nucleusNeutrons no charge 1.67x10-24g nucleusElectrons - charge 9.11x10-28g AroundnucleusPractice problems Tro – 2.12-2.15, 2.44, 2.49-2.52Atomic Number = Z = number of protons in an atom. = number of electrons in a neutral atom.Isotopes•Atoms which differ only in the number of neutrons present in the nucleus.Carbon – 12 Element nameMass NumberPractice problems Tro – 2.16-2.17, 2.53-2.58Atomic Mass•The weighted average of the isotopic masses of an element’s naturally occurring isotopes.•Atomic mass unit - amuIsotopes of Neonisotope AtomicmassNatural Abundance20Ne 19.99 90.51%21Ne 20.99 0.27%22Ne 21.99 9.22%Isotopes of NeonPractice problems Tro – 2.73-2.78, 2.108-2.109, 2.112Mole (mol)•Number of particles in atomic mass in grams of an element.•Number of molecules/formula units in the molar mass in grams of a compound• 6.02 x 1023 particles.•How many water molecules are in one drop of water? (One drop of water is 1/20 of a mL, and the density of water is 1.0 g/mL.)•How many hydrogen atoms are in a drop of water?Practice problems Tro – 2.79-2.90, 2.102-2.104, 2.106-2.107,


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