Atomic Theories. Atomic timeline Your poster should contain: –The date the theory was developed –A picture of the ‘model’ –The name of the main contributor.

  • Published on
    31-Dec-2015

  • View
    216

  • Download
    4

Embed Size (px)

Transcript

  • Atomic Theories

  • Atomic timelineYour poster should contain:The date the theory was developedA picture of the modelThe name of the main contributorA short summary of the theory

  • Atomic Timeline450 BC1803189619101911

  • 450 BC - DemocritusSaid that matter is composed of tiny, indivisible particles called atomosAtom (2006): Smallest part of an element that still has the property of that elementI was close enough. You little punks living in your AD dont know how good you have it.

  • 1803 John DaltonThe theory that atoms are the fundamental building blocks of matter reemerged in the early 19th centuryJohn Dalton: School teacher Based on observations of how elements combine

  • 1803 John DaltonBasically summarized what was already said in his Top Five Descriptions of Matter

    Haha, thats like my top ten list that I do everynight..except its the top 5 and its about matter. I get it.1. Elements are composed of extremely small particles called atoms2. All atoms of an element are identical in mass & properties3. Atoms of one element are different from atoms of another element4. Atoms of an element are not changed into atoms of another element; nor are they created or destroyed in chemical reactions5. Compounds are formed when atoms combine; a given compound always has the same relative number & kind of atoms

  • Daltons Table of Elements

  • Daltons PostulatesLaw of Constant Composition (was known at the time)In a compound, the relative #s and kinds of atoms stay the same5. Compounds are formed when atoms combine; a given compound always has the same relative number & kind of atomsLaw of Conservation of Mass (was known at the time)The total mass of materials present after a chemical reaction is the same as the total mass present beforeMassreactants = MassProducts4. Atoms of an element are not changed into atoms of another element; nor are they created or destroyed in chemical reactionsLaw of Multiple Proportions (Dalton predicted!)If two elements A and B combine to form more than one compound, they do so in simple whole number ratios

  • J.J. Thomson The Cathode Ray TubeDiscovered negatively charged part of an atomThis was the first Sub Atomic particleWas able to use his cathode ray tube to determine Charge:Mass ratio

  • J.J. Thomsons ModelElectrons were small mass, so they must be small size compared to the atomExplain where the electrons were located in his Plum Pudding ModelUniform positive sphere with electrons embedded

  • Millikans Oil Drop ExperimentRobert MillikanDetermined the charge of an electronUsed this & Thomsons charge:mass ratio to determine the massMass e- = 9.10 x 10-28 g

  • Rutherfords Gold Foil

  • Rutherford (and his gold foil)RutherfordGold Foil ExperimentAtom is mostly empty space (how empty?)Nucleus: Contains all of the mass (neutrons and protons)Electrons: Account for most of the volume

  • QuestionsWhy do things have different mass?

    Why does this happen?

  • Modern Atomic Theory2 Problems with Daltons Theory

    Atoms are divisibleAtoms of an element can be different

  • Subatomic ParticlesProton: Discovered by Rutherford in 1919Charge: 1.602 x 10-19 CNeutron: Discovered by James Chadwick in 1932Charge: 0Electron: (J.J.) Charge: -1.602 x 10-19 C

    1 amu = 1.66054 x 10-24 g

  • Identifying AtomsAtomic number:# of protons in the nucleusAddress of the atom identifies what element it isAtomic Weight:Average mass of the atomMass NumberThe number of protons + neutrons in the nucleusWhole #Why dont we count electrons?1836 Electrons = mass of 1 proton

  • Using these numbersAtomic # = # of protons = # of electronsMass # = protons + neutronsNeutrons = Mass # - protons

  • ExamplesDetermine the number of P+, No, and E- inMgAtomic # = 12 12protons, 12electronsMass # = 24 12 neutronsTcAtomic # = 43 43protons, 43electronsMass # = 99 56 neutronsMnAtomic # = 25 25protons, 25electronsMass # = 55 30 neutronsSnAtomic # = 50 50protons, 50electronsMass # = 119 69 neutrons

  • Chemical Symbols

  • a.Cannot determine number of electrons without additional information.The atom has 30 electrons.The atoms has 15 electrons. The atom has no electrons unless it is charged.

  • a.Cannot determine number of electrons without additional information.The atom has 30 electrons.The atoms has 15 electrons. The atom has no electrons unless it is charged.

  • b.The protons reside in the nucleus of the atom. The protons are evenly distributed throughout the atom.The protons are dispersed with the electrons around the nucleus.The protons reside in a shell just outside the nucleus.

  • b.The protons reside in the nucleus of the atom. The protons are evenly distributed throughout the atom.The protons are dispersed with the electrons around the nucleus.The protons reside in a shell just outside the nucleus.

  • Modern Atomic Theory2 Problems with Daltons Theory

    Atoms are divisibleAtoms of an element can be different

  • IsotopesAtoms of the same element with different #s of neutrons

    D:\Chapter_02\Present\eMedia_Library\HydrogenIsotopes\HydrogenIsotopes.html

  • Average Atomic MassIsotopes in Bananas

    19K39.098

  • Relative AbundanceTo calculate average mass, we must know how much each isotope occursCalculating Average:(mass isotope 1 x %) + (mass isotope 2 x %) +.

  • A hypothetical element has two isotopes. One of the isotopes has an abundance of 75.0% and a relative mass of 12.0 amu, while the other has an abundance of 25.0% and a relative mass of 14.0 amu. The atomic mass of this hypothetical element is 12.5 amu.13.0 amu.13.5 amu.13.8 amu.

  • Correct Answer:Atomic mass = (0.750)(12.0 amu) + (0.250)(14.0 amu)Atomic mass = 9.0 amu + 3.5 amu = 12.5 amu12.5 amu.13.0 amu.13.5 amu.13.8 amu.

  • PRACTICE EXERCISEThree isotopes of silicon occur in nature: 28Si (92.23%), which has an atomic mass of 27.97693 amu; 29Si (4.68%), which has an atomic mass of 28.97649 amu; and 30Si (3.09%), which has an atomic mass of 29.97377 amu. Calculate the atomic weight of silicon.Answer:28.09 amu

  • IonsAtoms of the same element with different #s of electrons

  • Solution (a) Magnesium has atomic number 12, and so all atoms of magnesium contain 12 protons and 12 electrons. The three isotopes are therefore represented by (b) The number of neutrons in each isotope is the mass number minus the number of protons. The numbers of neutrons in an atom of each isotope are therefore 12, 13, and 14, respectively.PRACTICE EXERCISEGive the complete chemical symbol for the atom that contains 82 protons, 82 electrons, and 126 neutrons.

  • How many neutrons are there in an atom of 14C?681214

  • Correct Answer:Atomic numberMass number146CThe difference between the mass number and the atomic number is the number of neutrons (14 6) = 8.681214

  • An isotope of Cr3+ ion containing 24 protons and 27 neutrons would contain ___ electrons.2124273

  • Correct Answer:The +3 charge indicates there are 3 more protons than electrons: 24 3 = 212124273

Recommended

View more >