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Structure of the Atom

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Chapter 4: Structure of the Atom 4.1 Early theories and 4.2 Defining the atom Historical Background: Models of the Atom: -see reference chart (On Pg. 10 of your ... – PowerPoint PPT presentation

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Title: Structure of the Atom


1
Chapter 4
  • Structure of the Atom

2
4.1 Early theories and 4.2 Defining the atom
  • Historical Background
  • Models of the Atom -see reference chart
  • (On Pg. 10 of your packet)

3
4.1 Early theories and 4.2 Defining the atom
4
4.1 Early theories and 4.2 Defining the atom
  • 1. Atomists and Democritus
  • Greeks approx 2,500 years ago
  • Matter was made up of atoms? atomos or
    Indivisible particles
  • Seashell experimentbroken into smaller smaller
    pieces

5
4.1 Early theories and 4.2 Defining the atom
  • 2. John Dalton
  • 1766-1844 returned to theory of atoms
  • Atoms are like billiard balls (solid spheres)
    which cannot be broken down further
  • 4 major postulates
  • 1) All elements are composed of atoms
  • 2) Atoms of the same element are identical
  • 3) Atoms can physically mix or chemically combine
    in simple whole number ratios
  • 4) Reactions occur when atoms separate, join, or
    rearrange

6
4.1 Early theories and 4.2 Defining the atom
  • 3. William Crookes
  • developed Crookes tube (CRT) in 1870s
  • first evidence for existence of electrons because
    you could see electrons flow and confirm their
    existence.
  • tube is precursor to todays TV picture tubes

7
4.1 Early theories and 4.2 Defining the atom
  • 4. J.J. Thomson
  • discovered electron in 1897
  • discovered positively charged particles
    surrounded by electrons
  • found the ratio of the charge of an electron to
    its mass to be 1/1837

8
4.1 Early theories and 4.2 Defining the atom
  • 4. J.J. Thomson

9
4.1 Early theories and 4.2 Defining the atom
  • 4. J.J. Thomson
  • cathode ray tube experiments advancement of
    Crookes tube
  • plum-pudding model

10
4.1 Early theories and 4.2 Defining the atom
  • 5. Ernest Rutherford
  • Discovered nucleus (dense core of atom) in 1911
  • Gold foil experiments
  • Quote from E.R.s Lab Notebook
  • It is about as incredible as if you had fired a
  • 15-inch shell at a piece of tissue paper and it
    came back and hit you. -ER

11
4.1 Early theories and 4.2 Defining the atom
Video Clip Rutherford Gold Foil Experiment
12
4.1 Early theories and 4.2 Defining the atom
  • 6. Robert Milliken
  • Oil drop experiment
  • determined the charge and mass of an electron
  • Video Clip Milliken Oil Drop Experiment

13
4.1 Early theories and 4.2 Defining the atom
  • 7. James Chadwick
  • discovered the neutron (no charge, but same mass
    as proton)
  • Neutrons help disperse the strong repulsion of
    positive charges
  • Relative Sizes
  • Nucleus diameter 10-5 nm
  • Atom diameter 10-1 nm
  • Nucleus basketball --gt Atom 6 miles wide!

14
4.1 Early theories and 4.2 Defining the atom
  • 8. Niels Bohr
  • improved on Rutherfords work
  • planetary model- positive center is surrounded
    by electrons in defined orbits circling the center

15
4.1 Early theories and 4.2 Defining the atom
  • defined the following
  • energy level the location where an electron is
    found at a set distance from the nucleus
    dependent on the amount of energy it has
  • ground state the typical energy level where an
    electron is found lowest energy
  • excited state an energy level higher than the
    ground state for an electron temporary condition

16
4.1 Early theories and 4.2 Defining the atom
  • 9. Quantum Mechanical Model
  • Erwin Schroedinger Mathematical model
  • Electron locations are based on probability
  • Electrons are not particles, but waves!
  • http//phet.colorado.edu/en/simulation/hydrogen-at
    om
  • Defined
  • Orbital region where an electron is likely to
    be found 90 of the time

17
4.3 How atoms differ
  • Atoms vocabulary and classifications
  • Atom the smallest particle of matter that
    retains its properties.
  • can see individual atoms with a scanning
    tunneling microscope.

18
4.3 How atoms differ
  • Subatomic particles the component parts of an
    atom proton, neutron, and electron

19
4.3 How atoms differ
  • Ion- atom with the same number of protons but a
    different number of electrons.
  • If the atom has a () charge it has fewer
    electrons than protons, If the atom has a (-)
    charge it has more electrons than protons.

20
4.3 How atoms differ
Subatomic Particle Mass and Abbreviation Charge Location Discoverer
Proton 1 amu, p 1 Nucleus None
Neutron 1 amu, n 0 Nucleus Chadwick in 1932
Electron Almost zero, e- -1 Electron cloud Thomson
21
4.3 How atoms differ
  • Calculations involving Subatomic Particles
  • atomic number of protons
  • mass number of protons of neutrons
  • (neutral atom) of protons of electrons
  • (charged ion) charge p - e-

22
4.3 How atoms differ
  • Isotopes and Calculations
  • Isotope atoms of the same element with
    different numbers of neutrons
  • Atomic mass weighted average of the masses of
    all the isotopes of an element

23
4.3 How atoms differ
  • Isotope (Isotopic Notation)

Mass
Z
X
Atomic Symbol
A
Atomic
Example Uranium-238
24
4.3 How atoms differ
  • Isotope Problems
  • Multiply the mass number of the isotope by the
    decimal value of the percent for that isotope
  • Add the relative masses of all of the isotopes to
    get the atomic mass of the element

25
4.3 How atoms differ
  • Example
  • If 90 of the Beryllium in the world has a mass
    number of 9 and only 10 has a mass number of 10,
    what is the atomic mass of Beryllium?

26
4.4 Unstable Nuclei and Radioactive Decay
  • Vocabulary
  • Radioactivity-the spontaneous emission of
    radiation from substances
  • Nuclear reactions- changes in an atoms nucleus
  • Radiation-rays and/or particles emitted from
    radioactive material

27
4.4 Unstable Nuclei and Radioactive Decay
  • Types of Radiation
  • Alpha radiation -stream of high energy alpha
    particles
  • alpha particles consist of 2 protons and 2
    neutrons and are identical to helium-4 nucleus.
  • symbol 4He 2
  • 2
  • not much penetrating power, travel a few
    centimeters, stopped by paper, no health hazard

28
4.4 Unstable Nuclei and Radioactive Decay
  • mass number decreases by 4 atomic number by 2
  • alpha decay 226 Ra ? 222Ra 4 He
  • 88 86 2
  • Example Uranium-238

29
4.4 Unstable Nuclei and Radioactive Decay
  • Beta radiation
  • high speed electrons
  • To form beta radiation a neutron splits into a
    proton and an electron
  • The proton stays in nucleus and the electron
    propels out at high speed.
  • Symbol 0e- 0e- 0B
  • -1 -1 -1
  • 100 times more penetrating then alpha, pass
    through clothing to damage skin

30
4.4 Unstable Nuclei and Radioactive Decay
  • Beta decay 131I ? 131 Xe 0B
  • 53 54
    -1
  • Example Astatine-220

31
4.4 Unstable Nuclei and Radioactive Decay
  • Gamma radiation
  • similar to X rays
  • doesnt consist of particles
  • symbol 0?
  • 0
  • penetrates deeply into solid material, body
    tissue, stopped by Pb or concrete, dangerous
  • usually emitted with alpha and beta radiation
  • no mass or electrical charge
  • emission of gamma rays by themselves cannot
    result in the formation of a new atom

32
4.4 Unstable Nuclei and Radioactive Decay
  • Practice
  • What is the alpha decay of plutonium-250?

33
4.4 Unstable Nuclei and Radioactive Decay
  • 2. What is the beta decay of Carbon-14?

34
4.1 Early theories and 4.2 Defining the atom
35
End of Chapter 4!
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