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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.

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Presentation on theme: "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."— Presentation transcript:

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  1. Atomists and Democritus Greeks approx 2,500 years ago Matter was made up of atoms  “atomos” or “Indivisible” particles Seashell experiment—broken into smaller & smaller pieces

5 4.1 Early theories and 4.2 Defining the atom  2. John Dalton ; 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 1870’s first evidence for existence of electrons because you could “see” electrons flow and confirm their existence. tube is precursor to today’s 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 = nm  Atom diameter = nm  Nucleus = basketball --> Atom = 6 miles wide!

14 4.1 Early theories and 4.2 Defining the atom  8. Niels Bohr improved on Rutherford’s 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!  atom atom 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 AbbreviationChargeLocationDiscoverer Proton1 amu, p + +1NucleusNone Neutron1 amu, n0NucleusChadwick in 1932 ElectronAlmost zero, e - 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 # Atomic # Atomic Symbol Z A X 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 atom’s 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 4 He 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  222 Ra + 4 He  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 0 e- 0 e- 0 B  100 times more penetrating then alpha, pass through clothing to damage skin

30 4.4 Unstable Nuclei and Radioactive Decay  Beta decay: 131 I  131 Xe + 0 B  Example: Astatine-220

31 4.4 Unstable Nuclei and Radioactive Decay  Gamma radiation similar to X rays doesn’t 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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