Title: Structure of the Atom
1Chapter 4
24.1 Early theories and 4.2 Defining the atom
- Historical Background
- Models of the Atom -see reference chart
- (On Pg. 10 of your packet)
34.1 Early theories and 4.2 Defining the atom
44.1 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
54.1 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
64.1 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
74.1 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
84.1 Early theories and 4.2 Defining the atom
94.1 Early theories and 4.2 Defining the atom
- 4. J.J. Thomson
- cathode ray tube experiments advancement of
Crookes tube - plum-pudding model
104.1 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
114.1 Early theories and 4.2 Defining the atom
Video Clip Rutherford Gold Foil Experiment
124.1 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
134.1 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!
144.1 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
154.1 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
164.1 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
174.3 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.
184.3 How atoms differ
- Subatomic particles the component parts of an
atom proton, neutron, and electron
194.3 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.
204.3 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
214.3 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-
224.3 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
234.3 How atoms differ
- Isotope (Isotopic Notation)
Mass
Z
X
Atomic Symbol
A
Atomic
Example Uranium-238
244.3 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
254.3 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?
264.4 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
274.4 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
284.4 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
294.4 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
304.4 Unstable Nuclei and Radioactive Decay
- Beta decay 131I ? 131 Xe 0B
- 53 54
-1 - Example Astatine-220
314.4 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
324.4 Unstable Nuclei and Radioactive Decay
- Practice
- What is the alpha decay of plutonium-250?
334.4 Unstable Nuclei and Radioactive Decay
- 2. What is the beta decay of Carbon-14?
344.1 Early theories and 4.2 Defining the atom
35End of Chapter 4!