page 23 of your notebook summarize the observed properties of cathode rays that led to the...
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Bellringer (Page 24): What does this represent?
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AtomsPage 23 of your notebook
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Objectives
Summarize the observed properties of cathode rays that led to the discovery of the electron.
Summarize the experiment carried out by Rutherford and his co-workers that led to the discovery of the nucleus.
List the properties of protons, neutrons and electrons.
Define atom and isotope.
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Atoms
Very small 1 x 1022 atoms in 1
penny Equivalent to 1
grain of sand in a sandbox the size of Texas
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Properties of Atoms
Smallest characteristic of a given element
Make up everything Different for each element
Only 90 elements occur in nature
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Atoms
Too small to see with an ordinary microscope
Need scanning tunneling microscope to get an image of an atom Tells nothing about
the structure of an atom
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Atoms
Atoms in Kanji, they spell "atom" using iron atoms on a copper surface. The literal translation is something like "original child."
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Ancient Greeks Theory
Only 4 elements Fire (red) Water (blue) Air (grey) Earth (brown)
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Ancient Greeks and the Atom Democritus
postulated tiny particles of water that could not be subdivided further Called them atomos
(means indivisible)
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Aristotle
Thought everything was continuous
Atoms didn’t exist Ancient Greeks
could not test either model
This view prevailed for >2000 years
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Foundations of Atomic Theory
By the 1790’s, the study of matter was revolutionized by the analysis of chemical reactions Beginning of technology
This lead to the discovery of several basic laws
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Father of Modern Chemistry
law of conservation of matter (mass):
The total mass of substances does not change during a chemical reaction.
reactant 1 + reactant 2
total mass
product
total mass=
iron + oxygen iron(III) oxide
Fe + O2 Fe2O3
70.0 g + 30.0 g 100.0 g
100.0 g
Antoine Lavoisier (1743-1794)
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Lavoisier Accurately weighed starting
materials and products of reactions
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Law of Conservation of Mass
Mass is neither created nor destroyed during chemical reactions
Cannot create material out of thin air Make new materials by rearranging
atoms Basis for chemical calculations
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1. All matter is composed of extremely small particles
Atoms are indivisible2. Atoms of a given element
are alike but different from atoms of any other element
Atoms for any element have identical chemical and physical properties
1803 John Dalton:
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3. Atoms can not be subdivided, created or destroyed.
4. Compounds are formed when different elements combine in fixed proportions
▪ Typically written with smallest whole numbers - Law of Definite Proportions - Law of Multiple Proportions
1803 John Dalton:
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5. A chemical reaction involves combining, separating or rearranging of atoms
• Law of Conservation of Mass
1803 John Dalton:
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Modern Atomic Theory
Modern Atomic Theory proved a few of Daltons ideas where wrong. Atoms are divisible into smaller particles▪ Electrons, neutrons and protons
A given element can have atoms with different masses▪ Isotopes
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The Discovery of Atomic Structure
Cathode rays – The ray of light emitted by the cathode (negative electrode) in a glass discharge tube; travels in straight lines, unless deflected by magnetic or electric fields.
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Studied cathode rays and determined that
J. J. Thomson (1897)
Atoms are divisible into even smaller
particles.
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Millikan’s Oil-Drop Experiment
Determined the negative charge of an electron
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James Chadwick
• Discovered a particle in the nucleus that had no charge•neutron
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Roentgen
Studied the glow caused by the cathode ray tube
Chemically treated paper that glowed▪ Even through
walls!
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Discovery of RadioactivityBecquerel
found that uranium ores would fog photographic plates in the dark
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Marie and Pierre Curie Marie and Pierre
Curie isolated 1/30 ounce ofradium from one ton ofuranium ore.
Marie died fromradiation-inducedleukemia.
The pages of her labnotebook were laterfound to becontaminated withradioactivefingerprints.
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Radioactivity
– spontaneous emission of radiation from certain unstable elements
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Behavior of Radioactivity
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Rutherford’s Experiment
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The Discovery of Atomic Structure
Rutherford’s a-Scattering Experiment (Gold Foil) and Discovery of the Atomic Nucleus
The vast majority of an atom’s volume is empty space.
Nucleus - The tiny central region of the atom that contains the positive charge and essentially all the mass.
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Structure of Atom
Rutherford suggested: Most of mass in nucleus All the positive charge
Nucleus: protons and neutrons Neutrons have mass but
no charge Very small size compared
to the rest of the atom The rest of the atom
contains the electrons
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Subatomic Particles
Particles smaller than the atom Number of protons in element = atomic
number Element: all atoms having the same
atomic number
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Atomic Structure
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Isotopes Atoms having the same atomic
number BUT differing in number of
neutrons
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Symbols for Isotopes
ZAX
A = mass number = number of protons + number of neutrons = number of nucleonsZ = atomic numberX – symbol of the element
Isotopes of hydrogen
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A Neutron walked into a bar and asked how much for a drink. The bartender replied, “for you…. no charge.”
-Jaime- Internet Chemistry Jokes
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