Download Chemistry Atomic structure Chapter 4, and Chapter 5, p. 146-148

Chemistry
Atomic structure
Chapter 4, and Chapter 5, p. 146-148
Today’s summary
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4.1, 4.2, 4.3,
P. 146-148
Webquest on atomic emission spectra
4.1 history of the atom in thought
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Early ideas about matter
Democritus
John Dalton
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Daltons atomic theory vs Democritus
Dalton = scientific method for experimental
evidence
4.1 conservation of mass
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Mass, matter is not created or destroyed in
ordinary chemical reactions
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Nuclear reactions are a separate topic; NOT
ordinary
4.2
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Defining the Atom
How we discovered the structure of the atom
Who, which experiments
First
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Electrons
In CRTs, cathode ray tubes
Stream of electrons was observed
Sir William Crookes
Mass and charge: J.J. Thompson
Electromagnetic fields
There is a particle smaller than an atom
Mass of electron
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Thompson was able to determine the charge
to mass ratio of the charged particle
Milikan calculated the mass of an electron
Robert Milikan-oil drop experimentdetermined charge of an electron
The plum pudding (blueberry muffin
model)
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Created by JJ Thomson
The model was a circle with electrons in a
disorganized pattern
The model was changed to Rutherford’s
model
The nucleus
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Rutherford
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The Gold Foil Experiment
Protons and neutrons make up the dense
center
Protons have positive charge
Neutrons have negative charge
Incredibly dense
Nucleus, slide 2
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Positively charged nucleus react with positive
alpha particles casing deflections
Electrons around the nucleus are negatively
charged
Completing the model of the atom
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Made of 3 subatomic – electron, proton, and
neutron.
Atoms are shaped with small dense nucleus
of positive charge surrounded by negative
charge
Mostly consisted of fast moving electrons
4.3 how atoms differ
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Atomic number
Henry Moseiev discovered that atoms of
each element contain a unique positive
charge in their nuclei
# of protons in an atom identifies it as an
atom of a particular element.
# of protons= atomic # and # of electrons
Isotopes and mass number
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Isotopes: atoms with the same # of protons
but different #’s of neutrons
Mass of Isotopes: isotopes containing more
neutrons have a greater mass
Isotope Notation: each isotope of an element
is identified with a # called the mass #
Mass # = Atomic # + # of Neutrons
Mass of atoms
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The atomic mass unit is what you measure the mass
of an atom with
The atomic mass is the weighted average mass of
the isotopes.
The atomic mass unit is one twelfth the mass of a
carbon-12 atom.
The standard of atomic mass unit is Carbon-12,
AMU is one-twelfth the mass of carbon atom
Atomic mass depends on the number of protons and
neutrons
Atomic Emission Spectra
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Electromagnetic Radiation- A form of energy exhibiting
wavelike behavior as it travels through space (described by
wave length, frequency, amplitude, and speed)
Electromagnetic Spectrum- Includes all forms of
electromagnetic radiation
Atomic Emission Spectrum- A set of frequencies of
electromagnetic waves given off by atoms of an element,
consists of a series of fine lines of individual colors.
p. 146-148
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When atoms have no added energy they are in their
ground state.
When atoms acquire energy their electrons become
exited and orbit at a further distance from the
nucleus.
Bohr assigned each orbit a different value called a
quantum number.
When the atom returns to its ground state the
electrons revert to their closer orbits which release
light energy that can be observed as the atomic
emission spectrum.