Plum Pudding Model J.J. Thomson 1897 Ernest Rutherford Atomic

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The arrangement of electrons in an atom determine
most of the chemical properties of that atom. Electrons
are what actually do the reacting.
Plum Pudding Model
J.J. Thomson
1897
Ernest Rutherford
Atomic Model
1911
Unanswered Questions:
1) Why do certain gases emit colors of light when electricity is added?
2) Why do metals give off colors when heated?
3) Why do atoms for cations and anions?
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Niels Bohr (1885-1962)
Danish physicist who determined that electrons were actually in distinct
ENERGY LEVELS and not just on the outer edges of the atom.
Electrons could ONLY be found in these circular paths (orbits) around the
nucleus.
Each energy level had a certain amount of energy associated with it. If an
electron contained that "quantum" of energy, then it could maintain that space.
If it couldn't maintain that "quantum" of energy, then it would fall to a lower
energy level.
If it gained energy through some other means, that electron could jump to a
higher energy level.
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Higher Energy
Less Stable
Leaps occur with small
changes in energy
Ground State= the normal
positioning of the electrons
Excited State= electrons have
jumped into higher energy levels
Lower Energy
More Stable
Leaps occur with large
changes in energy
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The fixed energy levels of electrons are somewhat like the
rungs of a ladder.
The lowest rung of the ladder corresponds to the lowest
energy level and most stable positioning.
A person can climb up or down a ladder by going from
rung to rung. Similarly, an electron can jump from one
energy level to another.
A person on a ladder cannot stand between the rungs.
Similarly, the electrons in an atom cannot be between
energy levels.
In general, the higher an electron is on the energy ladder,
the farther it is from the nucleus.
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The Bohr Model explained electron behavior for the
Hydrogen atom (which has one electron).
It failed in many ways to explain the energies absorbed and
emitted by atoms wtih more than one electron.
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1887‐1961
Austrian Physicist
Nobel Prize in 1933
Schrodinger developed a mathematical equation that
would calculate the probability of locating an electron.
These probabilities took the form of different "cloud"
regions.
The Quantum Mechanical Model is based on the principle
that the position of an electron can NEVER be pinpointed in
the same way that a single blade on a spinning propeller
can never be pinpointed.
An electron's position can only be given in terms of a
probable region of space where it can be located.
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What does the Quantum Mechanical Model Tell Us?
Electrons were traveling in cloud‐like
regions rather than in orbits around
the nucleus.
These cloud regions have a unique
shape and size depending upon the
energy level.
Four Quantum Numbers
Numbers are associated with energy
levels, sublevels, orbitals, spins, and
electrons to be used mathematically
in Schrodinger's Equation.
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The Quantum Mechanical Model: What are Quantum Numbers?
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The Quantum Mechanical Model: What are Quantum Numbers?
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The Quantum Mechanical Model: What are Quantum Numbers?
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The Quantum Mechanical Model: What are Quantum Numbers?
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The Quantum Mechanical Model: What are Quantum Numbers?
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Quantum Number Quick Chart
E.L.
n
l
orbitals allowed
m
1
0 (s)
0
# of
orbitals
1
# of
electrons
2
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Quantum Number Notation
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These electron arrangements determine the
chemical properties of every element.
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