Download Atomic Structure and Function - Department of Physics and Astronomy

Atoms and Periodic Properties
Topics
Honors 227
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Physics
Discovery of atomic structure and function
Models of atoms
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Chemistry
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Astronomy
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Geology
Biology
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Scientific Method
Elements and atoms
Electrons and orbits/shells
Valence electrons
Models in the Sciences
Example: Dynamics of family
interactions
Observations
Reject/Accept
Bohr atom (1913)
Quantum mechanics (1930’s)
Hypothesis
Test of Hypothesis
Example for atoms:
1. Atom as a marble
2. Atom as the solar system
3. Atom with protons,
neutrons and electrons
Models: abstraction and meant
to be challenged
Protons and
Neutron
Crystal Morphology and Color:
Atomic Structure
Electrons in
orbits
Leaf Color and Atomic Structure
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Compounds to Subatomic Particles:
A Hierarchy
Compound
Emergent Properties?
Thompson’s Investigation of the
Electron
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Element
Atom
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Idea that smaller components comprise atoms
Hypothesis: Atoms consist of subcomponents,
one of which is negatively charged with a very
small mass
Testing the hypothesis
Subatomic Particles
Rutherford’s Investigation of the
Nucleus
Thompson’s Experiment
Methodology
Observations:
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1. Deflection of negatively-
charged beam
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2. Very small mass relative to
charge
3. Mass same for all elements
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Idea that other smaller components are part of
atoms, including ones that are positively charged
Hypothesis: Atoms consist of multiple
subcomponents, some of which are positive
Testing the hypothesis
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tested
Alpha particles (+), gold foil, “bullets”, and “tracks”
Hypothesis: Accept
Particle name: Electron
Rutherford’s Experiment:
Methodology
Observations, Hypothesis and
Conclusion
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Observations
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Almost all alpha’s (+) passed through foil unaffected
Very small number of alpha’s (+) deflected at a small angle
1/1000 bounced back
Hypothesis: Atom consists of a positive
subcomponent that is small in volume in comparison
to atom itself
Accept/reject?
Conclusions:
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radius of nucleus is 10-4 x radius of atom
Name of particle is the proton
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Hypothesis and Model
Atomic Structure: Bohr Atom
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Observations (1913)
Heat hydrogen gas and light emitted as a discrete
wavelengths (not continuous spectrum)
„ Other gases behave the same in producing discrete
wavelength, but each gas is unique in wavelengths
emitted (e.g., violet versus yellow versus red)
Quantum Concepts:
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1. Only allowed orbits for
electrons
2. Discrete frequency of
photon (emitted light)
Theory of Quantum Mechanics
Model: Quantum Mechanics
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Observations
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Investigators (Heisenberg, Shrodinger): wave-particle
duality of light (remember Dr. Geller’s lecture)
Key: integrated mechanisms of waves and particles,
focusing on “fuzzy electron clouds”/waves
Hypothesis: new model of atomic structure and
function: quantum mechanics theory of the atom
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Questions
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Is a model in the sciences a form of an
hypothesis?
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A
B
Yes
No
All of these models (when accepted or rejected)
resulted in scientific revolutions in physics. Are
revolutions in the sciences somewhat analogous
to revolutions in society?
Behavior of electrons in heated hydrogen gas consistent with
Bohr Model (orbits, etc.)
Behavior of other heavier gases not explained by Bohr Model
Incorporation of known facts (Bohr model as particles)
Wave properties of electrons in orbits
Prediction of new properties yet to be discovered
Question
According to the Rutherford model of the atom,
the volume of any atom is largely _______.
A. protons and neutrons
B. electrons
C. empty space
D. noxiously sequenced nuons surrounded by
pompous protons
E. none of the above
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Question
Question
According to the Bohr model of the atom, an
electron gains or looses energy only by ______.
The existence of a tiny, massive, and positively charged
atomic nucleus was deduced from the observation that
___.
A. jumping from one atom to another
B. speeding up or slowing down in its
orbit
C. jumping from one orbit to another
D. being removed from the atom
A. fast, massive, and positively charged alpha particles
move in straight lines through gold foil
B. alpha particles were deflected by a magnetic field
C. some alpha particles were deflected by metal foil
D. all of the above
Elements
Topics
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Discovery of atom structure and function
Models of atoms
Bohr atom (1913)
„ Quantum mechanics (1930’s)
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Symbol
Name
1
2
H
He
Hydrogen
Helium
6
7
8
C
N
O
Carbon
Nitrogen
Oxygen
17
18
Cl
Ar
Chlorine
Argon
26
27
Fe
Co
Iron
Cobalt
53
I
Iodine
73
74
Ta
W
Tantalum
Tungsten
79
80
Au
Hg
Gold
Mercury
94
Pu
Plutonium
104
Rf
Rutherfordium
92 naturally occurring elements (e.g., hydrogen, gold, helium)
Total of 113
25 of 92 are essential to life (e.g., what are they?)
Key points
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Elements and atoms
Electrons and orbits nested within shells
Valence electrons
At No
Patterns
„
any element is the same in its chemical structure and physical
properties (stable over time, with one exception - radioactive
elements)
All elements have origin in either the big bang (hydrogen and
helium) or the subsequent evolution of the universe (Dr.
Geller will speak to this a bit later)
Elements and Compounds
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Compound
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Elements combine in very precise ways that are recurrent and
predictable
Sodium + Chlorine = Sodium Chloride
Na
+
Cl
=
NaCl
metal
+
gas
=
solid
Key points
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Atoms of sodium (Na) and chlorine (Cl) remain atoms of
each
Product (NaCl) is recurrent and predictable
Emergent property: “emergence” of new properties in a
compound not be explained by the summation of the two
elements (hierarchy theory)
Other example: Hydrogen + oxygen = __________
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Compounds to Subatomic Particles:
A Hierarchy
Subatomic Particles
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Compound
Emergent Properties
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Atoms are composed of subatomic particles
Most stable particles
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Element
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Neutrons
Protons
Electrons
Other less stable particles (quarks, neutrinos, etc.)
Relationship among the more stable particles
Atom
Subatomic Particle
Old Model of Atom and its Particles
Charge
Mass
Atoms of the same element have the same number of
subatomic particles, abbreviated as follows:
2
Helium
Electrons
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Abbreviation of element
Atomic mass (g/mole)
1
Hydrogen
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# of protons
He
4
H
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1
Mass =
Electron
negative
5x10-28 g
Modern Model of Atom and Particles
Atomic Structure
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Proton
positive
2x10-24 g
Electrons in
orbits
Protons and
Neutron
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Neutron
neutral
2x10-24 g
Protons + Neutrons
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Background of quantum mechanics
Energy “barons” of the atom (motion)
„ Energy = ability to do work
„ Potential energy = energy stored due to
position or location (analogy to water in a
tower)
Charge is negative (-) and particle is always in
motion
Capturing an atom and its orbiting electron may
be difficult (why?)
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Electrons
Key to Electron Structure
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Count the number of protons as the number of
electrons = number of protons
Electrons are negative in charge and in
constant motion (as a wave)
Electrons are in orbits around the nucleus and
orbits are nested within shells
Example of Sulfur (1632S)
(16 electrons in 3 shells)
What are shells and what are orbits?
Example of Electrons in Shells
Quantum Mechanics and Orbits
As electrons move among shells, they change
potential energy
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Hot summer day, bright sun and car top
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Banana, orange juice or bagel this AM?
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Some Keys to Electron Structure
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Electrons reside in shells as a function of
quantum mechanics (1-4 orbits per shell)
Never more than two electrons per orbit (Pauli’s
Exclusion Principle)
Distribution of electrons is key to understanding
why elements and atoms behave the way they do
Outermost electrons are called valence electrons;
they have special significance in chemistry
Light absorption by pigments and electrons “jump” to
higher shell (potential energy); give off energy when they
drop back (kinetic energy)
Excited electron “captured” by chlorophyll in leaf and
shuttled to a sugar molecule in its excited state (potential
energy) until you release the energy via digestion, allowing
the electron to “drop back” to a lower orbit (kinetic energy)
Periodic Table of Elements
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Concept: most stable state for an atom is one in
which the outermost shell is filled with the
maximum number of electrons
1st Shell (1 orbit; 2 electrons)
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Hydrogen (11H; 1 electron; stable ?)
Helium (24He; 2 electrons; stable ?)
Periodic Table’s 1st Row
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Hydrogen and Helium
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Periodic Table of Elements
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2nd shell has 4 orbits with 2 electrons
(maximum) per orbit (total of 8 electrons/shell)
Most stable configuration is:
1st shell filled with 2 electrons
2nd shell filled with 8 electrons
„ Total of 10 electrons (1020Ne)
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2nd row of Periodic Table
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8 elements
Periodic Table of Elements
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3nd shell has 4 orbits with 2 electrons maximum
per orbit (total of 8 electrons/shell)
Most stable configuration is the following:
1st shell filled with 2 electrons
2nd shell filled with 8 electrons
„ 3rd shell filled with 8 electrons
„ Total of ___ electrons (1840Ar)
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3nd row of Periodic Table
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8 elements (list and relate to the above)
Periodic Table of Elements
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Predictive Value of Periodic Table
Number of elements in a row is not chance but
reflects the maximum number of electrons in
the outermost shell
Row 1 = 2
Row 2 = 8
„ Row 3 = 8
„ Row 4 = 18
„ etc
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Discussion Question
As you scan the night sky, you see multiple objects and
question whether these objects are similar to or
different from the Earth in chemical composition (i.e.,
elements).
Suppose the person next to you says that she has an
instrument that can identify the occurrence of specific
atoms (e.g., sodium, hydrogen, sulfur) based on the
energy patterns/signatures of electrons in atoms on
that planet. Could she be right?
A
Yes
B
No
Question
In the list below, an atom of _______ has the
greatest ability to attract electrons.
A. silicon
B. sulfur
C. krypton
D. chlorine
E. sodium
Question
In the list below, an atom of _______ has the least
ability to attract electrons.
A. silicon
B. sulfur
C. krypton
D. chlorine
E. sodium
Discussion Question
Discussion Question
Models are one of the key investigative tools in
the scientific arsenal. Models of our
understanding of the atom are a classic example
of the role that models play in the sciences.
In many ways, the Periodic Table is a “model”
to help scientists understand patterns in the
natural world. List ways in which this model
helps scientists to understand the natural world?
List four features of models – not the specifics
of any given model, but rather how models are
constructed, how they promote our
understanding of natural systems, and how their
fallibility is an asset.
How does this model compare with that of
Rutherford’s model or the quantum mechanics
model of the atom?
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