Transcript Notes with questions - Department of Physics and Astronomy

Atoms, Elements and Quantum
Mechanics
01 and 06 October 2015
Physics
Chemistry
Astronomy
Geology/Ecology
Biology
Topics


Discovery of atomic structure and function
Models of atoms
Thompson and Rutherford atom (~1900)
 Bohr atom (1913)
 Quantum mechanics (1930’s)




Elements, atoms and the Periodic Table
Electrons in orbits nested within shells
Valence electrons
Some Notations on the Syllabus

Delete:
Chemical reactions (pp. 223-227)
Chapter 11: Materials and Properties
(pp. 237-259)
Crystal Morphology and Color:
Structure of the Atom
Leaf Color:
Structure of the Atom
Eye Color:
Structure of the Atom
Compounds to Quarks:
A Hierarchy
Compound
Element
Atom
Subatomic Particle
Quarks
(Higgs)
Hierarchy theory and emergent properties
Thompson’s Investigation of the
Electron (1870’s)



Idea: smaller components comprise atoms
Hypothesis: Atoms consist of components,
one of which is negatively charged with a very
small mass
Testing the hypothesis
Thompson’s Experiment
Hypothesis:
Atoms consist of components, one of which is
negatively charged with a very small mass
Methodology
Observations:
1. Deflection of negatively-
charged beam
2. Very small mass
3. Mass same for all elements
Hypothesis: Accept
Particle name: Electron
Rutherford’s Investigation of the
Nucleus (1910)

Idea: other smaller components are part of atoms too,
including ones that are positively charged

Hypothesis: Atoms consist of multiple
subcomponents, one of which is positive in charge

Testing the hypothesis

Alpha particles (+), gold foil, “bullets”, and “tracks”
http://www.youtube.com/watch?v=5pZj0u_XMbc
Observations, Hypothesis,
Conclusion and a Revised Model

Observations




Almost all alpha’s (+) passed through foil unaffected
Very small number of alpha’s (+) deflected at a small angle
1/1,000 bounced back
Hypothesis: Atom consists of a (i) positive component that is
(ii) small in volume in comparison to atom itself

Accept/reject?

Conclusions



Name of particle is the proton
Electrons circling the nucleus
Shortcomings of the new model?
Resolving Shortcoming of the Model:
Atomic Structure and the Bohr Atom

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
emitted (e.g., violet versus
yellow versus red versus
green)

Bohr’s Hypothesis and Model
Quantum Concepts
1.
Only discrete orbits for
electrons
2. Discrete frequency of
photon (emitted
light)
3. Explains spectroscopic
properties of elements
Quantum Behavior and Spectroscopy
Application of Spectroscopy:
Elemental Analysis
Bohr’s Model of the Atom

Building on predecessor models:
Thompson’s electron
 Rutherford’s nucleus and protons



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Electrons in orbits
Orbits exhibit discrete quantum structure/layers
When excited, electrons release energy in
discrete packets of energy (photons of light)
Sequel to Bohr’s atom (2-3 decades): quantum
mechanics
Bohr’s Atom and Spectroscopy
Question
The science of spectroscopy examines the
nature of ___ emitted from excited atoms.
A.
B.
C.
D.
E.
Electrons
Protons
Photons
Neutrons
Galileons
Question
The negatively charged particle that is part of
an atom is the ___.
A.
B.
C.
D.
Photon
Neutron
Proton
Electron
Electrons as Particles and Waves:
Wave-Particle Duality
(Moving Toward Quantum Mechanics)
http://www.youtube.com/watch?v=DfPeprQ7oGc
Theory of Quantum Mechanics

Observations
Quantum behavior of electrons
in Bohr model (orbits, etc.)
 Wave-particle duality of
electrons
Key: integrated mechanisms of
waves and particles, focusing on
“fuzzy electron clouds”



Hypothesis: new evolving model
of atomic structure: quantum
mechanics theory of the atom
 Incorporation of parts of
predecessor
 Plus: wave properties of
electrons in orbits
Question
According to the Rutherford model of the atom,
the volume of any atom is largely _______.
A.
B.
C.
D.
protons and neutrons
electrons
empty space
noxiously sequenced nuons surrounded by
pompous protons
E. none of the above
Question
The existence of a tiny, positively charged atomic nucleus
was deduced from the observation that ___.
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 (very few) alpha particles were deflected by
metal foil
D. all of the above
E. A and C
Question
According to the Bohr model of the atom, an
electron gains or looses energy only by ______.
A.
B.
C.
D.
jumping from one atom to another
speeding up or slowing down in its orbit
jumping from one orbit to another
being removed from the atom
Question
The double-slit experiment was most
important in documenting ___.
A.
B.
C.
D.
The small uncertainty of large objects
The large uncertainty of small objects
The wave-particle duality
The Heisenberg principle
Topics


Discovery of atomic structure and function
Models of atoms
Thompson and Rutherford atoms
 Bohr atom (1913)
 Quantum mechanics (1930’s)




Elements, atoms and the Periodic Table
Electrons in orbits nested within shells
Valence electrons
Elements

Patterns




92 naturally occurring elements (e.g., hydrogen, gold, helium)
Total of 118+
25 of 92 are essential to life (e.g., what are they?)
Key points


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)
Atomic No
Symbol
Name
1
2
H
He
Hydrogen
Helium
6
7
8
C
N
O
Carbon
Nitrogen
Oxygen
17
18
Cl
Ar
Chlorine
Argon
26
53
Fe
I
Iron
Iodine
79
80
Au
Hg
Gold
Mercury
94
104
Pu
Rf
Plutonium
Rutherfordium
Topics


Discovery of atomic structure and function
Models of atoms
Thompson and Rutherford atoms
 Bohr atom (1913)
 Quantum mechanics (1930’s)




Elements, atoms and the Periodic Table
Electrons in orbits nested within shells
Valence electrons
Elements and Compounds

Compound (combinations of atoms)



Elements combine in recurrent, precise and predictable ways
Sodium + Chlorine = Sodium Chloride
Na
+
Cl
=
NaCl
metal
+
gas
=
solid
Key points




Atoms of sodium (Na) and chlorine (Cl) remain atoms of
each respective element
Product (NaCl) is recurrent and predictable
Emergent property: “emergence” of new properties in a
compound not predicted by the summation of the two
elements (hierarchy theory)
Other example: Hydrogen + oxygen = __________
Subatomic Particles


Atoms composed of subatomic particles
Most stable particles




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Neutrons
Protons
Electrons
Other less stable and understood particles (quarks, neutrinos, etc.
… Dr. Geller will speak to this later)
Relationship among the more stable particles
Charge
Mass
Neutron
neutral
2 x 10-24 g
Proton
positive
2 x 10-24 g
Electron
negative
5 x 10-28 g
What is Right About this Model?
What is Not Right About this Model?
Electrons in Orbits
Electrons

Energy “barons” of the atom
(motion and in orbits)
 Energy = ability to do work
 Potential energy = energy
stored due to position or
location (i.e., orbits)

Charge is negative (-) and
particle is “in motion” in a
quantum sense
Key to Electron Structure

Count the number of protons: number of
electrons = number of protons (why?)

Electrons are negative in charge and act as
particles and waves in a quantum sense

Electrons are in motion around the nucleus in
“orbits” that are discrete

Only two electrons exist in a given orbit (Pauli’s
Exclusion Principle)
Electrons

Example of Sulfur (1632S)
(16 electrons in 3 shells)
What are shells, what are orbits and who is Pauli?
Orbits, Shells and Electrons
http://www.colorado.edu/physics/2000/applets/a2.html
Example of Electrons in Shells
As electrons move among shells, they change potential
energy

Hot summer day, bright sun and car top


Light absorption by pigments and electrons “jump” to higher shell
(potential energy); give off energy when they drop back (kinetic/heat
energy)
Banana, orange juice or bagel this AM (how about a granola
bar)?

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/chemical/heat energy)
Some Keys to Electron Structure

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;
special significance in chemistry
Periodic Table of Elements

Concept: most stable state for an atom =
outermost shell filled with maximum number of
electrons

1st Shell (1 orbit; 2 electrons)
Hydrogen (11H; 1 electron; stable ?)
 Helium (24He; 2 electrons; stable ?)


Periodic Table’s 1st Row

Hydrogen and Helium
Orbits, Shells and Electrons
http://www.colorado.edu/physics/2000/applets/a2.html
Atomic Structure: Periodic Table
Unstable
Stable
Periodic Table
Periodic Table of Elements

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)


2nd row of Periodic Table

8 elements
Periodic Table of Elements

Number of elements in a row is not chance;
reflects the maximum number of electrons in
the outermost shell
Row 1 < 2
 Row 2 < 8 (plus Row 1)
 Row 3 < 8 (plus Row 1 + Row 2) )
 Row 4 < 18 (plus Row 1 + Row2 + Row 3)
 Etc.

Periodic Table as a “Model”


Models = conceptual and/or mathematical
expressions that help scientists understand how
the natural world operates
Models foster predictions about how the natural
world operate
Model of the structure of the atom predicts …
 Your model of your family dynamic predicts …


Periodic table predicts that unknown “elements”
have specific physical and chemical properties
Predictive Value of the Periodic Table
??
Question (walk through)
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
Question
In the Periodic Table, carbon is element #6.
This means it has six electrons. How many
valence electrons does carbon have?
A.
B.
C.
D.
E.
1
2
3
4
8
Question
In the Periodic Table, neon is element # 10.
How many electrons does neon have in its
outermost electron shell?
A.
B.
C.
D.
2
4
6
8
Topics


Discovery of atomic structure and function
Models of atoms
Thompson and Rutherford atom (~1900)
 Bohr atom (1913)
 Quantum mechanics (1930’s)




Elements, atoms and the Periodic Table
Electrons in orbits nested within shells
Valence electrons
Atoms, Elements and Quantum
Mechanics
01 and 06 October 2015
Physics
Chemistry
Astronomy
Geology/Ecology
Biology