Transcript Atomic Structure and Function

Atomic Structure and Function:
Outline
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Early history in 18th and 19th centuries
Discovery of elements and the Periodic Table (1869)
Discovery of the electron (1897)
Discovery of the nucleus (1911)
Atomic structure with consternation
Atomic structure: the Bohr atom (1913)
Atomic Structure: Theory of Quantum Mechanics
(1930’s)
• Applications of our understanding
Atomic Structure and Function:
Take Home Message
• Science as a evolutionary, incremental process
over decades (e.g., exploring the structure of
atom)
• Role of hypothesis development and testing in
the sciences
• Demystification of physics and chemistry:
structure of the atom is a simple concept
• Understanding of atomic structure underpins
future course topics (e.g., geology, biochemistry,
environmental sciences, binding of chemicals)
• Applications – some examples
Early History in 18th and 19th
Century
• Atomic Theory of Dalton
– Atoms
– Elements
– Molecules/compounds (e.g., water or H2O)
• Atoms as basis for understanding
chemistry but without electrons, protons
and neutrons (analogy to a marble)
Early History in 18th/19th Century:
Discovery of Elements
• 30 elements known in early 1800’s
• Mendeleev and the Periodic Table (1869)
– 63 elements known w/o any organization
– Ordering of elements
• Mass from low to high
• Chemical property by column (all behave similarly in a
chemical sense); examples
– Column I: react with chlorine (1:1 ratio)
» Hydrogen (H), Lithium (Li), Sodium (Na), Potassium (K)
– Column VII: react with chlorine in (2:1 ratio)
» Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr)
Draft of Mendeleev’s Table of
Elements
Mendeleev’s Contribution
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Arrange elements from light to heavy
Arranged elements by chemical behavior
Spatial ordering via rows and columns
Product: Periodic Table of Elements
– Predictive tool
– Immensely creative insight (informatics)
– Example of missing elements and predictive
capability of Table
Atomic Structure and Function:
Outline
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Early history in 18th and 19th centuries
Discovery of the electron (1897)
Discovery of the nucleus (1911)
Atomic structure with consternation
Atomic structure: the Bohr atom (1913)
Atomic Structure: Theory of Quantum
Mechanics (1930’s)
• Applications of our understanding
Thompson’s Experiment: Discovery
of the Electron
• Idea that there may be some smaller
components that comprise atoms
• Hypothesis: Atoms consist of some
subcomponents, one of which is
negatively charged
• Experiment to test hypothesis
Atomic Structure and Function:
Outline
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Early history in 18th and 19th centuries
Discovery of the electron (1897)
Discovery of the nucleus (1911)
Atomic structure with consternation
Atomic structure: the Bohr atom (1913)
Atomic Structure: Theory of Quantum
Mechanics (1930’s)
• Applications of our understanding
Rutherford’s Experiment: Discovery
of a Nucleus
• Idea that there may be some smaller
components that comprise atoms, including
negative and positive charges components
• Hypothesis: Atoms consist of multiple
subcomponents, some negative and some
positive
• Experiment to test hypothesis
– Alpha particles (+), gold foil, “bullets”, and “tracks”
Rutherford’s Experiment:
Explanation
Observations, Hypothesis and
Conclusion
• Observations:
– Almost all alpha’s passed through foil unaffected
– Very small number of alpha’s deflected @ small
angle
– 1/1000 deflected at large angle (struck “head on”)
• Hypothesis: Atoms consist of some positive
and negative subcomponents
• Accept or reject
New Model of Atom
• Small, dense center, positively charged –
called the nucleus (later to be called the
proton)
• Small, light (w/o mass) negative charged
subcomponent circles the nucleus (electron)
• Later additions (1932)
– Neutrons
– Protons
– Charge (neutrality calls for + and – charges)
Atomic Structure and Function:
Outline
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•
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Early history in 18th and 19th centuries
Discovery of the electron (1897)
Discovery of the nucleus (1911)
Atomic structure with consternation
Atomic structure: the Bohr atom (1913)
Atomic Structure: Theory of Quantum
Mechanics (1930’s)
• Applications of our understanding
Atomic Structure with
Consternation
Logic of consternation with Rutherford
Model
– Electrons moving, so must give off energy;
– 2nd Law of Thermodynamics
– Electrons should collapse
– Yet atoms are billions of years old
Conclusions: Model violated
fundamental laws of physics
Atomic Structure and Function:
Outline
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Early history in 18th and 19th centuries
Discovery of the electron (1897)
Discovery of the nucleus (1911)
Atomic structure with consternation
Atomic structure: the Bohr atom (1913)
Atomic Structure: Theory of Quantum
Mechanics (1930’s)
• Applications of our understanding
Atomic Structure: Bohr Atom
• Observations (1913)
– Heated hydrogen gas and light is emitted as
a discrete wavelength (not continuous
spectrum)
– Other gases behave the same in producing
discrete wavelength, but each gas unique in
wavelengths produced
Atomic Structure: Bohr Atom
• Hypothesis
– Electrons circle the nucleus at specific
distances from the nucleus in defined orbits
• Diagram
Atomic Structure: Bohr Atom
• Explanation of light in discrete
wavelengths
– As “excited”/heated electrons drop back from
orbit, a packet of energy is lost as a function
of distance from the nucleus
– Packet of energy is called photon (light)
Atomic Structure: Bohr Atom
• Key aspects of the Bohr atom
– No space between the orbits for electrons to be so
“jump” has to be “all or none” – quantum levels of
electrons
– Excited electrons in outer orbit has 2 options:
• Drop down to next lower orbit and emit a packet of energy
(light) unique for that distance
• Drop back to even lower level (ground state) and emit
packet of energy (light) unique for that that distance
– Energy release is unique for each element and is a
“window” on atomic structure”
• Ideas verified two decades later using quantum
mechanics
Atomic Structure and Function:
Outline
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Early history in 18th and 19th centuries
Discovery of the electron (1897)
Discovery of the nucleus (1911)
Atomic structure with consternation
Atomic structure: the Bohr atom (1913)
Atomic Structure: Theory of Quantum
Mechanics (1930’s)
• Applications of our understanding
Theory of Quantum Mechanics
• Observations
– Behavior of electrons in heated hydrogen gas were
consistent with Bohr Model (orbits, etc.)
– Behavior of other heavier gases could not be
explained by Bohr Model
• Investigators:
– Heisenberg, Shrodinger, etc.
• Key: Integrated mechanisms of waves and
particles, focusing on “fuzzy electron clouds”
• Product: new model of atomic structure and
function
– “Quantum mechanics”
Quantum Mechanics Model
• Key Principles
– Electron behaves as a wave not a particle
– Energy of electron behaves as a “spread-out
wave” – not discrete bundle of energy
• Description is based on quantum numbers
– Distance from nucleus
– Energy level and sublevel
– Orientation of electrons in space
– Direction of electron spin
Quantum Mechanics Model:
Principle Energy Level
• Main energy level of electrons
• Distance from nucleus
– n = 1 (lowest energy level)
–n=2
–n=3
– n = 4 (highest energy level)
– etc.
Quantum Mechanics Model:
Sub-energy Levels
• Electrons in “fuzzy” probability distribution
called an “orbital”
– e.g., n = 1 has I sub-energy level/orbital (2
electron orientations)
• Electrons in an orbital can only exist in
pairs (2) and the pair spin in opposite
directions
– Pauli Exclusion Principle
Quantum Mechanics Model:
Electron Configuration
• Electrons always adopt most energetically stable
energy levels/orbitals consistent with Laws of
Thermodynamics and previous conditions
(above)
– n = 1 with 2 electrons in 1 orbital (s orbital)
– n = 2 with 8 electrons in 4 orbitals (p orbitals)
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pw has 2 electrons
px has 2 electrons
py has 2 electrons
pz has 2 electrons
Atomic Structure and Function:
Outline
•
•
•
•
•
•
Early history in 18th and 19th centuries
Discovery of the electron (1897)
Discovery of the nucleus (1911)
Atomic structure with consternation
Atomic structure: the Bohr atom (1913)
Atomic Structure: Theory of Quantum
Mechanics (1930’s)
• Applications of our understanding
Applications of Our Understanding
of Atomic Structure
• Spectroscopy: quantum differences in light
emitted or absorbed result in unique signature for
each element (“fingerprint”)
• LASER (Light Amplification by Stimulated
Emission of Radiation)
• Binding of elements to create compounds
• Neurotransmitters in the brain
• Allergy reactions
• Etc……………..
Atomic Structure and Function:
Take Home Message
• Science as a evolutionary, incremental process
over decades (e.g., exploring the structure of
atom)
• Role of hypothesis development and testing in
the sciences
• Demystification of physics and chemistry:
structure of the atom is a simple concept
• Understanding of atomic structure underpins
future course topics (e.g., geology, biochemistry,
environmental sciences, binding of chemicals)
• Applications – some examples