1. Atoms and Elements 30 September 2004 Physics Chemistry Chemistry Astronomy Astronomy Geology Geology Biology Biology

2. Topics Discovery of what an atom is composed Discovery of what an atom is composed Models of atoms Models of atoms Bohr atom (1913) Bohr atom (1913) Quantum mechanics (1930’s) Quantum mechanics (1930’s) Elements and atoms Elements and atoms Electrons and shells/orbits Electrons and shells/orbits Valence electrons Valence electrons

3. Synopsis (1 st lecture) Principles of physics, astronomy, chemistry, geology, and biology Principles of physics, astronomy, chemistry, geology, and biology Dominant theories and laws that underlie how the natural world operates Dominant theories and laws that underlie how the natural world operates Theories and laws are relevant in every day life Theories and laws are relevant in every day life Underlying themes across all disciplines (e.g., emergent properties, models, scientific method) Underlying themes across all disciplines (e.g., emergent properties, models, scientific method) Cardinal features of scientific investigations (e.g., scientific method, data visualization, models, data collection), through a combination of computer simulations and hands-on experiments in lab Cardinal features of scientific investigations (e.g., scientific method, data visualization, models, data collection), through a combination of computer simulations and hands-on experiments in lab

4. Models in the Sciences Conceptual models based on observations Conceptual models based on observations Example:Dynamics of family interactions Example:Dynamics of family interactions Example:Structure of the atom (protons, neutrons and electrons Example:Structure of the atom (protons, neutrons and electrons Models are an abstraction and are meant to be challenged Models are an abstraction and are meant to be challenged Protons and Neutron Electrons in orbits

5. Scientific Method Observations Proposal/Hypothesis Testing Hypothesis Rejection/Acceptance of Hypothesis

6. Crystals: Structure and Color

7. Topics Discovery of what an atom is composed Discovery of what an atom is composed Models of atoms Models of atoms Bohr atom (1913) Bohr atom (1913) Quantum mechanics (1930’s) Quantum mechanics (1930’s) Elements and atoms Elements and atoms Electrons and shells/orbits Electrons and shells/orbits Valence electrons Valence electrons

8. Compounds to Subatomic Particles: A Hierarchy Compound Element ElementAtom Subatomic Particle Subatomic Particle

9. Thompson’s Discovery of the Electron Idea that there may be some smaller components that comprise atoms Idea that there may be some smaller components that comprise atoms Hypothesis: Atoms consist of subcomponents, one of which is negatively charged and very small in mass Hypothesis: Atoms consist of subcomponents, one of which is negatively charged and very small in mass Experiment to test hypothesis Experiment to test hypothesis

10. Thompson’s Experiment

11. Rutherford’s Discovery of a Nucleus Idea that there may be some smaller components that comprise atoms, including negatively and positively charges components Idea that there may be some smaller components that comprise atoms, including negatively and positively charges components Hypothesis: Atoms consist of multiple subcomponents, some negative and some positive Hypothesis: Atoms consist of multiple subcomponents, some negative and some positive Experiment to test hypothesis Experiment to test hypothesis Alpha particles (+), gold foil, “bullets”, and “tracks” Alpha particles (+), gold foil, “bullets”, and “tracks”

12. Rutherford’s Experiment:

13. Observations, Hypothesis and Conclusion Observations Observations Almost all alpha’s passed through foil unaffected Almost all alpha’s passed through foil unaffected Very small number of alpha’s deflected @ small angle Very small number of alpha’s deflected @ small angle 1/1000 deflected at large angle (struck “head on”) 1/1000 deflected at large angle (struck “head on”) Hypothesis: Atom consists of a positive subcomponent that is very small in volume in comparison to atom itself Hypothesis: Atom consists of a positive subcomponent that is very small in volume in comparison to atom itself Accept the hypothesis Accept the hypothesis

14. Atomic Structure: Bohr Atom Observations (1913) Observations (1913) Heat hydrogen gas and light is emitted as a discrete wavelength (not continuous spectrum) Heat 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 is unique in wavelengths emitted Other gases behave the same in producing discrete wavelength, but each gas is unique in wavelengths emitted

15. Bohr Atom

16. A Model of Quantum Mechanics

17. Theory of Quantum Mechanics Observations Observations Behavior of electrons in heated hydrogen gas consistent with Bohr Model (orbits, etc.) Behavior of electrons in heated hydrogen gas consistent with Bohr Model (orbits, etc.) Behavior of other heavier gases not explained by Bohr Model Behavior of other heavier gases not explained by Bohr Model Investigators (Heisenberg, Shrodinger): wave-particle duality of light Investigators (Heisenberg, Shrodinger): wave-particle duality of light Key: integrated mechanisms of waves and particles, focusing on “fuzzy electron clouds”/waves 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 Hypothesis: new model of atomic structure and function: quantum mechanics theory of the atom Incorporation of know facts Incorporation of know facts Prediction of new properties yet to be discovered Prediction of new properties yet to be discovered

18. Models in the Sciences Conceptual models based on observations Conceptual models based on observations Example:Dynamics of family interactions Example:Dynamics of family interactions Example:Structure of the atom (protons, neutrons and electrons Example:Structure of the atom (protons, neutrons and electrons Models are an abstraction and are meant to be challenged Models are an abstraction and are meant to be challenged Protons and Neutron Electrons in orbits

19. Elements Patterns Patterns 92 naturally occurring elements (e.g., hydrogen, gold, helium) 92 naturally occurring elements (e.g., hydrogen, gold, helium) Total of 113 Total of 113 25 of 92 are essential to life (e.g., what are they?) 25 of 92 are essential to life (e.g., what are they?) Key points Key points any element is the same in its chemical structure and physical properties (~stable over time) any element is the same in its chemical structure and physical properties (~stable over time) All elements have origin in either the big bang (hydrogen and helium) or the subsequent evolution of the universe All elements have origin in either the big bang (hydrogen and helium) or the subsequent evolution of the universe

20. Elements Compound Compound Elements combine in very precise ways that are recurrent and predictable Elements combine in very precise ways that are recurrent and predictable Sodium + Chlorine = Sodium Chloride Na+ Cl = NaCl Na+ Cl = NaCl metal + gas = solid Key points Key points Atoms of sodium (Na) and chlorine (Cl) remain atoms of each Atoms of sodium (Na) and chlorine (Cl) remain atoms of each Emergent property: “emergence” of new properties in a compound not be explained by the summation of the two elements (hierarchy theory) Emergent property: “emergence” of new properties in a compound not be explained by the summation of the two elements (hierarchy theory)

21. Particles Atoms are composed of particles (subatomic particles) Atoms are composed of particles (subatomic particles) Most stable particles Most stable particles Neutrons Neutrons Protons Protons Electrons Electrons Other less stable particles (quarks, neutrinos, etc.) Other less stable particles (quarks, neutrinos, etc.) Relationship among the more stable particles Relationship among the more stable particles Neutron ProtonElectron Chargeneutralpositivenegative Mass 2x10 -24 g 2x10 -24 g 5x10 -28 g

22. Atomic Structure Atoms of the same element (e.g., hydrogen, helium, gold) have the same number of subatomic particles and by convention we abbreviate as follows: Atoms of the same element (e.g., hydrogen, helium, gold) have the same number of subatomic particles and by convention we abbreviate as follows: 2# of protons 2# of protons HeliumHeAbbreviation of element 4Atomic mass (g/mole) 4Atomic mass (g/mole) 1 HydrogenH 1 Mass = Protons + Neutrons Mass = Protons + Neutrons

23. Electrons Background of quantum mechanics Background of quantum mechanics Energy “barons” of the atom (motion) Energy “barons” of the atom (motion) Energy = ability to do work Energy = ability to do work Potential energy = energy stored due to position or location Potential energy = energy stored due to position or location Charge is negative (-) and particle is always in motion Charge is negative (-) and particle is always in motion Capturing an atom and its orbiting electron Capturing an atom and its orbiting electron

24. Key to Electron Structure Count the number of electrons (and compare with abbreviation of element) Count the number of electrons (and compare with abbreviation of element) Electrons are negative in charge and in constant motion Electrons are negative in charge and in constant motion Electrons are in orbits around the nucleus Electrons are in orbits around the nucleus Chemists sometimes refer to orbits as “shells” Chemists sometimes refer to orbits as “shells”

25. Electrons Example of Sulfur ( 16 32 S) Example of Sulfur ( 16 32 S) (16 electrons in 3 orbits)

26. Example of Electrons in Shells As electrons move between shells, they change potential energy As electrons move between shells, they change potential energy Hot summer day, bright sun and car top 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 energy) Light absorption by pigments and electrons “jump” to higher shell (potential energy); give off energy when they drop back (kinetic energy) Banana, orange juice or bagel this AM? Banana, orange juice or bagel this AM? 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/respiration, allowing the electron to “drop back” to a lower level (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/respiration, allowing the electron to “drop back” to a lower level (kinetic energy)

27. Some keys to Electron Structure Electrons reside in shells as a function of quantum mechanics (1-4 orbits per shell) 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) 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 Distribution of electrons is key to understanding why elements and atoms behave the way they do Outermost electrons are called valence electrons and they have a very special significance in chemistry Outermost electrons are called valence electrons and they have a very special significance in chemistry

28. 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.covertly sequenced nuons surrounded by proton Question

29. According to the Bohr model of the atom, an electron gains or looses energy only by ______. 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 Question

30. 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.covertly sequenced nuons surrounded by proton Question

31. 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.covertly sequenced nuons surrounded by proton Question

32. Discussion Question As you scan the night sky, you see multiple objects, and you question whether these objects are similar to or different from Earth. 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 (PE and KE) in atoms on that planet. Could she be right?

33. Discussion Question Models are one of the key investigative tools in the scientific method. Models of our understanding of the atom are a classic example of the role that models play in the sciences. List five features of models – not the specifics of any given model, but rather how models are constructed, how they serve to help promote our understanding of natural systems, and their fallibility.

34. Discussion Question You are in the atomic world, having won a free all day ride on an electron nested within a carbon atom. Your peers are jealous (hang with me on this). You are seated on an electron, duly belted down with a safety harness and off you go. Twenty-four hours later you return to life at GMU. List the cardinal features of your “ride”.