Catalyst – February 20-1, 2013 HW/Vocab Out! Fill in the blanks using the word bank below. Disproven, revise, theory, accept, stronger In science, a _(1)__ is an attempt to explain a particular aspect of the universe. Theories can't be proven, but they can be __(2)__. If observations and tests support a theory, it becomes __(3)__ and usually more scientists will __(4)__it. If the evidence contradicts the theory, scientists must either discard the theory or __(5)__it in light of the new evidence.
Honors HW: Workbook pages 47-49 Today’s Agenda Catalyst Surprise Atomic Theory Day!! Videos, Notes, Thinking, Simulations, etc! Progress Reports and Lab Fees No Exit Question Today HW: Workbook pages 47-48 Honors HW: Workbook pages 47-49
Today’s Objectives SWBAT trace the evolution of atomic theory from 420 B.C. to the present using word descriptions and models. SWBAT identify scientific discoveries that led to new models and more understanding of the atom.
Surprise! Pop Quiz! Must be SILENT! You may use your HOMEWORK AND VOCAB LIST!
Meet your new BEST FRIENDS!!!!
LESSON TITLE: HISTORY AND SCIENCE OF ATOMIC THEORY
Acceptance of Scientific Discovery The Long Version Use the following rules of evidence to examine experimental results: Can an expert's technique or theory be tested, has it been tested, or is it simply a subjective, conclusive approach that cannot be reasonably assessed for reliability? Has the technique or theory been subjected to peer review and publication? What is the known or potential rate of error of the technique or theory when applied? Were standards and controls applied and maintained? Has the technique or theory been generally accepted in the scientific community?
Acceptance of Scientific Discovery “Cliff’s Notes” Use the following rules of evidence to examine experimental results: Has it been adequately tested? Has peer review occurred? What kind of error does it have? Were there standards or control groups? Has it been accepted by scientific community?
What is an atom? Atom: the smallest particle of an element that retains (keeps) its identity in a chemical reaction
Well then, what is an element? NOT THIS KIND OF ELEMENT!!!
Well then, what is an element? NOT THIS KIND OF ELEMENT!!!
Well then, what is an element? Element: the simplest form of matter that has a unique set of properties; an element cannot be broken down into simpler substances by chemical means THESE KINDS OF ELEMENTS
Major Playas of Atomic Theory Democritus (460-370 B.C.) John Dalton (1808) J.J. Thomson (1897) Ernest Rutherford (1909) Niels Bohr (1913) Schrodinger (1926) [James Chadwick (1932)]
Acceptance of Scientific Discovery “Cliff’s Notes” Use the following rules of evidence to examine experimental results: Has it been adequately tested? Has peer review occurred? What kind of error does it have? Were there standards or control groups? Has it been accepted by scientific community?
FIGHTING SCIENTISTS!
VIDEO!
Democritus (460-370 B.C.) Where: Greece When: 420 B.C. Experiment: Observations and inferences No REAL experiment…just IDEAS First “theory” of the atom MODEL
FIGHTING SCIENTISTS!
What were Democritus’ conclusions? Matter is composed of tiny particles called atomos Different kinds of particles have different sizes and shapes Atoms are indivisible and indestructible
And don’t forget! Aristotle challenged the ideas of Democritus by thinking that atoms were NOT divisible….boy was he wrong! Among other things… “We are what we repeatedly do. Excellence, therefore, is not an act but a habit.”
Don’t Forget! The eminent philosophers of the time, Aristotle and Plato, had a more respected, (and ultimately wrong) theory. Aristotle and Plato favored the earth, fire, air and water approach to the nature of matter. Their ideas held sway because of their eminence as philosophers. The atomos idea was buried for approximately 2000 years.
Question to Ponder… Why was Democritus’ idea not a VALID theory?
BACK TO VIDEO!
John Dalton (1766-1844) Where: England When: 1808 Experiment: Many careful chemical measurements and experiments!
Dalton’s Postulates (in textbook) In 1808, John Dalton came up with the first atomic theory that was based on scientific research. It stated: All matter is made of atoms. Atoms are indivisible and indestructible. All atoms of a given element are identical in mass and properties Compounds are formed by a combination of two or more different kinds of atoms. A chemical reaction is a rearrangement of atoms.
What were Dalton’s conclusions? Atoms are hard, round, solid balls. They are similar to marbles. MODEL
WHAT’S IN THE BOX??
Question to Ponder… What makes John Dalton’s ideas about the atom more of a valid theory than the ideas of Democritus?
J. J. Thomson (1856-1940) Where: England When: 1897 Experiment: Cathode ray tube
BACK TO VIDEO!
Thomson Model Where did they come from? This surprised Thomson, because the atoms of the gas were uncharged. Where had the negative charges come from?
Thomson’s Cathode Ray Experiment Passed electric current through gases at low pressure As the current passed through the gas, it was attracted to a positively charged plate outside of the tube
Thomson’s Cathode Ray Experiment -- +
within smaller divisible electrons positively Thomson concluded that the negative charges came from ________ the atom. A particle _________ than an atom had to exist. The atom was _________! within smaller divisible Thomson called the negatively charged “corpuscles,” today known as ____________. Since the gas was known to be neutral, having no charge, he reasoned that there must also be __________ charged particles in the atom. But he could never find them…. electrons positively
What were Thomson’s conclusions? Electrons have a very, very small mass; therefore, they must be smaller than atoms Atoms have parts of them that are negatively charged Credited with discovering the electron
Thomson was pretty hungry when… Now I have finished my model! It looks like Plum Pudding! MODEL
Ernest Rutherford Where: England (University of Manchester) When: 1909 Experiment: Gold Foil Experiment
Ernest Rutherford Where: England (University of Manchester) When: 1909 Experiment: ????
Lil’ Ernie Rutherford on the Scene! Rutherford shot positively charged alpha particles at a very thin piece of gold foil
What Lil’ Ernie thought would happen… If the Plum Pudding model was true, all of the positively charged alpha particles would have gone straight through the foil
What Actually Happened… Almost all of the alpha particles went straight through, but some were deflected 1 in 8000 of the alpha particles was deflected ?
Simulation http://phet.colorado.edu/simulations/sims.php?sim=Rutherford_Scattering
Hint: Positive repels positive, negative repels negative What do you think? Pretend you are Rutherford As Rutherford, what conclusion would you make based on the data from the Gold Foil Experiment? Hint: Positive repels positive, negative repels negative =
Rutherford’s Conclusions The atom is mostly empty space through which negatively charged electrons move There is a tiny, dense region in the center of the atom called the nucleus (positively charged)
- +
MODEL
Relative Size of the Nucleus to the Atom
Still Some Unanswered Questions Rutherford’s model of the atom did not explain HOW the atom’s electrons are arranged in the space around the nucleus Nor did it address the question of WHY the negatively charged electrons are not pulled into the atom’s positively charged nucleus
1900s…Chemical Behavior Scientists observed that certain elements emitted visible light when heated in a flame Analysis of the emitted light revealed that and element’s chemical behavior is related to the arrangement of electrons in atoms
Niels Bohr Where: England (at Rutherford’s lab) When: 1913 Experiment: Atomic emission spectra
The Next Great Idea Niels Bohr studied the atomic emission spectrum for the simplest atom, hydrogen Each orbit has its own fixed energy = energy level With the right amount of energy, electrons can move from one energy level to another, but they cannot exist between energy levels
Atomic Emission Spectra
NOT BOHR-ING AT ALL!!!
Bohr’s Conclusions Electrons orbit around the nucleus in distinct circular paths called ?????!
Bohr’s Conclusions Electrons orbit around the nucleus in distinct circular paths called energy levels!
Erwin Schrodinger Where: Austria When: 1926 Experiment: Furthered other scientists’ work
Wave Model…aka… Quantum Mechanical Model
The Wave Model In fact, it is impossible to determine the exact location of an electron. The probable location of an electron is based on how much energy the electron has. Today’s atomic model is based on the principles of wave mechanics. According to the theory of wave mechanics, electrons do not move about an atom in a definite path, like the planets around the sun.
Schrodinger’s Conclusions If electrons are like waves, then we can predict the location of an electron within a certain space WAVE MODEL aka QUANTUM MECHANICAL MODEL = ATOMIC ORBITALS aka ELECTRON CLOUDS
Schrodinger’s Atomic Orbitals You will learn more about this later!
Right-o! James Chadwick Where: England When: 1932 Experiment: More cathode ray tube Discovered the neutron!
Right-o! James Chadwick Where: England When: 1932 Experiment: More cathode ray tube Discovered the ?????
X Democritus Dalton Thomson Rutherford Bohr Schrodinger Chadwick Indivisible Electron Nucleus Orbits Electron Cloud Neutron Democritus X Dalton Thomson Rutherford Bohr Schrodinger Chadwick