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Atomic Theory What is it? What is it? Who figured it out? Who figured it out? When did they do it? When did they do it? How did they do it? How did they.

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Presentation on theme: "Atomic Theory What is it? What is it? Who figured it out? Who figured it out? When did they do it? When did they do it? How did they do it? How did they."— Presentation transcript:

1 Atomic Theory What is it? What is it? Who figured it out? Who figured it out? When did they do it? When did they do it? How did they do it? How did they do it? Why do we believe it? Why do we believe it?

2 What can you tell from this picture?

3 What is an ATOM? An atom is the smallest particle of an element that retains the identity of the element. An atom is the smallest particle of an element that retains the identity of the element. 

4 ATOM

5 Atoms combine to form compounds

6 The Ancient Greeks Democritus Democritus Lived 450 B.C. Lived 450 B.C. Proposed that all the stuff in the world is “atomos” Proposed that all the stuff in the world is “atomos” Tiny, indivisible particles Tiny, indivisible particles Aristotle Aristotle Questioned theory of Democritus Rejected it for lack of proof

7 Roger Bacon Lived in 13th century Lived in 13th century Believed that science should be based on experimental evidence. Believed that science should be based on experimental evidence.

8 ALCHEMISTS Tried to turn base metals into precious metals. Tried to turn base metals into precious metals. Developed knowledge and techniques Developed knowledge and techniques Not true scientists Not true scientists

9 Copper into Gold Laboratory Alchemists tried to turn normal copper into gold coins! Alchemists tried to turn normal copper into gold coins! If they succeeded, they would never need to work! If they succeeded, they would never need to work!

10 Prove that the coins are GOLD How is copper different than gold? How is copper different than gold? How can you test it? How can you test it? What techniques are you using…that Democritus did not use? What techniques are you using…that Democritus did not use?

11 Antoine Lavoisier 1743-1794 1743-1794 French French Father of Chemistry Father of Chemistry Sadly, beheaded in French Revolution Sadly, beheaded in French Revolution

12 Lavoisier LAW OF CONSERVATION OF MATTER LAW OF CONSERVATION OF MATTER Matter, like energy, is neither created nor destroyed in a chemical reaction. Matter, like energy, is neither created nor destroyed in a chemical reaction. This concept established modern chemistry. This concept established modern chemistry.

13 What was different? Experimentation Experimentation He used a balance to study the role of oxygen in rusting and burning.

14 Other people did it, too! Priestly did similar experiments. Priestly did similar experiments. He believed a false theory of Phlogiston. He believed a false theory of Phlogiston. Kept his mind closed to new idea. Kept his mind closed to new idea.

15 PROUST 1799 1799 Law of Constant Composition Law of Constant Composition A given compound always contains the same elements in the same proportion by mass. WATER 11% Hydrogen WATER 89% Oxygen

16 JOHN DALTON LAVOISIERPROUST DEMOCRITUS BACON ATOMIC THEORY OF MATTER

17 DALTON’S ATOMIC THEORY OF MATTER 1.All matter is composed of submicroscopic (extremely small) indivisible particles called ATOMS. 2.All atoms of a given element are identical. The atoms of any one element are different from those of any other element.

18 DALTON’S ATOMIC THEORY OF MATTER 3.Atoms are neither created nor destroyed in a chemical reaction. Chemical reactions occur when atoms are separated, joined, or rearranged. However, atoms of one element are never changed into atoms of another element as a result of a chemical reaction.

19 DALTON’S ATOMIC THEORY OF MATTER 4.Atoms of different elements can mix physically or can combine chemically with one another in simple whole number ratios to form compounds.

20 What does this mean? Atomic Theory of Matter Not perfect... but a workable theory to build on.

21 Scientists had been doing many experiments with electricity since Ben Franklin flew his kite. Scientists had been doing many experiments with electricity since Ben Franklin flew his kite. Faraday suggested that electricity might explain the atom Faraday suggested that electricity might explain the atom English physicist, J.J. Thomson 1856-1940 English physicist, J.J. Thomson 1856-1940 Discovered electrons in 1897 Discovered electrons in 1897 Thomson experimented with a “cathode ray tube” Thomson experimented with a “cathode ray tube”

22 Cathode Ray Tube

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24 Thomson’s Cathode Ray Tube Experiment Flow of electric current through gases. Flow of electric current through gases. Sealed gas in glass tube with metal plates at the end. Sealed gas in glass tube with metal plates at the end. Connected plates to high voltage source: Connected plates to high voltage source: Anode + and Cathode – Anode + and Cathode –

25 This ray could be deflected toward a positive charge… It has a negative charge. This ray could move things… It was made of particles of matter. This ray acted the same no matter what materials were used… It was not atoms…it must be part of all atoms

26 Cathode Ray Tube Cathode ray is composed of very small negatively charged particles that are part of atoms ELECTRONS

27 Cathode Ray Tube

28 Diagram of CRT

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31 Atomic Theory Millikan devised experiments to determine the mass and charge of the electron. Millikan devised experiments to determine the mass and charge of the electron. Protons : discovered in 1886 Protons : discovered in 1886 Positively charged particles Also discovered with cathode ray tube…these particles went the other direction. Also discovered with cathode ray tube…these particles went the other direction.

32 The Nuclear Atom Rutherford Rutherford Identified three types of radiation Identified three types of radiation Alpha…positive particle Alpha…positive particle Beta…negative particle Beta…negative particle Gamma…high energy Gamma…high energy Devised the GOLD FOIL EXPERIMENT Devised the GOLD FOIL EXPERIMENT Now…where were we….?

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37 Rutherford’s Nuclear Atom Most of the mass of an atom is in the center…the nucleus…with electrons moving around it. Most of the mass of an atom is in the center…the nucleus…with electrons moving around it.

38 Nuclear atom By 1932, neutron was discovered, too. By 1932, neutron was discovered, too. The nucleus is the central core of the atom, composed of protons and neutrons. Because, protons and neutrons have much greater mass than electrons, almost all of the mass of the atom is concentrated in a tiny nucleus…a dime in a football stadium! The nucleus is the central core of the atom, composed of protons and neutrons. Because, protons and neutrons have much greater mass than electrons, almost all of the mass of the atom is concentrated in a tiny nucleus…a dime in a football stadium!

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40 What next? We know the parts of the atom. We know the parts of the atom. We know about the nucleus. We know about the nucleus. What about the electrons? What about the electrons?

41 Bohr’s Model Light provided the next clues for the structure of the atom Light provided the next clues for the structure of the atom

42 Light has a Dual Nature Like this picture… Young lady or Old lady?

43 Light is a wave Electromagnetic radiation travels in waves.

44 As the wavelength increases, the frequency decreases. As the wavelength increases, the frequency decreases. The greater the frequency the greater the energy. The greater the frequency the greater the energy.

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46 Light acts like Particles Electromagnetic radiation also has the properties of particles. Electromagnetic radiation also has the properties of particles. Bohr suggested that energy is emitted and absorbed in discrete quantities called Bohr suggested that energy is emitted and absorbed in discrete quantities called Quanta or Quantum packets or pieces of energy “Jumps”

47 Demonstrate Quantum

48 Dual Nature of Light is the next tool for understanding the atom Energy is directly proportional to frequency…wave nature. Energy is directly proportional to frequency…wave nature. Einstein proposed that light consists of quanta of energy that behave like particles of light…he called these photons. Einstein proposed that light consists of quanta of energy that behave like particles of light…he called these photons. Example: photoelectric effect Example: photoelectric effect This is the DUAL NATURE OF LIGHT

49 Continuous Spectrum vs. Line Spectrum

50 What does this have to do with ATOMS? Atoms give off energy as photons of light. Atoms give off energy as photons of light. Line spectra of elements reveal that electrons exist in quantized (discrete) energy levels. Line spectra of elements reveal that electrons exist in quantized (discrete) energy levels. Rainbow…continuous spectrum Rainbow…continuous spectrum Line…discontinuous spectrum Line…discontinuous spectrum The color allows us to calculate the energy The color allows us to calculate the energy higher frequency = higher energy… higher frequency = higher energy… purple higher than red purple higher than red

51 Emission Spectra Line Spectra of elements show discrete or quantized energy levels in the atom. Line Spectra of elements show discrete or quantized energy levels in the atom. These energy levels are different for each element. These energy levels are different for each element. The color or wavelength of light shows the energy level because energy can be calculated from frequency of light emitted. The color or wavelength of light shows the energy level because energy can be calculated from frequency of light emitted.

52 Bohr’s Model of the Atom Bohr applied Quantum Theory to the structure of the hydrogen atom. Bohr applied Quantum Theory to the structure of the hydrogen atom. Quantum theory means that electrons jump from level to level. Quantum theory means that electrons jump from level to level. Bohr pictured the electrons spinning around set orbits, like planets around the sun. Bohr pictured the electrons spinning around set orbits, like planets around the sun. Planetary Model Planetary Model

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54 Quantum Leaps! Electrons exist at low energy… Electrons exist at low energy… ground state Add energy to go to higher energy… Add energy to go to higher energy… excited state Electron drops back down to ground state as soon as it can Electron drops back down to ground state as soon as it can It releases the exact energy it needed to jump up as a photon of a frequency or color. It releases the exact energy it needed to jump up as a photon of a frequency or color.

55 Schroedinger’s Quantum Mechanical (Today’s) Model We still have energy levels, like Bohr We still have energy levels, like Bohr Heisenberg Uncertainty Principle Heisenberg Uncertainty Principle It is impossible to know the velocity and position of a particle at the same time It is impossible to know the velocity and position of a particle at the same time We can not know the exact location of an electron. We can not know the exact location of an electron. Any effort to do so, will change the position. Any effort to do so, will change the position. We can only figure the probability of finding it in a certain region. We can only figure the probability of finding it in a certain region.

56 Orbitals Area where electrons are most likely to be found. Area where electrons are most likely to be found. Example: Example: If your mom wants you to do some work, she can find you in your room most of the time, or the house, or the yard…but you could be at the mall. And sometimes her efforts to find you, make you move!

57 Today’s Atom Dense, small,nucleus (with protons and neutrons) is surrounded by a fuzzy cloud shapes where electrons (that act more like waves) are most likely to be found… orbitals.

58 Today’s Model of the Atom aka Schroedinger’s or Quantum Mechanical Model

59 Links Go to Holt On-Line for a nice review of all this. my.hrw.com/ Go to Holt On-Line for a nice review of all this. my.hrw.com/ Go to this site to see some great atomic atrwork! Go to this site to see some great atomic atrwork!www.chemsoc.org/.../orbital/images/elev3.jpg

60 The Crazy World of Quantum Mechanics “If you aren’t shocked by it, you don’t understand it.” Bohr


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