Chapter 11: Atoms, Elements,   Compounds, and   Mixtures Table of Contents Section 3:  Compounds and Mixtures Section 1:  ...
<ul><li>Some of the early philosophers thought that matter was composed of tiny particles.   </li></ul><ul><li>They reason...
<ul><li>Eventually, you wouldn't be able to cut any more.  </li></ul><ul><li>You would have only one particle left.  </li>...
<ul><li>The early philosophers didn't try to prove their theories by doing experiments as scientist now do.  </li></ul><ul...
<ul><li>During the eighteenth century, scientists in laboratories began debating the existence of atoms once more.  </li><...
<ul><li>John Dalton proposed the following ideas about matter: </li></ul>Dalton's Concept Models of the Atom 1 <ul><li>Dal...
<ul><li>In 1870, William Crookes did experiments with a glass tube that had almost all the air removed from it.  </li></ul...
<ul><li>In the tube that Crookes used, the metal cathode was a disk at one end of the tube.  </li></ul>A Strange Shadow Mo...
<ul><li>When the battery was connected, the glass tube suddenly lit up with a greenish-colored glow.  </li></ul>A Strange ...
<ul><li>The shadow showed Crookes that something was traveling in a straight line from the cathode to the anode, similar t...
<ul><li>Crookes hypothesized that the green glow in the tube was caused by rays, or streams of particles.  </li></ul>Catho...
<ul><li>In 1897, J.J. Thomson placed a magnet beside the tube from Crookes' experiments.  </li></ul>Discovering Charged Pa...
<ul><li>Light cannot be bent by a magnet; therefore, Thomson concluded that the beam must be made up of charged particles ...
<ul><li>Thomson concluded that cathode rays are negatively charged particles of matter.  </li></ul>The Electron Models of ...
<ul><li>If atoms contain one or more negatively charged particles, then all matter, which is made of atoms, should be nega...
<ul><li>Could it be that atoms also contain some positive charge?  </li></ul>Thomson's Atomic Model Models of the Atom 1 <...
<ul><li>Thomson pictured a sphere of positive charge.  </li></ul>Thomson's Atomic Model Models of the Atom 1 <ul><li>The n...
Rutherford's Experiments Models of the Atom 1 <ul><li>In 1906, Ernest Rutherford and his coworkers began an experiment to ...
Rutherford's Experiments Models of the Atom 1 <ul><li>They wanted to see what would happen when they fired fast-moving, po...
<ul><li>Rutherford predicted that most of the speeding alpha particles would pass right through the foil and hit the scree...
<ul><li>There wasn't enough charge in any one place in Thomson's model to repel the alpha particle strongly.  </li></ul>Ex...
<ul><li>In Rutherford's experiment, alpha particles bombarded the gold foil. </li></ul>The Model Fails Models of the Atom ...
<ul><li>The uniform mix of mass and charges in Thomson's model of the atom did not allow for this kind of result.  </li></...
<ul><li>Rutherford thought that if the atom could be described by Thomson's model, as shown then only minor bends in the p...
The Proton Models of the Atom 1 <ul><li>Rutherford hypothesized that almost all the mass of the atom and all of its positi...
<ul><li>In 1920 scientists identified the positive charges in the nucleus as protons.  </li></ul>The Proton Models of the ...
<ul><li>Rutherford’s new model of the atom fits the experimental data.  </li></ul>The Proton Models of the Atom 1 <ul><li>...
<ul><li>In Rutherford's model, the only other particle in the atom was the proton.  </li></ul>The Neutron Models of the At...
<ul><li>It was proposed that another particle must be in the nucleus to account for the extra mass.  </li></ul>The Neutron...
<ul><li>The model of the atom was revised again to include the newly discovered neutrons in the nucleus.  </li></ul>The Ne...
<ul><li>Drawings of the nuclear atom don't give an accurate representation of the extreme smallness of the nucleus compare...
<ul><li>Even into the twentieth century, physicists were working on a theory to explain how electrons are arranged in an a...
<ul><li>Scientists soon learned that electrons are in constant, unpredictable motion and can't be described easily by an o...
<ul><li>Electrons travel in a region surrounding the nucleus, which is called the  electron   cloud .  </li></ul>The Elect...
1 Section Check Question 1 Explain why early Greek philosophers thought that matter was composed of atoms. NC: 1.05
1 Section Check Answer The early Greeks didn’t do experiments; they relied only on reasoning. They reasoned that if you ke...
1 Section Check Question 2 The first modern atomic theory was proposed by _______. A. Aristotle B. Dalton C. Rutherford D....
1 Section Check Answer The answer is B. John Dalton was a 19th century English school teacher. He thought atoms were tiny,...
1 Section Check Question 2 A cathode-ray tube has two electrodes, one at either end. These are known as the _______ and th...
1 Section Check Answer The answer is cathode and anode. Sometimes a cathode-ray tube is abbreviated to CRT. NC: 1.07
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Ch 11.1 Atomic Models

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Chapter 11:1 Atoms, Elements, Compounds, and Mixtures
Atomic Models - Democratis - Rutherford

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Ch 11.1 Atomic Models

  1. 1. Chapter 11: Atoms, Elements, Compounds, and Mixtures Table of Contents Section 3: Compounds and Mixtures Section 1: Models of the Atom Section 2: The Simplest Matter
  2. 2. <ul><li>Some of the early philosophers thought that matter was composed of tiny particles. </li></ul><ul><li>They reasoned that you could take a piece of matter, cut it in half, and continue to cut again and again. </li></ul>First Thoughts Models of the Atom 1
  3. 3. <ul><li>Eventually, you wouldn't be able to cut any more. </li></ul><ul><li>You would have only one particle left. </li></ul>First Thoughts Models of the Atom 1 <ul><li>They named these particles atoms. </li></ul>
  4. 4. <ul><li>The early philosophers didn't try to prove their theories by doing experiments as scientist now do. </li></ul><ul><li>Their theories were the result of reasoning, debating, and discussion—not of evidence or proof. </li></ul>Describing the Unseen Models of the Atom 1 <ul><li>Today, scientists will not accept a theory that is not supported by experimental evidence. </li></ul>
  5. 5. <ul><li>During the eighteenth century, scientists in laboratories began debating the existence of atoms once more. </li></ul><ul><li>Scientists came to realize that all matter is made up of elements. </li></ul>A Model of the Atom Models of the Atom 1 <ul><li>An element is matter made of atoms of only one kind. </li></ul>
  6. 6. <ul><li>John Dalton proposed the following ideas about matter: </li></ul>Dalton's Concept Models of the Atom 1 <ul><li>Dalton pictured an atom as a hard sphere that was the same throughout. </li></ul>1. matter is made up of atoms 2. atoms cannot be divided into smaller pieces 3. all the atoms of an element are exactly alike 4. different elements are made of different kinds of atoms
  7. 7. <ul><li>In 1870, William Crookes did experiments with a glass tube that had almost all the air removed from it. </li></ul>Scientific Evidence Models of the Atom 1 <ul><li>The glass tube had two pieces of metal called electrodes sealed inside. </li></ul><ul><li>The electrodes were connected to a battery by wires. </li></ul>
  8. 8. <ul><li>In the tube that Crookes used, the metal cathode was a disk at one end of the tube. </li></ul>A Strange Shadow Models of the Atom 1 <ul><li>In the center of the tube was an object shaped like a cross. </li></ul>
  9. 9. <ul><li>When the battery was connected, the glass tube suddenly lit up with a greenish-colored glow. </li></ul>A Strange Shadow Models of the Atom 1 <ul><li>A shadow of the object appeared at the opposite end of the tube—the anode. </li></ul>
  10. 10. <ul><li>The shadow showed Crookes that something was traveling in a straight line from the cathode to the anode, similar to the beam of a flashlight. </li></ul>A Strange Shadow Models of the Atom 1 <ul><li>The cross-shaped object was getting in the way of the beam and blocking it. </li></ul>
  11. 11. <ul><li>Crookes hypothesized that the green glow in the tube was caused by rays, or streams of particles. </li></ul>Cathode Rays Models of the Atom 1 <ul><li>These rays were called cathode rays because they were produced at the cathode. </li></ul><ul><li>Crookes' tube is known as a cathode-ray tube. </li></ul>
  12. 12. <ul><li>In 1897, J.J. Thomson placed a magnet beside the tube from Crookes' experiments. </li></ul>Discovering Charged Particles Models of the Atom 1 <ul><li>The beam was bent in the direction of the magnet. </li></ul>
  13. 13. <ul><li>Light cannot be bent by a magnet; therefore, Thomson concluded that the beam must be made up of charged particles of matter that came from the cathode. </li></ul>Discovering Charged Particles Models of the Atom 1
  14. 14. <ul><li>Thomson concluded that cathode rays are negatively charged particles of matter. </li></ul>The Electron Models of the Atom 1 <ul><li>He knew that opposite charges attract each other. </li></ul><ul><li>He observed that these particles were attracted to the positively charged anode, so he reasoned that the particles must be negatively charged. </li></ul><ul><li>These negatively charged particles are called electrons . </li></ul>
  15. 15. <ul><li>If atoms contain one or more negatively charged particles, then all matter, which is made of atoms, should be negatively charged as well. </li></ul>Thomson's Atomic Model Models of the Atom 1 <ul><li>But all matter isn't negatively charged. </li></ul>
  16. 16. <ul><li>Could it be that atoms also contain some positive charge? </li></ul>Thomson's Atomic Model Models of the Atom 1 <ul><li>The negatively charged electrons and the unknown positive charge would then neutralize each other in the atom. </li></ul><ul><li>Thomson revised Dalton's model of the atom. </li></ul>
  17. 17. <ul><li>Thomson pictured a sphere of positive charge. </li></ul>Thomson's Atomic Model Models of the Atom 1 <ul><li>The negatively charged electrons were spread evenly among the positive charge. </li></ul><ul><li>The atom is neutral. </li></ul>
  18. 18. Rutherford's Experiments Models of the Atom 1 <ul><li>In 1906, Ernest Rutherford and his coworkers began an experiment to find out if Thomson's </li></ul>model of the atom was correct.
  19. 19. Rutherford's Experiments Models of the Atom 1 <ul><li>They wanted to see what would happen when they fired fast-moving, positively charged bits </li></ul>of matter, called alpha particles, at a thin film of a metal such as gold.
  20. 20. <ul><li>Rutherford predicted that most of the speeding alpha particles would pass right through the foil and hit the screen on the other side. </li></ul>Expected Results Models of the Atom 1
  21. 21. <ul><li>There wasn't enough charge in any one place in Thomson's model to repel the alpha particle strongly. </li></ul>Expected Results Models of the Atom 1 <ul><li>That was a reasonable hypothesis because in Thomson's model, the positive charge is essentially neutralized by nearby electrons. </li></ul>
  22. 22. <ul><li>In Rutherford's experiment, alpha particles bombarded the gold foil. </li></ul>The Model Fails Models of the Atom 1 <ul><li>Most particles passed right through the foil or veered slightly from a straight path, but some particles bounced right back. </li></ul>
  23. 23. <ul><li>The uniform mix of mass and charges in Thomson's model of the atom did not allow for this kind of result. </li></ul>The Model Fails Models of the Atom 1
  24. 24. <ul><li>Rutherford thought that if the atom could be described by Thomson's model, as shown then only minor bends in the paths of the particles would have occurred. </li></ul>A Model with a Nucleus Models of the Atom 1
  25. 25. The Proton Models of the Atom 1 <ul><li>Rutherford hypothesized that almost all the mass of the atom and all of its positive charge are crammed into an incredibly small </li></ul>region of space at the center of the atom called the nucleus.
  26. 26. <ul><li>In 1920 scientists identified the positive charges in the nucleus as protons. </li></ul>The Proton Models of the Atom 1 <ul><li>A proton is a positively charged particle present in the nucleus of all atoms. </li></ul>
  27. 27. <ul><li>Rutherford’s new model of the atom fits the experimental data. </li></ul>The Proton Models of the Atom 1 <ul><li>This nucleus that contained most of the mass of the atom caused the deflections that were observed in his experiment. </li></ul>
  28. 28. <ul><li>In Rutherford's model, the only other particle in the atom was the proton. </li></ul>The Neutron Models of the Atom 1 <ul><li>That meant that the mass of an atom should have been approximately equal to the mass of its protons. However, it wasn't. </li></ul><ul><li>The mass of most atoms is at least twice as great as the mass of its protons. </li></ul>
  29. 29. <ul><li>It was proposed that another particle must be in the nucleus to account for the extra mass. </li></ul>The Neutron Models of the Atom 1 <ul><li>The particle, which was later called the neutron (NEW trahn), would have the same mass as a proton and be electrically neutral. </li></ul>Click image to view movie.
  30. 30. <ul><li>The model of the atom was revised again to include the newly discovered neutrons in the nucleus. </li></ul>The Neutron Models of the Atom 1 <ul><li>The nuclear atom, has a tiny nucleus tightly packed with positively charged protons and neutral neutrons. </li></ul>
  31. 31. <ul><li>Drawings of the nuclear atom don't give an accurate representation of the extreme smallness of the nucleus compared to the rest of the atom. </li></ul>Size and Scale Models of the Atom 1 <ul><li>For example, if the nucleus were the size of a table-tennis ball, the atom would have a diameter of more than 2.4 km. </li></ul>
  32. 32. <ul><li>Even into the twentieth century, physicists were working on a theory to explain how electrons are arranged in an atom. </li></ul>Further Developments Models of the Atom 1 <ul><li>It was natural to think that the negatively charged electrons are attracted to the positive nucleus in the same way the Moon is attracted to Earth. </li></ul>
  33. 33. <ul><li>Scientists soon learned that electrons are in constant, unpredictable motion and can't be described easily by an orbit. </li></ul>Further Developments Models of the Atom 1 <ul><li>They determined that it was impossible to know the precise location of an electron at any particular moment. </li></ul>
  34. 34. <ul><li>Electrons travel in a region surrounding the nucleus, which is called the electron cloud . </li></ul>The Electron Cloud Model Models of the Atom 1 <ul><li>The electrons are more likely to be close to the nucleus rather than farther away, but they could be anywhere. </li></ul>
  35. 35. 1 Section Check Question 1 Explain why early Greek philosophers thought that matter was composed of atoms. NC: 1.05
  36. 36. 1 Section Check Answer The early Greeks didn’t do experiments; they relied only on reasoning. They reasoned that if you kept cutting something in half, eventually you would have a piece so small it couldn’t be cut any more. NC: 1.05
  37. 37. 1 Section Check Question 2 The first modern atomic theory was proposed by _______. A. Aristotle B. Dalton C. Rutherford D. Thompson NC: 4.03
  38. 38. 1 Section Check Answer The answer is B. John Dalton was a 19th century English school teacher. He thought atoms were tiny, hard spheres. NC: 4.03
  39. 39. 1 Section Check Question 2 A cathode-ray tube has two electrodes, one at either end. These are known as the _______ and the _______. NC: 1.07
  40. 40. 1 Section Check Answer The answer is cathode and anode. Sometimes a cathode-ray tube is abbreviated to CRT. NC: 1.07

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