Presentation on theme: "Chemistry 4.1 Section 4.1-2 Defining the Atom Part II."— Presentation transcript:
1Chemistry 4.1Section 4.1-2Defining the AtomPart II
2Defining the Atom4.1-2Cathode-ray tubes are found in TVs, computer monitors, and many other devices with electronic displays.
3Models of the Atom – II: Michael Faraday 4.1-2Models of the Atom – II: Michael Faraday1839: English Chemist Michael FaradaySuggested that the structure of atoms was somehow related to electricity. He proved that atoms contain particles that have electrical charges.Questions about electricity and charges on particles were answered in a few short years using a device called a Cathode Ray Tube or CRT.
4Models of the Atom – II: Eugen Goldstein 4.1-2Models of the Atom – II: Eugen Goldstein1886: German Physicist Eugen GoldsteinIn 1886, Eugen Goldstein observed a cathode-ray tube and found rays traveling in the direction opposite to that of the cathode rays. He concluded that they were composed of positive particles.Such positively charged subatomic particles are called protons.4
5Models of the Atom – II: JJ Thomson 4.1-2Models of the Atom – II: JJ Thomson1897: English Physicist J. J. ThomsonIn 1897, the English physicist J.J. Thomson (1856–1940) discovered the electron using a cathode ray tube (CRT). Electrons are negatively charged subatomic particles.5
6Models of the Atom – II: J. J. Thomson 4.1-2Models of the Atom – II: J. J. ThomsonThomson performed experiments that involved passing electric current through gases at low pressure.The result was a glowing beam, or cathode ray, that traveled from the cathode to the anode.6
7Models of the Atom – II: J. J. Thomson 4.1-2Models of the Atom – II: J. J. ThomsonCathode Ray Tube7
8Models of the Atom – II: J. J. Thomson 4.1-2Models of the Atom – II: J. J. ThomsonA cathode ray is deflected by a magnet.8
9Models of the Atom – II: J. J. Thomson 4.1-2Models of the Atom – II: J. J. ThomsonA cathode ray is deflected by electrically charged plates.9
10Models of the Atom – II: J. J. Thomson 4.1-2Models of the Atom – II: J. J. ThomsonUsing a CRT, Thomson discovered the following:A cathode ray is a stream of electrons.Electrons are parts of the atoms of all elements.Both magnetic and electrical fields deflect the ray’s path in a CRT in a mathematically predictable way.Changing the gas or the material that the plates were made of effected his results.10
11Models of the Atom – II: J. J. Thomson 4.1-2Models of the Atom – II: J. J. ThomsonFrom this, Thomson proposed the following:Cathode rays are made up of “-” charged particles.Particles in a CRT came from the cathode plate.Atoms are not invisible balls, but had structure.Called these negative particles “Electrons”.Calculated the ratio of the electron’s charge to its mass.Developed the atomic model called “Plum Pudding”.11
12Models of the Atom – II: J. J. Thomson 4.1-2Models of the Atom – II: J. J. ThomsonThomson’s Plum Pudding Model:J. J. Thomson’s model of the atom, he called “Plum Pudding” (that’s what it reminded him of) had a “sea of positive charge” called the nucleus with electrons scattered throughout the atom’s positively charged interior.However, this model did not last very long.12
13Models of the Atom – II: Henri Becquerel 4.1-2Models of the Atom – II: Henri Becquerel1896: French Physicist Henri BecquerelWhile working with Marie Curie and her husband, Pierre, accidentally discovered radiation. He accidentally placed a piece of potassium uranyl sulfate (radioactive material) on an unexposed film plate. He went to use the film plate, and when he developed the plate, all he saw was the outline of the material.13
14Models of the Atom – II: Henri Becquerel 4.1-2Models of the Atom – II: Henri BecquerelBecause of his work, along with the work of Marie and Pierre Curie, all three received the Nobel Prize in Physics.Photographic Plate showing Radioactivity14
15Models of the Atom – III: Robert Millikan 4.1-2Models of the Atom – III: Robert Millikan1909: American Physicist Robert MillikanPerformed the famous “Oil Drop” experiment in order to measure the electrical charge on an electron.Unlike his colleagues before him, Robert Millikan was able to determine the charge of an electron using his famous “Oil Drop” experiment.
16Models of the Atom – III: Robert Millikan 4.1-2Models of the Atom – III: Robert MillikanRobert Millikan’s Oil Drop Experiment16
17Models of the Atom – III: Robert Millikan 4.1-2Models of the Atom – III: Robert MillikanThe oil drop experiment was an experiment performed by Robert Millikan and Harvey Fletcher in 1909 to measure the electrical charge of an electron.The experiment entailed balancing the downward gravitational force with the upward bouyant and electric (charged) forces on tiny charged droplets of oil suspended between two metal electrically charged plates or electrodes.By repeating the experiment for many droplets, they were able to confirm that the charges were all multiples of some fundamental value, and calculated it to be the charge of a single electron.17