Chapter # 4 Homework # 1 Second Marking Period: 10/19/16

II MARKING PERIOD Homework # CH 4: 1 A Democritus John Dalton William Crookes J.J. Thompson Robert Millikan

6. Rutherford Model 7. Erwin Shroedinger 8. James Chadwick 9 6. Rutherford Model 7. Erwin Shroedinger 8. James Chadwick 9. The Bohr Model 10. The Wave Mechanical Model

10/19/16 Aim #1: How was the structure of the atom developed?

http://www.csun.edu/science/courses/619/flash/models_of_atom.swf

How can you describe an atom?

How do we know about the atom?

Thomson Dalton Rutherford

Chadwick Bohr Erwin Shroedinger

1. 400 B.C. Ancient Greek Philosophy FIRE AIR Everything in the universe is made of one or more of the basic “elements:” WATER EARTH

2. Democritus (2,000 years ago) The atom is made up of so small and indestructible particles. Atoms: Indivisible. Atoms are homogenous. Atoms differ in size, shape, mass, position, and arrangement.

3. John Dalton’s Atomic Theory (1803) Elements are made of atoms Atoms of an element are the same. Compounds are formed from combinations of atoms. In chemical reactions, atoms combine in small, whole-number ratios. John Dalton

Dalton’s View of an atom 1803

4. William Crookes (1870s) Something travels from the cathode “cathode rays” Cathode Rays consist of electrical charged particles

5. J.J. Thomson (1856-1940) 1897 Discovered the electron and developed “The plum-pudding model of the atom.”

http://highered. mcgraw-hill. com/olcweb/cgi/pluginpop. cgi http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::100%::100%::/sites/dl/free/0072512644/117354/01_Cathode_Ray_Tube.swf::Cathode%20Ray%20Tube

Cathode-rays are deflected by electric or magnetic fields. Cathode-rays are particles Cathode-rays are what we know as electrons

J.J. Thomson’s Model of the Atom “Plum pudding” model: Negative electrons are embedded in a positively charged mass.

6. Robert Millikan: 1908 found out the electric charge of the electron Famous experiment called the “oil-drop experiment”

The Oil Drop Experiment http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::100%::100%::/sites/dl/free/0072512644/117354/02_Millikan_Oil_Drop.swf::Milikan%20Oil%20Drop

7. Rutherford Model (1909) http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf

7. Rutherford Model (1909)

7. Rutherford Model (1909) “Gold Foil experiment” Bombarded gold foil with alpha particles (+). Most of the atom is empty space with small, dense positively charged nucleus.

Rutherford’s Model

http://micro.magnet.fsu.edu/electromag/java/rutherford/index.html

8. Erwin Shroedinger: 1926 Erwin Shroedinger (1926), Austria - introduced the Shroedinger Equation, a wave equation that describes the form of the probability waves that govern the motion of small particles and how these waves are altered by external influences.

9. James Chadwick: The Neutron Chadwick (1931), discovered the neutrally-charged neutron.

10. The Bohr Model (1913) Neil Bohr pictured the atom as having a positively charged nucleus and negatively charged electrons in specific orbits.

Bohr’s Model

Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons. Niels Bohr 1913

electrons in orbits nucleus

http://www. yteach. co. uk/index http://www.yteach.co.uk/index.php/resources/atom_atomic_spectra_emission_line_electromagnetic_energy_Bohr_model_radiation_page_4.html

11. The Wave Mechanical Model Small, dense, nucleus positively charged nucleus surrounded by electrons moving in “electron cloud”. “Orbitals” are areas where an electron with a certain amount of energy is most likely to be found.

The quantum theory is the most up-to-date theory of the times The quantum theory is the most up-to-date theory of the times. Its' model of the atom explains its stability and like Bohr's Model, treats atoms as electrons surrounding a nucleus. The electrons, however, do not have a planetary orbit. Instead, the theory gives the location of an electron as a probability instead of showing it at a certain position.

The easiest way to describe the differences between the allowed and prohibited positions of electrons in an atom is to think of the electron as a wave. The wave-particle duality of quantum theory allows electrons to be described as waves, instead of particles. Keep in mind that this theory may be disproved in the near future and replaced with a new model with even more complicated mathematical calculations.

End of the show

Antoine Henri Becquerel (1852-1908)

Antoine Henri Becquerel (1852-1908) It was the month of February in the year of 1896. Antoine Henri Becquerel, a French scientist, was conducting an experiment which started with the exposure of a uranium-bearing crystal to sunlight. Once the crystal had sat in the sunshine for a while, he placed it on a photographic plate. As he had anticipated, the crystal produced its image on the plate. Becquerel theorized that the absorbed energy of the sun was being released by the uranium in the form of x-rays.

Further testing of this theory had to be put off for a few days because the sky had clouded up and the sun had disappeared. For the next couple of days he left his sample of uranium in a closed drawer along with the photographic plate.

How could this be. There was no source of energy to produce the image How could this be? There was no source of energy to produce the image! What Becquerel had discovered was that a piece of mineral which contained uranium could produce it's image on a photographic plate in the absence of light. What he had discovered was radioactivity! He attributed this phenomenon to spontaneous emission by the uranium.