-+Structure+of+the+Nuclear+Atom

toc =- J.J. Thomson electrons (cathode ray tube)= J.J. Thomson and Electrons (Cathode Ray Tube)

Electrons – - negatively charged - they have a -1 charge - they have a mass of 9.11 x 10^-25 - discovered by J.J. Thomson in 1897 - located in the electron cloud surrounding the nucleus Discovery of the Electron: Joseph John Thomson used a cathode ray tube to deduce the presence of a negatively charged particle known as THE ELECTRON The cathode ray tube was discovered by Willliam Crookes

The Modern Cathode Ray Tube = Modern CRT - television and computer monitors are modern cathode ray tubes - CRT’s pass electricity through gas contained in very low pressure

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=- Robert A. Millikan's Oil Drop Experiment=


 * //__ Robert Millikan’s Oil Drop Experiment __//**

 In 1909, through the experiment that this film clip so masterfully elucidates, Robert Millikan determined the charge of electrons. When a thin stream of oil droplet particles was allowed to flow in a chamber between and negatively charged plates, and when x-rays passed through that chamber (since x-rays can bring about a charge when they strike matter), those particles all had charges (when voltage was on) that were multiples of a single, incredibly small negative value. From this, Millikan concluded that that tiny value was the charge of a single electron. Thus determining that the electric charge on electrons was negative.





=- Eugen Goldstein and protons=


 * Eugen Goldstein – in 1886: “proton” have positive charge, positive charge, relative mass of +1 (or 1840 times that of an electron


 * **Eugen Goldstein ****, ** (b. Sept. 5, 1850, Gleiwitz, Prussia—d. Dec. 25, 1930, Berlin), German physicist known for his work on __ electrical __ phenomena in gases and on cathode rays; he is also credited with discovering canal rays. He was primarily interested in electrical discharges in moderate to [|**__high vacuums__**]. In 1886 he discovered what he termed //Kanalstrahlen,// or canal rays, also called positive rays; these are positively charged ions that are accelerated toward and through a perforated cathode in an evacuated tube. He also contributed greatly to the study of cathode rays; in 1876 he showed that these rays could cast sharp shadows, and that they were emitted perpendicular to the cathode surface. This discovery led to the design of concave cathodes to produce concentrated or focused rays, which became fundamental to numerous __ experiments __. [[image:eugen_goldstein.jpg width="287" height="304"]]media type="youtube" key="cnXV7Ph3WPk?fs=1" height="385" width="480"
 * 

=- James Chadwick and neutron= media type="youtube" key="oKM8uJrcmyk?fs=1" height="385" width="480" James Chadwick: -Physicist -Won nobel prize in 1935 - In 1932, James Chadwick proved that the atomic nucleus contained a neutral particle which had been proposed more than a decade earlier by Ernest Rutherford.

Read more at Suite101: [|**The Discovery of the Neutron: James Chadwick's Remarkable Experiment**] [|**http://www.suite101.com/content/the-discovery-of-the-neutron-a46060#ixzz15S20n353**] -He completed the atomic model

Neutrons: -A subatomic particle with no net charge -It’s neutral -Its mass is slightly larger than that of a proton -They live in the nucleus of an atom with protons -Are important in nuclear energy and explosions -Mass = 1.67 x 10-24 -Zero average mass unit (amu) -Mass number – atomic number = number of neutrons

=- Rutherford's Gold-Foil Experiment=

=- Thomson's Plum-Pudding Atomic Model=

__Thomson:__

 * Was a Physicist
 * Discovered the electron and isotopes
 * Created the "Plum-Pudding Atomic Model"

__Plum-Pudding Atomic Model:__

 * In the model, the atom is made up of electrons (or "corpuscles") surrounded by a soup of positive charge to create equilibrium with the electrons' negative charges.
 * Negatively charged "plums" surrounded by positively charged "pudding"
 * The model was disproved by Rutherford's Gold Foil Experiment



=- Half-Life=

A half-life is the time required for one-half of the nuclei of a radioisotope sample to decay to products. **After each half-life, half of the existing radioactive atoms have decayed into atoms of a new element.** 

For example, the chart below displays how a **carbon-14** isotope decays with each half-life:


 * **Years** ||  **Amount of Isotope Remaining (g)**  ||
 * 0 ||  2.00 x 10^-12  ||
 * 5730 ||  1.00 x 10^-12  ||
 * 11460 ||  0.500 x 10^-12  ||
 * 17190 ||  0.250 x 10^-12  ||

 As you can see, each half-life is 5730 years. With each half-life, the amount of the isotope remaining decays to a half of what it was previously.