Presentation on theme: "Dear students, How are you, we hope that you all are fine especially after this long.long vacation. It is time to work, we try always to offer you the."— Presentation transcript:
Dear students, How are you, we hope that you all are fine especially after this long.long vacation. It is time to work, we try always to offer you the best. Now hoping that you too will do your best to pass this critical period of time & to complete together our success. For better future to our country. Science Department
1- Greek philosophers Substances consists of smaller particles which are indivisible called A toms A = no tom = divide
Aristotle Aristotle Aristotle fire air water Dust He rejected the concept of atom ** He said that ** Matter consists of 4 main components which are.
It was believed that cheap metal as Iron or Copper Can be changed into precious ones as gold by change the ratio of constituent
3- Boyle He refused Aristotle's idea & give the 1 st definition of the element Element Simple pure substance that can not be changed into simpler form by traditional chemical method
Whos Next? n Late 1700s - John Dalton- England. n Teacher- summarized results of his experiments and those of others. n Elements substances that cant be broken down n In Daltons Atomic Theory n Combined idea of elements with that of atoms.
Daltons Atomic Theory a- The matter is composed of very minute particles which is named atoms b- The atom is solid undivided particle c- The atoms of each element are different from the atoms of any other element
5 – Thomson Gases do not conduct electricity under normal conditions of pressure & temperature
Cathode rays are the carriers of electric current from cathode to anode inside a vacuumed tube The condition at which the gas could be conduct electricity Discharge tube with a- Pressure ranges between 0.01 – 0.001 mm Hg b- Potential difference of about 10,000 volts was applied through the space between the
Thomsons Experiment Voltage source +- Metal Disks
n Passing an electric current makes a beam appear to move from the negative to the positive end Thomsons Experiment Voltage source +-
Thomsons Experiment n By adding an electric field he found that the moving pieces were negative + - n By adding an electric field
G.R.F To get the cathode rays, the used tube is discharged to a very low pressure. Because gases do not conduct electricity Under normal pressure
Cathode rays A stream of electrons produced at the ( -ve ) electrode ( cathode ) of the vacuum glass tube containing a gas at low pressure
Properties of cathode rays 1-A stream of electrons produced at the ( -ve ) electrode ( cathode ) of the vacuum glass tube containing a gas at low pressure 2-It moves in straight lines. 3-They have thermal effect. 4-They are affected by both electric & magnetic fields Chemist. Ahmed elfekey
Voltage source + - 5-They are negatively charged. 6-They do not differ either in behavior or in nature if the material of cathode or the used gas are changed [ Fundamental constituent of any matter ]
Rutherfords Experiment n Ernest Rutherford English physicist. (1910) n Believed the plum pudding model of the atom was correct. n Wanted to see how big they are. n Used radioactivity. n Alpha particles - positively charged pieces given off by uranium. n Shot them at gold foil which can be made a few atoms thick.
Rutherford, Geiger, and Marsden (Early 20th Century) Positively charged alpha-particles were directed at a piece of thin gold foil
Lead block Uranium Gold Foil Metal sheet coated With ZnS Chemist. Ahmed elfekey
1- The nucleus Central Much smaller than the atom There is vast ( large ) space between the nucleus & the orbits of electrons The atom is not uniformly dense Most of the atomic mass & the ( + ve ) charge are concentrated in the nucleus
2- Electrons The mass of electrons are negligible to that of the nucleus Atomic Number : Number of protons = Number of electrons Mass Number : Number of protons + Number of neutrons The Atom Nucleus electrons protons + neutrons ( - ) ( + ) (zero)
Objection on Rutherford's atomic model Maxwell's theory When an electrically charged particle moves in an orbit it will lose its energy gradually by emission of radiation resulting In gradual decrease in the orbit radius
G.R.F The radius of charged particle decrease gradually during its rotation in an orbit Because by applying Maxwell's theory When an electrically charged particle moves in an orbit it will Lose its energy gradually by emission of radiation resulting In gradual decrease in the orbit radius.
n Draw below a model of the atom proposed by the following individuals: Dalton Thomson Rutherford