Our current class model of the atom John Dalton’s Model element Molecule/compound Element/molecule All matter is made of atoms Smallest form of matter.

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Presentation transcript:

Our current class model of the atom John Dalton’s Model element Molecule/compound Element/molecule All matter is made of atoms Smallest form of matter Atoms are believed to be indivisible (nothing smaller than an atom) “Billiard ball” model

Cathode Ray Tube Experiment JJ Thomson (1897) Cathode: negatively charged electrode (attracts positively-charged things) Anode: Positively charged electrode (attracts negatively-charged things) cathode anode Majority of gas (air) inside tube is pumped out

Cathode Ray Tube Experiment The identity of this cathode ray was a topic of research/discussion for more than 40 years No one knew what it was! Many ideas emerged, but explanation began with the question of whether or not this cathode ray had an electric charge In order to find out, it seemed reasonable to place it within an electric field

Electric plates are charged Cathode ray is attracted to positive electrode This can only mean that the cathode ray is negatively charged

Thomson wanted to investigate the idea of the cathode ray having a charge even further by placing it in a magnetic field He knows that if something has a negative electric charge and its moving, a magnet will cause it to bend a certain way This provided further proof that whatever the cathode ray was composed of was most likely negatively charged

A few conclusions can be made… 1.) Cathode rays must be made of stuff that is negatively charged Was attracted to positively-charged anode Cathode ray bent in the direction Thomson predicted it would in the presence of a magnetic field Cathode ray bent in the direction toward positively-charged plate 2.) Particles that make up cathode rays are over 1,000 times smaller than a hydrogen atom Was able to determine the ratio of mass to charge and compare that to a hydrogen atom (smallest bit of matter known at the time) 3.) All different metals give off cathode rays Regardless of switching out different metals for the anode and cathode, Thomson found that the size of the stuff that made up the cathode rays was the same every time

To sum it up…. 1.) Cathode rays must be made of stuff that is negatively charged 2.) Particles that make up cathode rays are over 1,000 times smaller than the hydrogen atom 3.) All different metals give off cathode rays Atoms have tiny, negatively charged particles inside them Electrons!!

Time for a new model John Dalton’s Model Billiard ball model Smallest unit of matter Indivisible JJ Thomson’s Model Electrons are negative On the whole, atoms are usually neutral Because of this, there must be a positive charge within the atom to balance the negative “Plum Pudding” Model electron Positively charged “pudding”

cathode ray tube demo electrons have mass