Scientists & their Experiments

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J. J. Thomson >Cathode Rays >electron

English physicist from Cambridge

Constructed a partially glass tube and applied a high electrical voltage between 2 electrodes at either end of the tube. He found a beam of particles (called cathode rays) traveled from the negatively charged electrode (called cathode) to the positive charge (called anode).

Particles composing the cathode rays had these properties:

traveled in straight lines

independent of the material that they originate, cathode

carry a negative electrical charge

Cathode ray: a stream of electrons produced when a high electrical voltage is applied between two electrodes with a partially evacuated tube

Cathode ray tube: an evacuated tube containing charged plates to accelerate and view electron beams

Measured the 'charge-to-mass' ratio of the cathode ray particles by deflecting them with electric and magnetic fields by seeing the strengths at which the effect of the two fields cancel

Discovered the electron!

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Robert Milikan >Oil Drop

>Electron charge

American physicist in 1909

sprayed oil into fine droplets as an atomizer, they fell rough a small hole into the lower level. during the fall the drops gathered electrons, these electrons had been produced with the air let into the chamber with ionizing radiation. the lower part of the apparatus had a negatively charged electric field. by measuring the strength of the electric field required to stop the free fall of the drops, he figured out the masses/charge of the drops

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Henri Becquerel&Marie Curie

>radioactivity

discovered radioactivity

the element Curium was named after Curie for discovering it

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Ernest Rutherford >Gold Foil

disapproved Thomson's model of the atom

directed positively charged alpha particles at an ultrathin gold foil sheet to act as probes of the gold atom's structure

most particles passed directly through the foil, while some bounced back

>Nuclear Atom >Nuclear Theory

the results from his gold foil experiment lead Rutherford to create the model of the atom containing a dense nucleus and electron cloud

Majority of the atom's mass/all positive charge is in the nucleus

Most volume is empty space where electrons are dispersed

Amount of electrons and protons are equal

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James Chadwick >neutrons

In trying to account for the remaining mass in an atom after accounting for all its known parts, they discovered the neutron

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Dmitri Mendeleev> Periodic Law

Russian chemist

noticed similarities in the element's properties

listed them in order of increasing mass

predicted elements yet to be discovered

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Clemens Winkler>germanium

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Mass Spectrometer

mass spectrometer: an experimental method of determining the precise mass and relative abundance of isotopes

Sample is injected into vaporizing part of instrument

Vaporized atoms are ionized by an e- beam

e- in beam collide with the atoms-- removing e- and creating positively charged ions

Ion move to a magnetic field that bends their trajectory

the amount of bending depends on the mass of the ions; bending the lighter ions more than heavier ones

three paths lie around the corner measuring the bend/mass of the ion

they strike a detector d make an electrical signal

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Avogadro >number

Amedeo Avogadro Italian physicist discovered the mole (mol): the amount of a substance

6.02214 x 10^23 (rounded to 4sf)

1 mole C ats = 12 g C = 10^23 C ats

gives a relationship between mass (grams of C) and number of atoms (Avo's #)