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EVIDENCE FOR ATOMS AND
MOLECULES FROM GAS
BEHAVIOUS - DIFFUSION
Diffusion can be demonstrated in an experiment using
bromine.
1. Bromine liquid vaporises when phial in rubber tube is
broken and can move into other tube.
2. If the space in the tube is evacuated the brown colour of
bromine immediately fills the tube showing that the
atoms move at high speed.
3. If the space contains air the colour spreads slowly
because the bromine atoms collide with atoms and
molecules which make up the air. This also shows that
there is space for atoms and molecules to move between
each other.…read more

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EVIDENCE FOR ATOMS AND
MOLECULES FROM GAS
BEHAVIOUS ­ BROWNIAN MOTION
When smoke particles are suspended in air and viewed
under a microscope.
· Smoke particles are bombarded by atoms and molecules
in the air
· Atoms and molecules have momentum and exert a
force on the smoke particle
· Collisions are random and smoke particles are small
· At any time a resultant force exists as there are more
collisions on one side of the particle than the other
· The direction of the resultant force continually
changes direction and produces the random, jerky
motion.…read more

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MODELS OF THE ATOM
· Thomson suggested that an atom is like a
`plum pudding'
· Bohr suggested that the atom contained a
nucleus with electrons in orbit around it.…read more

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GEIGER AND MARSDENS ALPHA
PARTICLE SCATTERING
EXPERIMENT…read more

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Positively charged alpha particle were fired at thin gold foil, only slight
deflections were expected based on the plum pudding model,
however it was found that:
· Most of the alpha particles passed through with small deviations
· About 1 in 8000 particles were scattered more than 90° (so
deflected)
He concluded that:
· Most of the atom is empty space
· The atom must have a small nucleus containing most of the mass
of the atom
· The nucleus is positively charged with electrons in the space
around it.…read more

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