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Chemistry - Atomic Theory - Ch 4 (Scientists (Dalton (1700-1800s) (ALL…
Chemistry - Atomic Theory - Ch 4
Scientists
Rutherford (1800-1900s)
GOLD FOIL EXPERIMENT
ALPHA particles (positive charged helium) directed at a thin sheet of gold
most alpha particles
went straight through, or were slightly deflected - and
Some even bounced back to the source
bounced off at very large angles
New theory - nuclear atom
atom is mostly empty space
all the positive charge and
almost all of the mass are concentrated
Thomson (1800-1900s)
ELECTRONS
negatively charged
sub-atomic
particles
EXPERIMENT
cathode ray - traveled from cathode to anode
the cathode ray -
deflected
by
negative
plate, attracted to the positive one
constant ratio
// charge to mass ratio of electrons - not dependent on the gas or metal so
all elements have electrons
Dalton (1700-1800s)
ALL elements are composed of
atoms
Same
elements' atoms are identical AND
different
elements' atoms are different from other element
Atoms of different elements can
mix
physically
,
combine
chemically
in
simple whole-number ratios
=
compunds
Chemical reactions = atoms are
separated
from each other,
joined
, or
rearranged
in different combinations.
Atoms of one element are
never changed into atoms of another element
as a result of a chemical reaction.
Democritus
atoms were
indivisible and indestructible
Atomic number
number of protons
identifies the element
mass number
number of neutrons and protons