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Name:_________________________________________________Date:_____________Period:____
Notes #2: History of the Atom Parts 1&2
WHAT IS A MODEL?
● _____________ = an attempt to understand or explain things
● Usually things that are really ________ or really _____________
*** All models ____________________________________________! ***
● Over time, models become more _________________! Why??
➢ BECAUSE WE GET ________________________________________!!
DEMOCRITUS (460 - 370 B.C.)
● Credited for the first belief that atoms existed (atomic theory)
● But… ___________________!
ARISTOTLE (384 - 322 B.C.)
● Didn’t believe in ____________ (Democritus’ idea)
● Set us back __________________ :(
ANTOINE LAVOISIER (1770’s)
● Law of Conservation of ____________
○ Mass before = Mass after
JOSEPH PROUST (1797)
● Law of Definite Proportions
○ Each chemical compound has a ____________ and unchangeable ___________ of its
elements
● Ex: Water
○ Water always has ______________________ to every ___________________
○ ___________ = completely different compound!
JOHN DALTON (1803)
● Dalton’s ________________________
1. All matter is composed of atoms, which are indivisible and indestructible
2. All atoms of the same element are identical
3. All atoms of different elements are different
4. Compounds are composed of 2 or more different elements in a definite ratio
● Theory was easily accepted because he explained what people already knew….
________________________________________!
○ Law of Conservation of Mass = ___________________________
○ Law of Definite Proportions = __________________________
● Dalton’s atomic model:
J.J. THOMSON (1897)
● Electron discovery
○ _____________________________________ ​experiment
■ Stream of ____________________ aimed between 2 charged plates
■ Particles ____________________ away from negatively charged place, so they
must also have a ___________________ charge (= ____________________!)
● Plum Pudding Model
RUTHERFORD’S “GOLD FOIL” EXPERIMENT (1909)
● Conclusions…
○ _________________
1. Must be ____________________________ - only 1 in 20,000 particles
hit it
2. _______________________ charged (b/c of protons!) - positive
particles bounced off
3. Massive (________________) - was able to make particle bounce
backwards
NEW MODEL
● Atom is mostly _______________________________