Download Guided notes: Part II: History of the atomic theory

Name:
Date:
Hour:
Guided notes: Part II: History of the atomic theory
I. General atom info:
A. Atoms are fantastically durable. Because they last so long, atoms really
get around!
B. Every atom you possess has almost certainly passed through several
_________and been part of millions of ______________ on its way to
becoming you.
C. Nowadays, with the use of _____________ electron microscopes, we can
sort of “see” atoms…
These electron microscopes were invented in the mid-1900’s. How did
scientists _______________ _____ atomic structure without being able to
look at any atoms?
II. Development of atomic theory
A. What is a theory in science?
A theory is a well-tested explanation of what happens in nature.
In layman’s terms, if something is said to be “just a theory,” it usually means
that it is a mere _________, or is unproven. But in scientific terms, a theory
implies that something has been _________________ and ______________
many times by _______________________ groups of scientists.
A scientific law is a statement of something that seems to be _______ in the
natural world.
Example: The Law of Gravity. Newton could use this law to predict the
behavior of a dropped object, but he couldn't ____________ why it happened.
A law states or describes __________ happens in nature.
A theory explains _______ it happens.
Both are well-tested by _______________.
Memory hint: “explanation starts with an “____” and “___________” has an
“e”.
III. Important Historical Figures
A. Democritus
•
first to suggest that matter is made of tiny particles called
“__________”
•
•
•
“atomos” = Greek for “______________________”
ideas were rejected by ____________, who was very influential, and
therefore forgotten for two thousand years.
ancient Greek _______________, not scientist
Democritus’ atomic model:
atoms were small, hard particles that were different ___________ and _______
C. John Dalton:
First to propose an atomic theory
based on __________:
**You’ll need to know each of these four parts of his theory
1. Each element is composed of small ___________ called atoms.
2. All atoms of a given element are ______________*; the atoms of
different elements are __________________.
3. Atoms are not ______________ or _____________ in chemical reactions.
4. ________________ are formed when atoms of more than one element
__________.
Dalton’s atomic model:
a tiny ____________ that is ________________
D. J.J. Thompson
• First to suggest that there were particles ____________ than the atom.
• Discovered the ______________.
• Developed the “plum pudding model.”
Thomson’s “plum-pudding” model:
the atom is composed of electrons surrounded by a _____________of
_____________ charge to ______________ the electron's negative charge
E. Ernest Rutherford
• __________ foil experiment
• discovered the ____________, and realized that it was very ________
and _______________ charged
• suggested that most of the atom is empty _____________
Gold Foil Experiment:
Rutherford shot tiny positively-charged __________ particles through a thin
sheet of gold foil
Gold Foil Experiment:
Some of the alpha particles _________________ ___________. “It was as if you
fired a 15-inch cannon ball at a piece of tissue paper and it came back and hit
you.”
Such huge __________________ could mean only one thing: some of the alpha
particles had run into massive concentrations of ___________ charge and, since
like charges _____________ had been hurled straight back by them
Rutherford’s atomic model:
All of the positive charge is crammed inside a tiny, massive ___________about
______ __________________ times smaller than the atom as a whole. The
atom is mostly empty _______________.
F. James Chadwick
•
Scientists were looking for missing ______ – the ___________
and ____________ in the atom didn’t __________ enough to account for
the mass of the atom
proved the existence of _____________
•
•
Protons and neutrons are in the ____________, which only takes up one
_______________ of a ______________ of the volume of the atom. The
electrons are in the electron __________, which constitutes almost all of the
volume of the atom.
In fact, if an atom were expanded to the size of a cathedral,
the nucleus would be about the size of a _____________