Name: ___________________
Log # _____
ATOMIC THEORY NOTES
I. Atomic Theories
A. John Dalton 1803 Dalton’s Atomic Theory
1. One of the earlier scientists to work on the understanding of
2. Made four assumptions of Dalton’s Atomic Theory.
a. All Matter Consists of Tiny Particles Called Atoms.
i. The atom is the
smallest unit of an
chemical combination.
matter .
element that enters into a
b. Atoms Are Indestructible and Unchangeable
i. Atoms cannot be
created, destroyed, or transformed
atoms in a chemical change.
(a) Based on
the Law of Conservation of Mass
i. Means:
Mass can not change
into other
c. Elements are Characterized by the Mass of Their Atoms.
i. All atoms of the
same element have identical weights
ii. Atoms of
different elements
have different weights
.
d. When Elements React, Their Atoms Combine in Simple,
Whole-Number-Ratios.
i. Suggests a practical strategy for determining
relative atomic
weights from elemental percentages in
compounds .
3. Some of the details of Dalton’s original atomic theory are now known
to be
incorrect . But the core concepts of the theory are
of modern physical science.
foundations
Sep 17­6:50 PM
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B. Joseph J. Thomson 1906 Thomson’s Atomic Theory
1. Concluded after several experiments that
electrons
2. Believed that the
throughout the
electrons and protons
atom .
were part of every
atom .
were uniformly distributed
C. Ernest Rutherford 1909 Rutherford’s Atomic Theory
1. Conducted an experiment called the
“Gold Foil” Experiment
prove
J. J. Thomson incorrect
.
2. The experiment concluded that within an atom,
nearly all of the
mass of the atom
exist in a
stay a distance
away from the center
.
3. He named the positively charged center of the atom the
that would
the positive particles
central core
. While the
“nucleus”
and
electrons
.
a. Determined that the
nucleus was relatively small
compared to the
size of the
atom and that the
electrons dominated most of the space
of an
atom .
Sep 17­6:59 PM
2
D. Niels Bohr 1912 1. Found that
2. The shells
3. Atoms with
than those with
Bohr’s Atomic Theory
electrons exist in a set of
orbits around the nucleus
in which the electrons orbit
less than the maximum
"full" outer shells
.
hold only a certain number of electrons
number in their
outer shells
.
are less stable
.
4. Over the years other investigators
refined Bohr's theory, but his bold
application of new ideas paved the way for the development of
mechanics .
quantum
II. Atoms
A. Matter - anything that has
mass and takes up space
1. Made of tiny particles called
atoms.
2. Substances that contain only one type of atom are
elements
B. Three basic particles make up an atom:
protons , neutrons , and
electrons
1. Protons & Neutrons
make up the
nucleus of an atom.
a. Protons - particles have
positive electric charge
b. Neutrons - particles have
no electric charge
c. The nucleus has a
positive charge.
2. Electrons - Negative charged particles moving around the
nucleus
3. Atomic Number - The number of
protons in an atom's nucleus.
a. All atoms of the same element have the
same number of protons
b. This number also equals the number of
electrons in the
atom's electron cloud.
In a Neutral atom…
ATOMIC # = # of PROTONS = # of ELECTRONS
4. Mass Number - the number of
protons and neutrons making up an
atom's nucleus.
.
Sep 17­7:06 PM
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Sep 19­10:13 AM
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