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A Brief History of AtomicTheory
This Section will focus on Scientistswho have had an impact on the
study of the atom.
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Democritus proposed that
matter cannot be broken
down indefinitely. At some
point you end up with apiece that cant be divided.
That smallest piece he
called an atom, from the
Greek word atomos, whichmeans indivisible.470-380 B.C.
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Democritus Model
Atomos
ATOMOS was the word Democritus used the
point, or stage where matter cannot be brokendown any further. ATOMOS literally means
indivisible
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John Dalton was aBritish chemist.He wasthe first modern
scientist to propose theexistence of atoms.Hedescribed an atom as aninvisible indestructible,solid sphere, like a
billiard ball.1766 - 1844
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Daltons Model
The Indivisible Sphere
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J.J. Thomson was a
British physicist who was
the first scientist to
propose the plum pudding
model. He was also the
first to propose the theory
of the negatively charged
electron. He was credited
for the discovery. He also
proposed the isotope.1856 - 1940
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Thomson plum pudding model
+
-
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Ernest Rutherford
experiments proved
that atoms are mostly
empty spaceDiscovered the nuclear,
which contains
positively charged
particles .Was the firstto suggest that
electrons circle the
dense nucleus.1871- 1937
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Rutherfords Model
Electron Negative charge
Nucleus
It has a
+ charge
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Niels Bohr stated that
electrons move in
different orbits, or
energy levels, around the
nucleus like planets orbit
the sun. Each energy
level is located a specific
distance from the
nucleus and contains acertain number of
electrons.
1885 - 1962
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Bohr Model
Electron-
negative charge
Energy
levels
Nucleus
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Current ModelThis model isbased upon Bohrs
model, except that
electrons orbit the
nucleus in random
patterns. The
region where theseparticles are found
is referred to as
the electron cloud.
Electron Clouds
Nucleus
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Demitri Mendeleev
Demitri Mendeleev was a
Russian scientist. He was
the first person to makethe periodic table. He also
wrote a chemistry
book.The periodic table is
a tool to help read
elements.
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Mendeleevs Table
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Modern Periodic Table
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How to Read the Table
6 2
C 4
carbon
12.01115
Atomic Mass
Number of
Electronsin each
energyfield
Atomic
Number
Chemical
Symbol
Element
Name
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Calculating Atomic Mass
6
CCarbon
12.01115
To find the Atomic
Mass, you look at the
bottom number in the
Atom tile and round itto the nearest whole
number.
Atomic
Mass
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How to find number of protons
6
CCARBON
12.01115
The number of Protons in
atom is also the Atomic
number, so therefore the
Atomic number also
represents the amount of
Protons in the nucleus of
that Atom.
Atomic Number/
number of Protons
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How to Find the Amount of
Neutrons in an AtomTo find the amount
of neutrons in an
atom you have tosubtract the atomic
mass from the
atomic number .
16
S
sulfur
32.064
2
8
6
AtomicMass 32
Atomic
Number16
16
Number of
protons
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To determine amount of electrons
6
C
CARBON
12.01115
2
4
To find the
number of
electrons in an
atom, look at the
numbers in the
right side. To
determine the
number of energy
levels count the
number of side
numbers and
there you go!!!
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33
AS
ARSENIC
74.9160
How to tell what period the
element is listed
2
8
18
5
4 ENERGY LEVELSAPPEARS IN THE4TH PERIOD
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What's the BIG difference
The big difference between an element,
compound, and a molecule is
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For instance . . .
This is an atom of an
element. As you can
see, it is made up of
only one kind of atom
. . In this case
HydrogenH
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Now, with a compound
H
O
O
When two or moreatoms are put
together it makes a
compound.
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Sulfur
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Vocabulary
! Electron! Neutron! Proton! Nucleus! Compound! Atom! Isotope! element
! Electronfields
! Mass! Atomic
structure
! Periodic table! Chemicalsymbol
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Suggested Vocabulary
! Element name! chemist! properties! matter! electron cloud! synthetic! metal! metalloid
! Solid! liquid! gas! noble gasses! subatomic! Nonmetals! particles
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! http://www.docstoc.com/docs/42433280/A-Brief-History-of-Atomic-
Theory
