Download Atomic Structure

Development of the
ATOMIC THEORY
Early Studies of Matter
 The
Greeks – more than 2000 years ago
– Four Elemental Substances:
 Fire,
Earth, Wind, and Water
Democritus – 460 BC
 Proposed
that all matter is made up
of indivisible particles that he called
 Aristotle
disagreed…so Democritus’
theory remain dormant until Dalton.
Democritus vs. Aristotle
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Robert Boyle - 1661
 Proposed
that matter
is composed of
simple substances
called elements that
cannot be further
decomposed or
broken down.
Antoine Lavoiser - 1772
 Importance of
 First stated
Conservation of Mass
H2 (g) + O2 (g)  H2O (l)
20 g + 160 g

180 g
Mass is neither created nor destroyed!
J. Proust – 1799

In a pure compound,
the elements combine
in definite proportions
to each other.
Law of Definite Proportions
decomposes
H2O (l)

450 g 
90 g 
H2 (g) + O2 (g)
50 g + 400 g
10 g + 80 g
When water decomposes the ratio of the
mass of O2 to H2 is always 8:1
Law of Multiple Proportions
 Two
elements can combine to form
more than one compound
C + O  CO
1.00 g + 1.33 g  2.33 g
`
C + O +O  CO2
1.00 g + 2.66 g  3.66 g
 Ratio
of the masses always a whole
number!
John Dalton & Atomic Theory
1803
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Dalton’s Atomic Theory


Matter is composed of very small particles
called atoms.
Atoms are indivisible and cannot be
created or destroyed.*

All atoms of a given element are identical.*

Atoms of different elements are different.


Different atoms combine in whole
number ratios to form compounds.
In chemical reactions, atoms are combined,
separated or rearranged.
Dalton’s Model of the Atom
 Solid,
indivisible sphere
 Analogy:
BILLARD BALL
So Dalton’s atoms are kind of like
billiard balls.
Atoms combine
in whole-number
ratios.
In a reaction, atoms are
rearranged.
+

+
+
So how big is an atom?

Most atoms are 1-2
angstroms across.
– An angstrom =
1 X 10-10 m.

6 Billion Copper
atoms in a line less than 1 meter!