Chapter 3 – Atomic Structure
Development of the Atomic Theory
Democtritus
• Greek
• First coined the term
“Atom” which means
invisible and indivisible.
• Came up with the theory
while trying to starve
himself to death.
• Aristotle had opposing
theory which was
believed for 2000 years
Boyle & Newton
Robert Boyle
• Began ‘experimental
chemistry’
• Studied gases
• Worked with Newton to
bring alchemy out of the
“dark ages” . Eventually
became Chemistry.
Isaac Newton
• Isaac Newton was one of
the first people to propose a
“mechanical universe.” He
believed that the universe is
made up of small solid
masses that are constantly
in motion. This idea is
known as “The Mechanical
Universe” idea.
• Wrote article “Skeptycal
Chemyst”
John Dalton
• John Dalton formulated the Atomic Theory which
states that:
• atoms cannot be divided or separated
• atoms of one element are the same
• atoms of an element are different than atoms of other
elements
• atoms of different elements can be combined in
whole number ratios to form compounds
• Used actual experimental work from Antoine
Lavoisier (Law of conservation of Mass) and
Joseph Proust (Law of Definite Proportions) to
support his theory.
Atomic Mass
• The atomic mass on the Periodic Table of
Elements is a WEIGHTED AVERAGE.
• Measured in atomic mass units (amu)
• The amu is based on 1/12 the mass of a
carbon-12 atom
• 1 amu = 1.66 x 10-27 kg
The Mole
• SI unit for amount of a substance is the mole
• 1 mole = 6.02 x 1023 particles
– A particle can be an atom, ion, molecule,
compound or formula unit
• This is called Avogadro’s Constant
• 1 mole of a substance = mass of substance
from PTE in grams
• 6.02 x 1023 particles of a substance = mass of
substance from PTE in grams
Modern Atomic Structure
JJ Thomson
• Experimented with Cathode rays.
• Based on the work that he did, he discovered
electrons, the first subatomic particle
• He also developed a model of the atom called the
“plum pudding” model.
•Because of Thomson’s work, Dalton’s
theory was adjusted.
http://www.youtube.com/watch?v=RW_zfKOU9uM
Rutherford
• Student of Thomson.
• Designed gold Foil Experiment to prove
Thomson’s model.
• His experiment disproved Thomson and he
proposed his own theory, the nuclear model
of the atom. http://www.youtube.com/watch?v=bSEOOMs5VNU
Modern Atomic Structure
• Scientists now know that there are three
major subatomic particles: protons, neutrons
and electrons.
Particle
proton
neutron
electron
Location
Mass
nucleus
1 amu
nucleus
1 amu
orbit nucleus 1/2000
(in the
amu
electron cloud)
Charge
+
none
-
How does this relate to the PTE?
• You can use the periodic table of elements
(PTE) to figure out how many protons,
neutrons and electrons are in any atom on the
table.
Atomic mass (A) = p
+ n in the nucleus
Atomic number (Z) =
number of protons in
the nucleus
Au
197
79
Neutrons can be
found by subtracting
the atomic mass from
the atomic number:
N=A-Z
Atoms, Ions and Isotopes
• The number of protons in an atom NEVER
changes. This is how you identify an element. If
the number of protons are changed, you have a
whole new element. Atoms are electrically
neutral (protons = electrons).
• If an atom is heavier/lighter than expected
(greater or lower atomic mass than on the PTE),
neutrons have been added or lost. This is now an
isotope.
• If an atom becomes charged, it has lost (+) or
gained (-) electrons. It is now an ion.
Name
Symbol
uranium
A
Z
92
P
N
E
148
50
46
85
+1
Rb
37
59
28 Ni
48
62
46
Atom, Ion or
Isotope?
Name
Symbol
A
Z
P
carbon
N
8
54
33
gold
E
54
40
28
207
43
19
18
Atom, Ion or
Isotope?
ELEMENT
SYM
A
Z
P
N
13
79
14
114
17
197
7
240
88
48
18
80
2
17
3
83
92
74
58
38
24
19
E
130
36
25
20
51
54
ATOM, ION
OR ISOTOPE
ELEMENT
Aluminum
Gold
Cadmium
Chlorine
Mercury
Lithium
Bismuth
Uranium
Tungsten
Cerium
Strontium
Chromium
Potassium
Antimony
SYM
A
Z
P
N
E
Al
197
79 Au
114
48 Cd
36
-1
17 Cl
197
80 Hg
7
+1
3 Li
213
83 Bi
240
92 U
184
74 W
140
58 Ce
88
+2
38Sr
49
24 Cr
39
19 K
122
-3
51 Sb
27
197
114
36
197
7
213
240
184
140
88
49
39
122
13
79
48
17
80
3
83
92
74
58
38
24
19
51
13
79
48
17
80
3
83
92
74
58
38
24
19
51
14
118
66
19
117
4
130
148
110
82
50
25
20
71
13
79
48
18
80
2
83
92
74
58
36
24
19
54
27
13
ATOM, ION
OR ISOTOPE
Atom
Atom
Isotope
Ion
Isotope
Ion
Isotope
Isotope
Atom
Atom
Ion
Isotope
Atom
ion