Download Atomic Theory

Chemical Foundations
Elements and Atoms
Why are elements important?
• Elements can be looked at like the
alphabet.
• Everything around us can be broken down
into smaller “building blocks.”
It’s all
about
building
blocks
Current View of Elements
• Currently there are 118 different
elements known.
• Only 88 of these are naturally occurring.
• Two new elements discovered recently.
– They were stable for only 1.2 sec.
Elements on Earth
Distribution (Mass Percent) of the 18 Most Abundant Elements in
the Earth’s Crust, Oceans, and Atmosphere
Element
Mass Percent
oxygen
silicon
aluminum
iron
calcium
sodium
potassium
magnesium
hydrogen
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 48
49.2
25.7
7.50
4.71
3.39
2.63
2.40
1.93
0.87
Element
titanium
chlorine
phosphorus
manganese
carbon
sulfur
barium
nitrogen
fluorine
all others
Mass Percent
0.58
0.19
0.11
0.09
0.08
0.06
0.04
0.03
0.03
0.49
Top Ten
Elements in the Human Body
Element
Six Million Dollar Man
Mass
Percent
Carbon: 18%
Calcium: 2%
Nitrogen: 3%
Hydrogen: 10%
Other elements: 2%
Oxygen: 65%
H
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Oxygen
Carbon
Hydrogen
Nitrogen
Calcium
Phosphorus
Magnesium
Potassium
Sulfur
Sodium
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 48
65.0
18.0
10.0
3.0
1.4
1.0
0.50
0.34
0.26
0.14
C N O
Ca
As a percentage of mass, humans
are made up of mostly nonmetals.
Names for the Elements
• Names of elements are based in
– Greek, Latin, German
– Gold called aurum, Latin for “shining dawn.”
– Lead was known as plumbum, which means
heavy.
– Chlorine and iodine comes from Greek words
describing their colors.
Elements in the Human Body
Carbon: 18%
Calcium: 2%
Nitrogen: 3%
Hydrogen: 10%
Other elements: 2%
Oxygen: 65%
H
C N O
Ca
As a percentage of mass, humans are made up of mostly nonmetals.
Symbols for Elements
• We use abbreviations to make our lives
easier.
• The symbols normally consist of the first
letter or first two letters or first letter and
next available letter of the element name.
– The first letter is always capitalized.
Examples
• Examples
Fluorine
Oxygen
Carbon
F
O
C
Neon
Silicon
Ne
Si
• Odd examples
Zinc
Chlorine
Zn
Cl
Cadmium
Platinum
Cd
Pt
The Names and Symbols of the Most Common Elements
Element
Aluminum
Antimony (stibium)*
Argon
Arsenic
Barium
Bismuth
Boron
Bromine
Cadmium
Calcium
Carbon
Chlorine
Chromium
Cobalt
Copper
Fluorine
Gold (aurum)
Helium
Hydrogen
Iodine
Iron (ferrum)
Lead (plumbum)
Symbol
Al
Sb
Ar
As
Ba
Bi
B
Br
Cd
Ca
C
Cl
Cr
Co
Cu
F
Au
He
H
I
Fe
Pb
Element
Lithium
Magnesium
Manganese
Mercury (hydrargyrum)
Neon
Nickel
Nitrogen
Oxygen
Phosphorus
Platinum
Potassium (kalium)
Radium
Silicon
Silver (argentum)
Sodium (natrum)
Strontium
Sulfur
Tin (stannum)
Titanium
Tungsten (wolfram)
Uranium
Zinc
Symbol
Li
Mg
Mn
Hg
Ne
Ni
N
O
P
Pt
K
Ra
Si
Ag
Na
Sr
S
Sn
Ti
W
U
Zn
*Where appropriate, the original name is shown in parentheses so that you can see the sources of some
of the symbols.
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 51
Cl2
a molecule of chlorine
e-
Cl1-
a chloride ion
Cl
an atom of chlorine
2Cl
NaCl
(an anion)
two atoms of chlorine
a compound of sodium chloride
A Collection of Argon Atoms
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 68
Nitrogen gas molecules
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 68
Oxygen gas molecules
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 68
Diatomic Molecules
Elements That Exist as Diatomic Molecules in Their Elemental Forms
Element Present
hydrogen
nitrogen
oxygen
fluorine
chlorine
bromine
iodine
Elemental State at 25 oC
colorless gas
colorless gas
pale blue gas
pale yellow gas
pale green gas
reddish-brown liquid
lustrous, dark purple solid
Molecule
H2
N2
O2
F2
Cl2
Br2
I2
Diatomic Elements, 1 and 7
H2
N2 O2 F2
Cl2
Br2
I2
Metals, Nonmetals, Metalloids
Metals and Nonmetals
1
2
3
H
He
1
2
Li
Be
B
C
3
4
5
Na Mg
11
4
K
19
5
7
Ca Sc
O
F
Ne
6
7
8
9
10
Al
Si
P
S
Cl
Ar
13
14
15
16
17
18
Ti
V
Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br
Kr
23
24
35
36
I
Xe
53
54
20
21
22
Rb Sr
Y
Zr Nb Mo Tc Ru Rh Pd Ag Cd
In
39
40
41
42
49
Hf
Ta
W
72
73
74
37
6
12
N
38
Cs Ba
55
56
Fr
Ra
87
88
*
W
Nonmetals
25
26
27
28
29
30
METALS
43
44
Re Os
75
76
47
45
46
Ir
Pt Au Hg
Tl
77
78
81
79
48
31
80
32
33
34
Sn Sb Te
50
51
Pb Bi
82
83
52
Po At Rn
84
85
86
Rf Db Sg Bh Hs Mt
104
105
106
107
108
Metalloids
109
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
57
58
59
Ac Th Pa
89
90
91
60
U
92
61
62
63
64
65
66
Np Pu Am Cm Bk Cf
93
94
95
96
97
98
67
68
69
70
71
Es Fm Md No Lr
99
100
101
102
103
Metals, Nonmetals, & Metalloids
1
Nonmetals
2
3
4
5
Metals
6
7
Metalloids
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 349
Periodic Table
The decomposition of two water
molecules.
Spherical atoms packed closely
together.
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 70
Pure water does not conduct an
electric current
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 75
Water containing dissolved salt
conducts a current.
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 75
Development of Atomic Theory
The Hellenic Market
Fire
~
Water
Earth
Air
Greek Model
“To understand the very large,
we must understand the very small.”
Democritus (400 B.C.)
• Greek philosopher – “thought”
experiments
• Idea of ‘atomos’
Atomos = ‘indivisible’
• Tear up a piece of matter until
you reach the atomos.
Democritus’s model of atom
”Nothing exists but atoms and space, all else is opinion”.
Alchemy
(500 – 1400 A.D.)
Alchemical symbols for substances…
..
.
......
.
.....
GOLD
SILVER
COPPER
IRON
SAND
transmutation: changing one substance into another
D
In ordinary chemistry, we cannot transmute elements.
Contributions
of alchemists:
Information about elements
- the elements mercury, sulfur, and antimony were discovered
- properties of some elements
Develop lab apparatus / procedures / experimental techniques
- alchemists learned how to prepare acids.
- developed several alloys
- new glassware
Dalton’s Atomic Theory 1805
Billiard Ball Model
1. All matter consists of tiny
particles called atoms.
2. Atoms cannot be subdivided,
created or destroyed.
3. All atoms of an element are
identical.
4. Atoms of different elements
are different from each other.
5. Atoms of different types
combine is specific ratios to
form compounds.
Radioactivity (1896)
Recall:Rays/Particles produced by unstable nuclei
a. Alpha Rays – helium nucleus
α-particle
b. Beta Part. – high speed electron
-particle
c. Gamma ray – high energy x-ray
-radiation (wave, no mass)
Antoine-Henri Becquerel
(1852 - 1908)
Thomson’s Experiment
1897
-
voltage
source
+
vacuum tube
metal disks
Thomson’s Experiment
-
voltage
source
+
vacuum tube
metal disks
Thomson’s Experiment
ON
-
OFF
voltage
source
+
Passing an electric current makes a beam appear
to move from the negative to the positive end
Thomson’s Experiment
ON
-
OFF
voltage
source
+
Thomson’s Experiment
ON
-
voltage
source
+
+
By adding an electric field…
he found that the moving pieces were negative.
Thomson’s Raisin Bun Model
1897
• Using cathode ray tubes, he
was able to deflect cathode
rays with an electric field.
• The rays are bent towards the
positive pole, indicating that
cathode ray particles are
negatively charged.
(electrons)
• Thomson’s model of the atom
was a + sphere with –
electrons embedded.
Thomson’s Plum-Pudding or
Raisin Bun Model
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 56
Ernest Rutherford (1871-1937)
Planetary Model of the Atom
• Learned physics in
J.J. Thomson’ lab.
• Noticed that ‘alpha’
particles were
sometime deflected
by something in the
air.
• Gold-foil experiment
Animation by Raymond Chang – All rights reserved.
Rutherford ‘Scattering’
• In 1909 Rutherford undertook a series of experiments
• He fired a (alpha) particles at a very thin sample of gold foil
• According to the Thomson model the a particles would only
be slightly deflected
• Rutherford discovered that they were deflected through large
angles and could even be reflected straight back to the source
Lead collimator
Gold foil
a particle
source
q
Rutherford’s Apparatus
Rutherford received the 1908 Nobel Prize in Chemistry for his pioneering work in nuclear chemistry.
beam of alpha particles
radioactive
substance
circular ZnS - coated
fluorescent screen
gold foil
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 120
Results of foil experiment if plumpudding had been correct.
Electrons scattered
throughout
-
+
-
positive
charges
+
+
+
+
-
-
+
+
+
-
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 57
-
Lead
block
Polonium
Florescent
Screen
Gold Foil
California WEB
What he expected…
California WEB
What he expected…
What he got…
richocheting
alpha particles
What he got…
richocheting
alpha particles
Rutherford’s
Gold Foil Experiment (1909)
Revised Theory
Interpreting the Observed
Deflections
deflected particle
.
.
.
.
.
.
beam of
alpha
particles
.
.
.
.
.
.
.
.
.
.
gold foil
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 120
.
undeflected
particles
Rutherford’s
Gold-Leaf
Experiment
Conclusions:
Atom is mostly empty space
Atom has a very small, dense,
positively charged core.
(nucleus)
Electrons float around nucleus
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 120
Evidence for Particles
In 1886, Goldstein, using equipment similar to cathode ray tube,
discovered particles with charge equal and opposite to that of
electron, but much larger mass.
Rutherford later (1911) found these particles to be identical to
hydrogen atoms minus one electron
- named these particles protons
Chadwick (1932) discovered particles with similar mass to proton
but zero charge.
- discovered neutrons
Discovery of the Neutron
9
4
Be
+
4
2
He
12
6
C
+
1
0
n
James Chadwick bombarded beryllium-9 with alpha particles,
carbon-12 atoms were formed, and neutrons were emitted.
Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 764
*Walter Boethe
An unsatisfactory model
for the hydrogen atom
According to classical physics, light
should be emitted as the electron
circles the nucleus. A loss of energy
would cause the electron to be drawn
closer to the nucleus and eventually
spiral into it.
Hill, Petrucci, General Chemistry An Integrated Approach 2nd Edition, page 294
Bohr’s Model
Nucleus
Electron
Orbit
Energy Levels
Quantum Mechanical Model
Niels Bohr &
Albert Einstein
Modern atomic theory describes the
electronic structure of the atom as the
probability of finding electrons within certain
regions of space (orbitals).
Modern View
• The atom is mostly empty space
• Two regions
– Nucleus
• protons and neutrons
– Electron cloud
• region where you might find an electron
Dalton (1803)
Thomson (1904)
(positive and negative charges)
+
+
+
+
+
Rutherford (1911)
(the nucleus)
+
..
.
. .
.. .
.
.
.
.
.
.
..
..
.
. .
.. .
.
. ... .
.
. . ..
. .
.
.. .
.
.. . .
.
..
Schrödinger (1926)
(electron cloud model – orbitals)
From the time of Dalton to Schrödinger, our model
of the atom has undergone many modifications.
Ralph A. Burns, Fundamentals of Chemistry 1999, page 137
. .
.
.. .
. . ..
Bohr (1913)
(energy levels - orbits)
. ...
...
..
.
..
.. .
.
. . . .
.
.. .
. . .. .
.
..
. .
.
.. .
.
.. . .
.
.
. .
.
.
.
..
.. ...
.
.
.. .
.
.. . .
. .
..
.
.
.
.
.
. .
. .
.
.
Dalton (1803)
Thomson (1904)
(positive and negative charges)
+
+
+
+
+
Rutherford (1911)
(the nucleus)
+
..
.
. .
.. .
.
.
.
.
.
.
..
..
Schrödinger (1926)
(electron cloud model – orbitals)
From the time of Dalton to Schrödinger, our model
of the atom has undergone many modifications.
Ralph A. Burns, Fundamentals of Chemistry 1999, page 137
.
. .
.. .
.
. ... .
.
. . ..
. .
.
.. .
.
.. . .
.
..
. .
.
.. .
. . ..
Bohr (1913)
(energy levels - orbits)
. ...
...
..
.
..
.. .
.
. . . .
.
.. .
. . .. .
.
..
. .
.
.. .
.
.. . .
.
.
. .
.
.
.
..
.. ...
.
.
.. .
.
.. . .
. .
..
.
.
.
.
.
. .
. .
.
.
Models of the Atom
Dalton’s
Greek model
model
(400
(1803)
B.C.)
Thomson’s plum-pudding
model (1897)
Bohr’s model
(1913)
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 125
Rutherford’s model
(1909)
Charge-cloud model
(present)
Models of the Atom
Dalton’s
model
Greek model
(1803)
(400 B.C.)
1803 John Dalton
pictures atoms as
tiny, indestructible
particles, with no
internal structure.
1800
Thomson’s plum-pudding
model (1897)
Rutherford’s model
(1909)
1897 J.J. Thomson, a British
1911 New Zealander
scientist, discovers the electron,
leading to his "plum-pudding"
model. He pictures electrons
embedded in a sphere of
positive electric charge.
Ernest Rutherford states
that an atom has a dense,
positively charged nucleus.
Electrons move randomly in
the space around the nucleus.
1805 ..................... 1895
1900
1905
1910
1904 Hantaro Nagaoka, a
Japanese physicist, suggests
that an atom has a central
nucleus. Electrons move in
orbits like the rings around Saturn.
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 125
1915
Bohr’s model
(1913)
1926 Erwin Schrödinger
1913 In Niels Bohr's
model, the electrons move
in spherical orbits at fixed
distances from the nucleus.
1920
1925
Charge-cloud model
(present)
1930
develops mathematical
equations to describe the
motion of electrons in
atoms. His work leads to
the electron cloud model.
1935
1940
1945
1924 Frenchman Louis
1932 James
de Broglie proposes that
moving particles like electrons
have some properties of waves.
Within a few years evidence is
collected to support his idea.
Chadwick, a British
physicist, confirms the
existence of neutrons,
which have no charge.
Atomic nuclei contain
neutrons and positively
charged protons.
Bohr Model
Neils Bohr
Planetary
model
After Rutherford’s discovery, Bohr
proposed that electrons travel in definite
orbits around the nucleus.
Particles in the Atom
Each element is chemically unique. To understand why they are unique,
you need to know the structure of the atom (the smallest particle of an element)
and the characteristics of its components.
Particles in the Atom
Atoms consist of electrons, protons, and neutrons.
1. Electrons and protons have electrical charges that are identical
in magnitude but opposite in sign. Relative charges of 1 and
+1 are assigned to the electron and proton, respectively.
2. Neutrons have approximately the same mass as protons but no
charge—they are electrically neutral.
3. The mass of a proton or a neutron is about 1836 times greater
than the mass of an electron. Protons and neutrons constitute
the bulk of the mass of the atom.
Copyright 2007 Pearson Benjamin Cummings. All rights reserved.
Subatomic particles
Name
Symbol
Relative
Charge mass
Actual
mass (g)
Electron
e-
-1
0
9.11 x 10-28
Proton
p+
+1
1
1.67 x 10-24
Neutron
no
0
1
1.67 x 10-24
Subatomic Particles
ATOM
NUCLEUS
ELECTRONS
PROTONS
NEUTRONS
Positive
Charge
Neutral
Charge
Negative Charge
equal in a
Atomic
Most Number
of the atom’s mass.
neutral atom
equals the # of...
QUARKS
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Subatomic Particles
• Quarks
– component of
protons &
neutrons
– 6 types
– 3 quarks =
1 proton or
1 neutron
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
He
Size of an atom
• Atoms are incredibly tiny.
• Measured in picometers (10-12 meters)
– Hydrogen atom, 32 pm radius
• Nucleus tiny compared to atom
– Radius of the nucleus near 10-15 m.
– Density near 1014 g/cm3
• IF the atom was the size of a stadium, the
nucleus would be the size of a marble.
California WEB
Counting the Pieces
C
12
C
6
14
6
Mass Number = A
Atomic Number = number of protons
# of protons determines kind of atom
C
12
6
Atomic Number = Z
Atomic Number = number of electrons in a neutral atom
Mass Number = the number of protons + neutrons
California WEB
Symbols
Contain the symbol of the element, the mass
number and the atomic number
# protons
+ # neutrons
mass number
# protons
Mass
number
Atomic
number
X
Symbols
• Find the
– number of protons = 9 +
– number of neutrons = 10
– number of electrons = 9
– Atomic number = 9
– Mass number = 19
19
9
F
Symbols
Find the
– number of protons = 35
– number of neutrons = 45
– number of electrons = 35
– Atomic number = 35
– Mass number = 80
http://www.chem.purdue.edu/gchelp/liquids/bromine.gif
80
35
Br
Symbols
Find the
– number of protons = 11
– number of neutrons = 12
– number of electrons = 11
– Atomic number = 11
– Mass number = 23
23
11
Na
Sodium atom
Symbols
If an element has an atomic number of
23 and a mass number of 51 what is
the
– number of protons = 23
– number of neutrons = 28
– number of electrons = 23
– Complete symbol
51
23
V
Symbols
If an element has 60 protons and 84
neutrons what is the
– Atomic number = 60
= 144
– Mass number
– number of electrons = 60
– Complete symbol
144
60
Nd
Symbols
If a neutral atom of an element has 78
electrons and 117 neutrons what is the
– Atomic number = 78
– Mass number = 195
– number of protons = 78
– Complete symbol
195
78
Pt
Atomic Structure
• ATOMS
– Differ by number of protons
• IONS
– Differ by number of electrons
• ISOTOPES
– Differ by number of neutrons
Masses of Atoms

Mass Number

Isotopes

Ions

Relative Atomic Mass

Average Atomic Mass
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Atomic #
Mass
p+
n0
e–
Ca
20
40
20
20
20
Ar
18
40
18
22
18
Br
35
80
35
45
35
20
18
35
Ca
Ar
Br
40.08
39.948
79.904
Bohr - Rutherford diagrams
• Putting all this together, we get B-R diagrams
• To draw them you must know the # of protons, neutrons,
and electrons (2,8,8,2 filling order)
• Draw protons (p+), (n0) in circle (i.e. “nucleus”)
• Draw electrons around in shells
He
p+
2
2 n0
Li
Li shorthand
p+
3
4 n0
3 p+
4 n0
Draw Be, B, Al and shorthand diagrams for O, Na
2e– 1e–
Be
B
Al
5 p+
6 n°
4 p+
5 n°
O
13 p+
14 n°
Na
8 p+
8 n°
2e– 6e–
11 p+
12 n°
2e– 8e– 1e–
Periodic Table
• Dmitri Mendeleev developed the
modern periodic table.
• Argued that element properties are
periodic functions of their atomic
weights.
• We now know that element
properties are periodic
functions of their
ATOMIC NUMBERS.
The Octet Rule
Atoms tend to gain, lose, or share electrons
until they have a full outer shell (either two or
eight valence electrons).
This fills the valence
shell and tends to give
the atom the stability
of the inert gasses.
8
ONLY s- and p-orbitals are valence electrons.
Stability
• Ion Formation
– Atoms gain or lose electrons to become more
stable.
– Isoelectronic with the Noble Gases.
1
2
3
4
5
6
7
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Electron Configurations
of First 18 Elements:
Hydrogen
1H
Helium
2He
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
3Li
4Be
5B
6C
7N
8O
9F
10Ne
Sodium
Magnesium
Aluminum
Silicon
Phosphorous
Sulfur
Chlorine
Argon
11Na
12Mg
13Al
14Si
15P
16S
17Cl
18Ar
Electron Dot Diagrams
Group
1A
1
2A
2
3A
13
4A
14
5A
15
6A
16
7A
17
H
8A18
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
Ga
Ge
As
Se
Br
Kr
s1
s2
s2p1
s2p2
s2p3
s2p4
= valence electron
s2p5
s2p6
Valence shell: Outer Level e-’s
• Valence electrons
• Usually involved in chemical
changes
• Dot diagram
–Symbol represents the nucleus
–Dots represent the outer e-’s
Formation of Cation
sodium atom
Na
sodium ion
Na+
ee-
e-
e-
e-
e-
ee-
e-
11p+
ee-
loss of
one valence
electron
e-
e-
11p+
e-
e-
e-
e-
e-
e-
e-
e-
Formation of Anion
chlorine atom
Cl
e-
egain of
one valence
electron
ee-
e-
e-
chloride ion
Cl1e-
eee-
e-
e-
e-
e-
ee-
e-
17p+
17p+
e-
e-
e-
e-
ee-
e-
e-
ee-
e-
e-
e-
e-
e-
ee-
e-
e-
Formation of Ionic Bond
chloride ion
Cl1-
sodium ion
Na+
e-
e-
ee-
e-
e-
e-
e-
e-
e-
e-
e-
11p+
e-
e-
e-
e-
e-
e-
17p+
e-
e-
e-
e-
e-
e-
ee-
e-
e-
Ionic Bonding
NaCl
n=3
-
n=2
n=3
-
-
-
-
-
-
-
Na
[Ne]3s1
-
-
-
+
-
-
-
-
-
-
-
-
-
Cl
[Ne]3s23p5
-
-
-
Na+
[Ne]
-
-
-
Cl[Ne]3s23p6
Transfer of electrons to achieve a stable octet (8 electrons in valence shell).
Covalent Bonding
n=2
-
-
-
-
n=1
-
-
-
-
+
-
-
-
-
-
-
-
-
-
-
-
-
-
O
[He]2s22p4
-
O
[He]2s22p4
O2
Sharing of electrons to achieve a stable octet (8 electrons in valence shell).
Half-Life of Isotopes
Half-Lives and Radiation of Some Naturally Occurring Radioisotopes
Isotope
Half-Life
Radiation emitted
Carbon-14
5.73 x 103 years

Potassium-40
1.25 x 109 years
, 
Radon-222
3.8 days
a
Radium-226
1.6 x 103 years
a, 
Thorium-230
7.54 x 104 years
a, 
Thorium-234
24.1 days
, 
Uranium-235
7.0 x 108 years
a, 
Uranium-238
4.46 x 109 years
a
Mass Number
• mass # = protons + neutrons
• always a whole number
Neutron
+
• NOT on the
Periodic Table!
Electrons
Nucleus
e-
+
e-
e-
+
+
+
+
Nucleus
e-
ee-
Carbon-12
Neutrons 6
Protons
6
Electrons 6
Proton
Isotopes
• Atoms of the same element with different
mass numbers.
• Nuclear symbol:
Mass #
12
Atomic #
6
• Hyphen notation: carbon-12
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
C
Isotopes
Neutron
+
Electrons
Nucleus
+
+
+
+
+
Nucleus
Proton
Proton
Nucleus
Carbon-12
Neutrons 6
Protons
6
Electrons 6
+
+
+
+
Neutron
Electrons
+
+
Carbon-14
Neutrons 8
Protons
6
Electrons 6
Nucleus
6Li
7Li
3 p+
3 n0
3 p+
4 n0
2e– 1e–
2e– 1e–
Neutron
Neutron
Electrons
Electrons
+
Nucleus
+
+
Nucleus
+
Nucleus
Lithium-6
Neutrons 3
Protons
3
Electrons 3
Proton
+
+
Nucleus
Lithium-7
Neutrons 4
Protons
3
Electrons 3
Proton
17
Cl
Isotopes
37
• Chlorine-37
– atomic #:
17
– mass #:
37
– # of protons:
17
– # of electrons: 17
– # of neutrons: 20
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
37
17
Cl
Isotopes of Magnesium
12e-
12e12p+
12n0
Atomic symbol
24
12
Mg
12p+
13n0
25
12
Mg
12e12p+
14n0
26
12
Mg
Number of protons
12
12
12
Number of electrons
12
12
12
Mass number
24
25
26
Number of neutrons
12
13
14
Mg-24
Mg-25
Mg-26
Isotope Notation
Timberlake, Chemistry 7th Edition, page 64
Isotopes of Hydrogen
Protium
1
p+
Deuterium
1 e-
1
H
1
(ordinary hydrogen)
H-1
Ralph A. Burns, Fundamentals of Chemistry 1999, page 100
1 p+
1n
2
H
1
(heavy hydrogen)
H-2
Tritium
1 e-
1 p+
2n
3
1
1 e-
H
(radioactive hydrogen)
H-3
Isotopes of Hydrogen
• Protium (H-1)
1 proton, 0 neutrons, 1 electron
most abundant isotope
1 p+
1 e-
1 p+
1n
1 e-
1 p+
2n
1 e-
• Deuterium (H-2)
1 proton, 1 neutron, 1 electron
used in “heavy water”
• Tritium (H-3)
1 proton, 2 neutrons, 1 electron
radioactive
Isotopes of Three Common Elements
Mass
Element
Carbon
Chlorine
Silicon
Symbol
Mass (amu)
Fractional
Abundance
Number
12
6
C
12
12 (exactly)
99.89%
13
6
C
13
13.003
1.11%
35
17
Cl
35
34.969
75.53%
37
17
Cl
37
36.966
24.47%
28
29
30
27.977
28.976
29.974
28
14
29
14
Si
Si
30
Si
14
LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 110
92.21%
4.70%
3.09%
Average
Atomic
Mass
12.01
35.45
28.09
Radioisotopes
• Radioactive isotopes
• Many uses
– Medical diagnostics
– Optimal composition of
fertilizers
– Abrasion studies in engines and
tires
– Finding the age of fossils and
ancient artifacts
Radioisotope is injected
into the bloodstream to
observe circulation.
Review - Development of Atom Model
e
e
+
e
e
+
+
e
+e
+e
e
+ e + e
Dalton’s
model
Greek model
(1803)
(400 B.C.)
-
+
Thomson’s plum-pudding
model (1897)
-
- +
Rutherford’s model
(1909)
Bohr’s model
(1913)
Charge-cloud model
(present)
Neils Bohr
•planetary model of atom
•electrons in fixed "orbit"
•energy level = ring on atom
J.J. Thomson
Democratus (Greek)
•cathode ray tube experiment
•bowling ball
•discovered electrons and protons
•no experiments
_
•mental model
•term "atomos" = indivisible
Ernest Rutherford
•discontinuos theory of matter
•gold foil experiment
+
•atom mostly empty space
•nucleus (small & (+) charge)
William Thomson (Lord Kelvin)
•alpha particles (+) charged
•proposed "plum-pudding" model
•Geiger counter to detect radiation
•ZnS coated screen
John Dalton
•bowling ball
•based on experimental evidence
•law of conservation of mass - Lavoisier
•law of definite proportions - Proust
•law of multiple proportions
•NO protons, NO electrons, NO neutrons
•Atom should collapse
Quantum-Mechanical Model
Developed by many scientists:
Albert Einstein
Erwin Schrodinger (math)
Louis DeBroglie (wave nature)
Werner Heisenberg (probability)
Max Planck (quanta)
•s, p, d, f-orbitals
•based on probability
•Heisenberg Uncertainty principle
•quantum mechanics (math)