Isotopes
atoms of a given element that
differ in the number of neutrons
…and consequently in mass.

Definition of Isotopes
Isotopes are atoms of the same
element which contains the same
number of protons but different
number of neutrons.

Isotopes
16
8
mass
number
proton
number
OO O
Oxygen-16
n = 8
Oxygen-17 Oxygen-18
17 18
8 8
n = 17 – 8
= 9
n = 18 – 8
= 10

Isotopes
Isotopes have the same chemical
properties but slightly different
physical properties

element have the
Q. Do all isotopes of the same
same mass?

Working with Atomic Notation
A
zX
Atomic Number
Chemical Symbol
Atomic Mass
(of Isotope)

Example #1
12
6C
Atomic Number
Chemical Symbol
Atomic Mass
(of Isotope)

Example #2
13
6C
Atomic Number
Chemical Symbol
Atomic Mass
(of Isotope)

Example #3
14
6C
Atomic Number
Chemical Symbol
Atomic Mass
(of Isotope)

Some isotopes of carbon
12
6C 13
6C 14
6C

Isotopes of Some Elements and Their
Atomic Mass

10
Ne
Neon
20.1797
3
Li
Lithium
6.941
47
Ag
Silver
107.8682
11
Na
Sodium
22.98977

Various ways of identifying
Isotopes
• Using atomic notation,
Example: 12
6 C or simply 12 C
•Using the mass notation.
Example: Carbon-12 or C-12
(read “carbon twelve” or “C twelve”)

Some Isotopes of Carbon
mass
notation
atomic
notation
# of p+ # of e- # of no
C-11 11C 6 6
C-12 12C 6 6
C-13 13C 6 6
C-14 14C 6 6

Another example of isotopes
1
1H 2
1H 3
1H
or
H-1 H-2 H-3

The Isotopes of Hydrogen
mass
notation
atomic
notation
# of p+ # of e- # of no
Hydrogen-1 1H 1 1
Hydrogen-2 2H 1 1
Hydrogen-3 3H 1 1

p+ =
no =
e- =
p+ =
no =
e- =
p+ =
no =
e- =
Figure #1 Figure #2 Figure #3

Isotopes
atoms of a given element that
differ in the number of neutrons
…and consequently in mass.

Keep in mind:
It is not possible to determine how many
different isotopes exist by looking at the
periodic table.
It is not possible to determine the
frequency of various nuclides by looking
at the periodic table.

(parenthesis) on the
Periodic Table indicate the
most stable isotope
stable means “longest living”
Parenthesis also suggest the element of
interest is radioactive.

Review problem #1
Represent the following using atomic notation.
92
U
Uranium
238.0289

Review problem #2
Represent the following using mass notation.
10
Ne
Neon
20.1797

Review problem #4
How many total subatomic particles are in the following
“neutral” atoms of Fe-55 and Fe-57?

RADIO ISOTOPES
Parent isotope
Radioactive decay
heat
Daughter isotope

Stable vs. Unstable
• A stable isotope does NOT undergo
radioactive (or nuclear) decay.
• An unstable isotope undergoes
radioactive (or nuclear) decay.
Unstable isotopes are also known
as radioisotopes or radionucleides

Stable vs. Unstable
• Stable isotopes:
• They do not naturally decay but exist in
natural materials in differing
proportions.
• Unstable isotope
• Isotopes that continuously break down
into lower atomic weight isotopes.

Uses of Radioactive Isotopes
• Food irradiation
• Archaeological dating (carbon-
dating)
• Smoke detectors
• Radioactive tracers

Isotope
Assessment of Learning

Represent the following using ATOMIC NOTATION
17
Cl
Chlorine
37.65
8
O
Oxygen
17.999
92
U
Uranium
235.0289
6
C
Caarbon
14.011
9
F
Flourine
14.998

Represent the following using MASS NOTATION
27
Co
Cobalt
60.998
33
As
Arsenic
72.922
92
U
Uranium
235.0289
53
I
Iodine
131.404
11
Na
Sodium
24.989

The Isotopes
How many total subatomic particles are in the following:
Complete the table.
mass
notation
atomic
notation
# of p+ # of e- # of no
Lead-208 82
199Au
Bismuth-211 83

The Isotopes
How many total subatomic particles are in the following:
Complete the table.
mass
notation
atomic
notation
# of p+ # of e- # of no
Lead-208 208Pb 82 82 126
Gold-199 199Au 79 79 120
Bismuth-211 211Bi 83 83 128