Transcript Isotopes and Mass Number

Isotopes and
Mass Number
Isotope
Atoms of the same element with:
Same number of protons
BUT
Different number of neutrons
ELEMENT IS TO ISOTOPE AS DOG IS TO DOG BREED
Mass Number: Mass of an atom

FLASHBACK:






Protons are what animal?
Neutrons are what animal?
Electrons are what animal?
Mass # = mass of the nucleus
Nucleus = protons + neutrons
Therefore:
mass# = protons + neutrons
Nomenclature
Carbon - 14
Mass Number
14
6
Atomic Number
C
Practice
1.
Carbon – 12
12
6
6
C
Oxygen - 17
2.
17
8
9
O
Draw Diagram
p+
en0
6
Mass #
12
p+
8
e-
8
n0
9
Mass #
17
6
6
Calculating Atomic Mass
Atomic Mass is the average of all an
element’s masses
 You need two values

Mass of each isotope
 % abundance of each isotope


Percent abundance is how much of the isotope is represented
in the world
Example: The following is data for
the unknown element X.
For element 6 X
mass = 6.015
abundance = 7.50%
For element 7 X
mass = 7.016
abundance = 92.5%
Atomic Mass Chart
Isotope
Mass
(amu)
%
Abundance
X-6
6.015 x 7.50
45.1
X-7
7.016 x 92.5
649
+
694
100
=
6.94 amu
Find the atomic
mass on the
periodic table
What is element
6.94
amu
X?
The element is Lithium!