Transcript ISOTOPES - Wayzata Public Schools

Isotopes & Average Atomic
Mass
What are isotopes?
Atoms of the
same element
that have
different
numbers of
neutrons and
different
atomic masses.
Are these isotopes?
85%
1.
2.
Yes
No
15%
1
2
The average atomic mass of
Carbon is 12.011 amu. Which
isotope of Carbon would you
expect to find in nature the
majority of the time?
1.
2.
3.
4.
Carbon - 12
Carbon - 13
Carbon - 14
They are all
equally found in
nature
70%
11%
1
2
7%
3
11%
4
Weighted Averages
Ages:
Find average age:
What is average atomic mass?
► The mass calculated when we take into account
all of the isotopes that exist and the abundance
(percentage) of each type.
Chlorine 35
Abundance = 75.77%
Chlorine 37
Abundance = 24.23%
How to calculate
Example:
Step #1
Chlorine
75.77% - Cl 35
24.23% - Cl 37
Isotope
Number
of
Protons
Number
of
Neutrons
Cl – 35
Cl - 37
Step #2
Predict: Average atomic mass based on masses and percentages:
amu
Step #3
Calculate average mass:
(mass x percent) + (mass x percent) + . . .
= average atomic
mass
(35 x 0.7577) + (37 x 0.2423) = 35.5 amu
1.
2.
3.
4.
5.
6.
7.
What is different between
isotopes of the same element?
Atomic # only
Mass # only
# of protons only
# of neutrons only
Both atomic # and
# of protons
Both mass # and #
of neutrons
Both # of neutrons
and # of protons
81%
11%
4%
0%
0%
1
2
4%
0%
3
4
5
6
7
M&M lab