CHEMISTRY
OCTOBER 30, 2014
LAB 05 - ISOTOPES
LAB STARTER
• You have 2 minutes. You
are seated and quiet
• Read the Pre-Lab and
answer the question
AIM
• How does the average
atomic mass provide us
details about the
properties of the element?
ISOTOPES
• Atoms of the same atomic number but
different masses
– Due to different numbers of neutrons
ATOMIC MASS
• Also known as the average atomic mass
• Also known as the weighted average atomic
mass
– Take into account both the mass and the relative
abundance
EXAMPLE
• CANDY STORE(CANDIUM)
– 3 TYPES OF CANDIES (ISOTOPES)
• M&M
• Skittles
• Reese’s
RELATIVE ABUNDANCE
• For each types of candies (isotope), need to
know
– Count: how many of each types of candies
(Isotope)
– Total Count: total number of candies
(isotope) in the candy store
– Relative abundance: Percent each type of
candies (isotope) represents of the total.
For example, M&M group represent how
much of the total group of candies
AVERAGE MASS
• Weigh each type of candies (isotope)
• Average Mass per candy (isotope)
– Take the mass for each type of candies(isotope)
and divide by the number of candies in each type.
• Ex: instead of weighing each M&M, you weigh the
entire group of M&Ms and then you divide the entire
mass of the M&Ms by the number of M&Ms to find out
how much each M&M approximately weigh (average
mass of each M&M)
RELATIVE MASS
• TAKE THE RELATIVE ABUNDANCE BY THE
AVERAGE MASS OF EACH ISOTOPE TO GET THE
RELATIVE ABUNDANCE
– So take the average mass for each type and
multiply by the relative abundance for each type
• EXAMPLE: for each type of candies, find out how much
of the entire mass does each type of animals represent
– So M&Ms represent how much of the entire candy mass
WEIGHTED AVERAGE MASS
• ADD THE RELATIVE MASS OF EACH TYPE OF
ISOTOPES TO GET THE ATOMIC MASS
– Add the relative mass of M&M + Skittles + Reese’s
POST LAB QUESTIONS 1-2
• TAKE 1 MINUTE TO ANSWER QUESTIONS 1
AND 2. YOU MAY CONSULT WITH YOUR
PARTNER BUT YOUR ANSWER IS YOUR OWN
POST LAB QUESTION 3
• TURN TO THE NEXT GROUP AND OBTAIN
THEIR AVERAGE ATOMIC MASS (ANSWER TO
#6 ON PAGE 3).
• Write it down and then respond to question 3.
• You have 3 minutes to do question 3
• You may consult with your partner but the
writing is your own.
POST LAB QUESTION 4
• LET’S REVISIT THE AIM:
– How does knowing the atomic mass provide us
with details about the properties of an element?
– Take 3 minutes to respond to the question