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•C H E M I S T R Y H E L P C E N T E R
Review- Atomic Symbols & Isotopes
• ATOM SYMBOLS
mass number→A
atomic number→Z
X
• ISOTOPES: Have same # protons, different # neutrons
• REVIEW EXAMPLE
32
15
P
How many protons does an atom of
phosphorus-32 have?
 32
 30
 17
 15
32
15
P
How many electrons does an atom of
phosphorus-32 have?
 32
 30
 17
 15
32
15
P
How many neutrons does an atom of
phosphorus-32 have?
 32
 30
 17
 15
32
15
P
It’s Time For Some Donut Math!
 Dunkin Donuts sells both regular-sized donuts and
Munchkins
 Let’s say that of all the donuts sold:


78.3% are regular-sized (mass= 57g)
21.7% are Munchkins (mass= 10g)
 What is the weighted average mass of a Dunkin
Donut?
If Munchkins were more
abundant, would the average
mass of a Dunkin Donut go up
or down?
Isotopes and Average Atomic Mass
a
l
l
i
s
o
t
o
p
e
s
A
v
e
r
a
g
e
a
t
o
m
i
c
m
a
s
s
=
(
f
r
a
c
t
i
o
n
a
l
a
b
u
n
d
a
n
c
e
)

(
m
a
s
s
o
f
i
s
o
t
o
p
e
)

A Non-Edible Example
Silver has two isotopes:
Isotope
107
Ag
109
Ag
Mass (u)
% Abundance
106.905
51.839
108.905
48.161
What is the average atomic mass of Silver?
Mass Spectrometry Determines Mass:Charge
Mass spectrometry allows
us to determine the
natural abundances of the
different isotopes
What do these things have in common?
Floyd Landis Case
 Landis won 2006 Tour de France
 Tested positive for testosterone doping
 Question #1: Did Landis have an abnormally high
testosterone level?
testosterone
epitestosterone
Isotopes and Steroid Testing
 Question #2: Is the excess testosterone natural or
synthetic?
 Isotope-ratio mass spectrometry (CIR) used to determine
the ratio of 13C to 12C in Landis’ testosterone
 Photosynthesis prefers 12C

C3 plants: Strong preference for 12C

C4 plants: Less of a preference for 12C
 Normal diet= mixture of C3 and C4 plants
 Synthetic testosterone comes from soy, contains less 13C

13C:12C
reduced  Landis “tested positive” for doping
The Periodic Table
 Elements are arranged to highlight common
properties and trends
 Arrangement reflects microscopic structure of atom
The Periodic Table- Groups and Periods
Main Group & Transition Elements
Metals, Nonmetals, Metalloids
Groups with Names
Periodic Table