Name: _________________
Period: _____
Date: _____________
Isotopes, Natural Mixtures & Mass Spectrometry
Review: Fill in the table
Atomic
Element
Number, Z
Mass
Number, A
Number of
Protons
Number of
Neutrons
Number of
electrons
Cm
96
247
96
151
96
P3-
15
31
15
16
18
Fe2+
26
56
26
30
24
Isotopes
Isotopes are ___________________________________________________________
Compare three isotopes of carbon:
6
6
C
6
C
12
C
13
14
carbon-12
carbon-13
carbon-14
p+ =
p+ =
p+ =
n=
n=
n=
Isotopes of the same element have:
•
the same number of protons and electrons
•
different number of neutrons
•
different mass
Examples: Calculate the number of neutrons in the following isotopes
mass = 15 neutrons = 15 – 7 = 8
Nitrogen-15
atomic number = 7
Calcium-45
atomic number = 20 mass = 45 neutrons = 45 – 20 = 25
Iodine-131
atomic number = 53 mass = 131 neutrons = 131 – 53 = 77
Name: _________________
Period: _____
Date: _____________
Natural Mixtures of Isotopes
Most elements exist as _______________________________. Since samples of
elements consist of a mixture of isotopes, __________________________________
________________________________________.
Percent (%) abundance: ____________________________________
Example: Isotopes of Chlorine
17
75.77% of all chlorine atoms are chlorine-35
24.23% of all chlorine atoms are chlorine-37
Cl
35.5
Calculating the relative atomic mass (Ar) of samples containing a mixture of
isotopes:
average atomic mass = (%1)(m1) + (%2)(m2) + …. (%n)(mn)
NOT: (m1 + m2 + ….)/ n
Example: Calculate the relative atomic mass of chlorine if
35Cl
= 75.77%, 37Cl = 24.23%
Average mass = 0.7577 x 35 + 0.2423 x 37 = 35.5 g
Activity: Calculate the relative atomic mass of Jellybeanium using the data below and
your sample of Jellybeanium
Isotope
Colour
Number in bag
% Abundance
Jb-42
Red
22
68.75
Jb-43
Green
7
21.875
Jb-44
White
3
9.375
atomic mass = (0.6875 x 42) + (0.21875 x 43) + (0.09375 x 44) =
Name: _________________
Period: _____
Date: _____________
Mass Spectrometry
A mass spectrometer is an instrument used by scientists to determine the relative
atomic mass of a sample of isotopes. Mass spectrometers work by separating atoms of
different masses using magnetic field.
Example: Deduce the relative atomic mass of the element
rubidium from the data given in the mass spectrum.
90
77
80
1. Assume sample has 100 atoms
2. Total mass of 100 atoms = (85*77) + (87*23) = 8546
3. Relative atomice mass = average mass of atom
= total mass/number of atoms = 8546/100 = 86.46
% abundance
70
60
50
40
30
23
20
10
0
84
85
86
87
mass/charge
Example: Helium exists in two isotopic forms, 10B and 11B.
Use your periodic table to find the abundances of the two
isotopes. Draw the mass spectrum helium.
100
90
% abundance
80
70
60
50
40
30
20
10
0
mass/charge
88