Chemistry
Section
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Name:
ISOTOPE WS KEY
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Date:
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Define the following terms.
1. atomic number (Z): The number of protons in the nucleus.
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2. mass number: The number of protons and neutrons in the nucleus.
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3. isotope: Atoms of the same element (same number of protons) having differing numbers of
neutrons.
4. nuclide: Atoms of a given element which have the same number of neutrons.
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Answer the following questions.
5. What is the result if the atomic number of a nuclide is subtracted from the mass number of
that nuclide?
The number of neutrons.
Look at Table 4.3 on the top of page 114. Write the symbol for each of the following:
6. proton p or p+
7. neutron n or n0
8. electron e–
In the third paragraph of page 117, find the name of the method used to describe an isotope
when written as copper-63:
9. isotope notation (or hyphen notation)
Write the nuclear symbol method for showing copper-63 that shows the chemical symbol,
mass number, and atomic number as shown in figure 4-16 at the top of page 117.
10.
Cu
The superscript in the symbol
14
6
C represents the
11. mass number
while the subscript in the symbol
14
6
C represents the
12. atomic number
Because the atomic number for any given element is always the same, the atomic number is
often not written for a specific nuclide of that element. The atomic number can be found
on any Periodic Table (like the one on page 9 of your reference tables). In other words,
12
6
C
is often written simply as
12
C
For each of the following nuclides, find the number of protons, neutrons, and electrons you
would expect to find in a neutral atom. The first one has been done for you.
1H
p+ = 1
n0 = 0
e– = 1
2H
p+ = 1
n0 = 0
e– = 1
3H
p+ = 1
n0 = 0
e– = 1
3He
p+ = 1
n0 = 0
e– = 1
9B
p+ = 5
n0 = 4
e– = 5
10B
p+ = 5
n0 = 5
e– = 5
14C
p+ = 6
n0 = 8
e– = 6
14N
p+ = 7
n0 = 7
e– = 7
40K
p+ = 19
n0 = 21
e– = 19
48Ca
p+ = 20
n0 = 28
e– = 20
13. How many protons, neutrons and electrons are in an atom of chlorine-37?
p+ = 17, n0 = 20, e– = 17
14. Write the nuclear symbol for an atom of boron-11.
Last printed 10/15/2014 6:30:00 AM
15. Write the hyphen notation for the neutral atom of an element that contains 8 electrons and
10 neutrons.
oxygen-10
16. The atomic mass unit, amu, is based on which nuclide?
carbon-12
Copper is element number 29. Find the averaged atomic mass of copper on the Periodic Table
on page 9 of your reference tables then write that mass in the space below.
17. 63.546 u
If atomic mass is based on
12
6
C having a mass of exactly 12 amu, you may be wondering why
there are decimals in the averaged masses of the elements. That is because the masses
shown on your tables are the weighted average of all the naturally occurring isotopes. Here
is an example of how to calculate these averages for the two naturally occurring isotopes of
copper.
63
Cu has a mass of 62.929 599 amu and occurs 69.17% of the time
65
Cu has a mass of 64.927 793 amu with a natural abundance of 30.83%.
First, convert the percentages to their decimal equivalents: 69.17% = 0.6917 and 30.83% =
0.3083. Now calculate the weighted averages of each nuclide and sum them together.
+
63
Cu : 0.6917 x 62.929 599 amu
65
Cu : 0.3083 x 64.927 793 amu
Cu = 63.55 amu
Now it’s your turn. Begin the practice problems 18 – 24 from page 121 in your book.
Answers to these questions are in the Teacher’s Edition of the text.
Last printed 10/15/2014 6:30:00 AM