Reconstructing Atomic Theory | STUDENT GUIDE
2
S-8
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Name
Date
Activity 2. Atomic Number, Atomic Mass, and
Mass Number
MATERIALS
Periodic Table of
the Elements
With your partner, answer the questions that follow.
Compare the three atoms, and then fill in the chart below.
Atom 1
Atom 2
Key
* = protons
= electrons
= neutrons
Atom 3
Atom 1
Atom 2
Atom 3
Number of electrons
Number of protons
Number of Neutrons
1. What structural characteristic do all these atoms share?
2. Do the atoms shown above depict the same element? How do
you know they do or do not?
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Atom 1 is the most common form, or isotope, of lithium; Atom 2 is a
stable but less abundant isotope of lithium, and Atom 3 is a lithium
ion. Look at the following three notations for lithium.
7
3 Li
6
3 Li
7 +1
3 Li
©2009 Carolina Biological Supply Company
Reconstructing Atomic Theory | STUDENT GUIDE
2
S-9
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Name
Date
Activity 2. (continued)
A
ZX
X = chemical symbol of the element
Z = atomic number
A = mass number
3. What is different between the two isotopes of lithium?
4. What is different between the isotopes and the ion?
5. What subparticle is represented by the atomic number?
6. What subparticle identifies the atom?
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7. Why doesn’t the number of neutrons identify an element?
©2009 Carolina Biological Supply Company
Reconstructing Atomic Theory | STUDENT GUIDE
2
S-10
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Date
Activity 2. (continued)
8. Why doesn’t the number of electrons identify an element?
9. What does the mass number represent?
10. Why is the mass number different between the two isotopes?
11. Why is the mass number of the ion the same as the mass
number of the isotopes?
12. Why does the ion have a +1 charge?
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©2009 Carolina Biological Supply Company
Reconstructing Atomic Theory | STUDENT GUIDE
2
S-11
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Date
Activity 2. (continued)
13. Can a chemical change alter the identity of an atom, i.e.,
change its atomic number?
Look at the following representation of lithium.
3
Li
Lithium
6.941
[He]2s1
atomic number
symbol
name
average atomic mass
electron configuration
14. What does average atomic mass represent?
15. How is average atomic mass different from mass number?
16. Can you determine the number of neutrons in the nucleus of an
atom by looking at the element’s average atomic mass and the
atomic number? Why or why not?
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©2009 Carolina Biological Supply Company
Reconstructing Atomic Theory | STUDENT GUIDE
3
S-12
Explain
Name
Date
Activity 2. Atomic Number, Atomic Mass, and
Mass Number
For questions 1 and 2, look at the diagrams below, and then write
A
the Z X notation on the line below the diagram. Use the periodic
table to identify each element.
A
ZX
Key
X = chemical symbol of the element
Z = atomic number
A = mass number
electrons
* == protons
= neutrons
1. ___________________ ___________________
___________________
2. ___________________ ___________________
___________________
3. Look at the notation below each box, and then draw the
corresponding atom in the box. Use the periodic table to
identify each element.
12
6C
13
6C
14
6C
©2009 Carolina Biological Supply Company
Reconstructing Atomic Theory | STUDENT GUIDE
3
S-13
Explain
Name
Date
Look at the diagrams below:
Key
electrons
* == protons
= neutrons
4. Are these diagrams of the same atom? How do you know?
5. Fill in all the information missing in the chart below using the
periodic table to determine the element.
Hint: Only the last atom in the chart is an ion.
Symbol
Number of
Protons
42
__ ___
20
Number of
Neutrons
Number of
Electrons
Atomic
Number
42
9
__
19 ___
19
Mass
Number
18
19
+2
24
12 Mg
6. Two unidentified atoms, “Atom A” and “Atom B,” both have a
mass number of 65. From this information, can you tell if they
are atoms of the same element? Explain why or why not.
Explain
7. Two unidentified atoms, “Atom A” and Atom B,” have
different atomic masses. From this information, can you tell if
these atoms are different elements? Explain why or why not.
©2009 Carolina Biological Supply Company