Coulombic Attraction
What variables will affect the force of attraction
between protons and electrons?
Why?
Coulombic attraction is the attraction between oppositely charged particles. For
example, the protons in the nucleus of an atom have attraction for the electrons
surrounding the nucleus. This is because the pro- tons are positive and the
electrons are negative. The attractive force can be weak or strong. In this
activity, you will explore the strength of attraction between protons and
electrons in various atomic structures.
Summary of Model 1:
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Model 1 – Distance and Attractive Force
A
+
B
+
C
+
0.10 nm
Force of Attraction
(Newtons)
24.0 × 10–9
–
0.20 nm
–
0.30 nm
6.0 × 10–9
2.7 × 10–9
–
1. Which subatomic particles do these symbols represent in Model 1?
2. The subatomic particles in Model 1 should ( attract / ignore / repel ) one
another.
3. Consider the data in Model 1.
a. What are the manipulated and responding variables in the data?
b. Write a complete sentence that describes the observed relationship
between the manipulated and responding variables in Model 1.
4. If the distance between a proton and electron is 0.40 nm, would you expect
the force of attraction to be greater than or less than 2.7 × 10–9 N? Explain
your reasoning?
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5. Which of the values below do you think would best describe the force
between a proton and electron that are 0.60nm apart?
a. 6.90x10-9 N
c. 1.35 x10-9 N
b. 15.0x10-9 N
d. 0.675x10-9 N
Explain your reasoning.
6. As the distance between the proton and electron doubles, the force of
attraction ( twice as strong / half as strong / less than half as strong ).
a. Which forces did you compare?
7. Two protons are 0.10 nm away from one electron as in the diagram below.
Would you expect the force of attraction to be greater than or less than
24.0 × 10–9 N? Explain your reasoning.
0.10 nm
3
Model 2 – Number of Protons and Attractive Force
A
D
E
F
0.10 nm
Force of Attraction
(Newtons)
24.0 × 10–9
0.10 nm
48.0 × 10–9
0.10 nm
72.0 × 10–9
0.10 nm
96.0 × 10–9
8. Consider the data in Model 2.
a. What are the manipulated and responding variables in the data?
b. Write a complete sentence that describes the relationship between the
manipulated and responding variables in Model 2.
9. What would be the attractive force on a single electron if five protons were
in the nucleus of an atom? Show mathematical work to support your
answer.
10. As the number of protons is doubled, the force felt by the electron
( less than doubles / doubles / more than doubles ).
11. What has a greater effect on the force between the proton and electron,
doubling the distance between them or doubling the number of protons?
4
12. Imagine that a second electron were placed to the left of a nucleus
containing two protons (Model 2, set D). Predict the force of attraction on
both the original electron and the second electron. Explain your prediction
with a complete sentence.
0.10 nm
0.10 nm
Read This!
The attractive and repulsive forces in an atom are rather complex. An electron is
attracted to the protons in the nucleus, but it is also repelled by the other
electrons in the atom. It is important to note however that the attractive force
of the nucleus is NOT divided up among the electrons in the atom. Each
electron feels almost the full attractive force of the nucleus (minus the repulsive
effects of other electrons). Compare the diagram below to set D in Model 2.
Notice the similarity in attractive force.
0.10 nm
0.10 nm
A little less than
48.0 × 10–9 N
A little less than
48.0 × 10–9 N
13. If the force from the nucleus is felt by all electrons equally, why is the force
felt by each of the two electrons a little less than the force felt if there were
only one electron?
14. Label the approximate force on each electron in the diagram below?
0.10 nm
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(Don’t Start Until At Periodic Trends) Model 3 – The Alkali Metals
Sodium
Potassium
Lithium
+3
+11
+19
Stronger Force of Attraction
15. Consider the diagrams in Model 2.
a. What do the arrows represent?
b. How does the length of the arrows relate to the property in part a?
16. Using a periodic table, locate the elements in Model 2. The three elements
above are in the same ( vertical Group / horizontal Period ).
17. When you move down the period table what three key things change about
the atom?
a.
b.
c.
18. Circle the valence electron in each of the diagrams in Model 2.
a. As you move from the smallest atom to the largest atom in Model 2,
does the distance between the valence electrons and the nucleus
increase or decrease? Explain why the distance changes.
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b. As you move from the smallest atom to the largest atom in Model 2,
how does the attractive force between the valence electron and the
nucleus change? How do you know this?
c. Are your answers to parts a and b consistent with the information in
Model 1? Explain your reasoning.
19. As you move from lithium to potassium the number of protons increases
from ______ in Li to ______ in K. The large number of protons in potassium
should result in a ( smaller / larger ) force of attraction, but it doesn’t. Use
what you learned from Model 1 to explain why the valence electrons in
potassium feel a smaller force even though there are more protons pulling
on them.
20. What has a bigger impact on the amount of force that electrons feel, their
distance from the nucleus or the number of protons in the nucleus?
Support your answer with numbers from model 1 and 2.
21. Consider the force of attraction between the valence electrons and the
nucleus in an atom of francium, which has 87 protons in its nucleus and
_____ energy levels in its electron cloud. Explain your reasoning.
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Model 4 – Period 3 Elements
Sodium
Aluminum
Chlorine
+11
+13
+17
22. Using the periodic table, locate the elements in Model 4. These elements
are in the same ( vertical Group / horizontal Period )?
23. As you move from left to right across a period on the periodic table, what
two key things change about the atom?
24. Circle the valence electron(s) in each of the atoms in Model 4.
25. Which of the three atoms in Model 4 has the strongest attraction for its
valence electron(s)? How do you know this?
26. Consider the information in Model 4.
a. As you move across the periodic table, does the distance between the
valence electron(s) and the nucleus change significantly? Explain why.
b. Can the differences in the attractive force shown by the arrows be
explained by a change in the distance between the electron(s) and the
nucleus? Explain your reasoning.
c. Can the differences in attractive forces shown by the arrows in Model 4
be explained by a change in the number of protons in the nucleus? If
yes, explain the relationship in Model 4.
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Read This!
In reality, the atoms in Model 4 get a little smaller as you move across the
periodic. This trend is illustrated in below. This happens because the larger
number of protons in the chlorine nucleus pull the electrons in harder, causing
them to move closer the nucleus.
Sodium
Aluminum
Chlorine
Notice that every energy level in
the chlorine atoms is smaller than
that of an aluminum atom.
+11
+13
+17
27. In your own words, explain why a chlorine atom is smaller than a sodium
atom.
28. For each set of elements below, circle the element whose atoms will have a
stronger attractive force between their valence electron(s) and the nucleus.
a. Ba and Ca
c. Ar and Xe
e. C and O
b. Cr and Cu
d. S and P
f.
Na and P
29. Consider the atom diagrams in Model 3.
a. When comparing elements in the same vertical Group of the periodic
table, which factor—distance to the nucleus or number of protons in the
nucleus—seems to be the dominant factor for determining the trend in
attractive force between the valence electron(s) and the nucleus?
Explain your reasoning.
30. Consider the atom diagrams in Model 4.
a. When comparing elements in the same Period of the periodic table,
which factor—distance to the nucleus or number of protons in the
nucleus—seems to be the dominant factor for determining the trend in
attractive force between the valence electron(s) and the nucleus?
Explain your reasoning.
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