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NAME_________________________________
PERIODIC TRENDS Summer Assignment 2014
You will need internet access to complete this assignment. You can use other resources as needed.
I. Introduction – read carefully!
In the late 1800’s, Dmitrii Mendeleev first proposed a table in which the elements are arranged according
to physical and chemical properties. This table has been modified since that time, but physical and chemical
properties can still be predicted using the periodic table. Trends in various properties can be observed both across
periods and down groups. However, deviations from the trends may occur in a variety of properties. These
variations can usually be explained by electron-electron repulsion, nucleus-electron attraction, or shielding.
Electron configuration and orbital diagrams are helpful tools to help determine the primary effects involved in the
trends as well as deviations from the trend.
In this activity, you will use computer program, the internet and your test to explore the periodic trends of
the following properties: Atomic size, ionic radii, ionization energy, electron affinity, electronegativity and
oxidation numbers. These trends will be explained in terms of the structure of the atoms. Since structure
determines function, a complete understanding of how the structure of the atom affects the function of the atom
will complete our study of atomic structure.
Exact values of atomic size are difficult to determine because atomic wave functions describe probability
distributions and do not have sharp boundaries. Atomic radii can be estimated from data on bond lengths me
measuring the interatomic distance and dividing by two. Even though data from various methods of measurement
can vary, the trends can be studied as long as the atomic radii were all determined by the same method. These
values are usually reported in pm, which is equal to 10-12 m.
The ionization energy is the energy that is required to remove an electron from an atom in the gaseous
phase. You will study sequential ionization energy processes. During the analysis, be cognizant of from which
sublevel and orbital an electron is being removed and whether or not the sublevel is full or half-full. It is not
sufficient to explain a trend by stating the sublevel is “full” or “half-full”. Use forces of attraction and repulsion
along with shielding and a simplified view of effective nuclear charge (Zeff).
The electron affinity is a measure of the energy involved in the process of adding an electron to an atom
in the gaseous phase. The electron affinity is strongly affected by the effective nuclear charge. Be careful
interpreting electron affinity! A high electron affinity in the vocabulary sense indicates the addition is exothermic
and thus has a negative value. A low electron affinity
in the vocabulary sense has a positive value.
II. Models
You will be asked to use a variety of models to help
formulate your answers. The energy level diagram to
the right is also a great reference. Notice how close the
energies of n = 3, 4, 5 are to each other in comparison to
n = 1 & 2.
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III. Introductory Terms & Concepts
1. Define the Universal force: Oppositely charged particles _______________ (fill in the blank & finish the
statement)…
2. Describe how these two types of forces are balanced in the ground state arrangement of electrons around
the nucleus
3. Use arrows to diagram these inter-particle forces for the Lithium atom. The helium atom shown on the
left provides a model for you. (What do you think Z stands for?)
4. Define the following terms
a. “SHIELDING” ( see figure for
hints and
http://facultyfp.salisbury.edu/dfrieck/htdocs/212/rev/zeff/shielding.htm )
b. Effective nuclear charge (Wikipedia.org)
Z:
+ 2
─
─
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c. Valence electrons
d. Core electrons
5. Write the electron configuration for tin. Underline the core electrons and circle the valence electrons.
6. Calculate the effective nuclear charge for tin.
7. Would shielding have a greater effect across a period or down a group? Explain.
8. Define and write a generalized equation for the following:
a. Ionization energy
b. Electron Affinity
9. Compare and contrast the terms “electron affinity” and “electronegativity”
ELECTRON AFFINITY ELECTRONEGATIVITY
10. As a generalized principle, will an increase in attraction to the nucleus tend to increase or decrease each
of the following? Explain
a. The size of an atom
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b. The ionization energy
c. The electronegativity
11. As a generalized principle, will an increased repulsion between electrons tend to increase or decrease each
of the following? Explain
a. The size of an atom
b. The ionization energy
c. The electronegativity
IV. Procedure
Log on to the internet and go to www.webelements.com . Click on the “Periodicity” tab at the top, and
then choose the property you are observing. If you are asked to make comparisons, do the graphs separately and
note the scale on the y-axis. It is not necessary to print or draw the graphs. You can also view the trend
directly on the periodic table. Explore the programs to see what works best for you.
All trends and deviations from trends should be explained in terms of the electron configuration,
shielding, effective nuclear charge, and the structure of the atom. Sample electron configurations and/or orbital
diagrams should be used to support the answer. You may use the noble gas configuration only when instructed.
(You do not need to print the graphs.)
V. Analysis
A. Atomic Radii
12. How are atomic radii measured?
13. Use the program to observe the graph of Radius-metallic. Focus on the atomic radii for groups 2 and 17
(or 7A). Describe the trend in the values down a group and provide an explanation for the trend based
on atomic structure.
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14. Observe the atomic radii data for period 4. Describe and explain the periodic trend.
15. Explain why the difference in atomic radii between rubidium and potassium is less than the difference
between sodium and lithium. Refer to the energy level diagram on page one for help
B. Ionic Radii: Go back to the list of periodic trends and look at the graph of Ionic Radius (Pauling).
When you put the cursor on the point for specific elements, the data will be displayed.
16. Compare the atomic radii and the ionic radii on the same graph for each of the groups 2 and 17 (or 7A).
ELEMENT ATOMIC RADII IONIC RADII
Potassium
Strontium
Sulfur
Bromine
a) Which is larger for cation formation: atomic radii or ionic radii (circle one) Explain.
b) Which is larger for anion formation: atomic radii or ionic radii (circle one) Explain.
c) Fill out the following chart. Justify your claim in 16a regarding cation size using atomic structure.
Particle Electron configuration Outer electron
config.
Sr
Sr2+
Justification:
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d) Fill out the following chart. Justify your claim in 16b regarding anion size using atomic structure.
Particle Orbital diagram for n=4 electrons
Br [Ar] ____ ____ ____ ____ ____ ____ ____ ____ ____
4s 3d 4p
Br─
[Ar] ____ ____ ____ ____ ____ ____ ____ ____ ____
4s 3d 4p
Justification:
e) Write the complete electron configurations for the following ions. Determine the number of
subatomic particles in each ion. Rank the ions from smallest (1) to largest (5). Justify your
prediction.
ION ELECTRON CONFIGURATION # of
Protons
# of
Electrons
RANK
P3─ 1s22s22p63s23p6
S2─
Cl─
K+
Ca2+
JUSTIFICATION
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C. Ionization Energies
17. Examine the graph of the 1st ionization energy for periods 2 and 3.
a)
Describe and explain the period trend.
b) Fill in the orbital diagrams below for Mg and Al. Note the 1st ionization energies for these two
elements do not follow the trend. Explain this anomaly (a deviation from the common rule or trend)
observed between Mg and Al in period three.
Mg: [Ne] ____
3s
Al: [Ne] ____ ____ ____ ____
3s 3p
c) Fill in the orbital diagrams below for N and O and explain the anomaly observed between N and O
in period two
N: [He] ____ ____ ____ ____
2s 2p
O: [He] ____ ____ ____ ____
2s 2p
18. Examine the 1st ionization energy for all elements below.
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Look
specifically at the
elements in groups 2 and 16. Describe and explain in terms of the universal force the trend down a group. Are
there exceptions?
19. Look up the 2nd ionization energy for the following representative elements in groups 1, 2, and 13. Fill in
the orbital diagrams and circle the electron that would be removed during the second ionization step.
Why is there such a large difference between the first and second ionization energies in group 1 compared
to groups 2 and 13?
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GROUP 1st
ionization
energy
2nd
ionization
energy
ORBITAL diagram for a representative element. Circle the 2nd
e─ that is removed in each
1
Na
____ ____ ____ ____ ____ ____ ____ ____ ____
1s 2s 2p 3s 3p
2
Mg
____ ____ ____ ____ ____ ____ ____ ____ ____
1s 2s 2p 3s 3p
13
Al
____ ____ ____ ____ ____ ____ ____ ____ ____
1s 2s 2p 3s 3p
Explanation of difference:
20. Examine the table of successive ionization energies in the table below.
Determine whether a valence electron is being removed or a core electron. Where does the largest
increase in ionization energy occur? Explain using atomic structural principles.
21. Write reaction equations for the 1st, 2nd, 3rd ionization for arsenic. Based on the trend observed for
aluminum, where would you predict the major increase in ionization energy to occur for arsenic? Why?
IONIZATION IONIZATION REACTION
1ST
As + IE1 As+ + e-
2ND
3RD
QUESTION ANSWER:
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D. Oxidation Numbers
22. Define the term “oxidation number” or “oxidation state”. (These are synonyms so only one term needs to
be defined.)
On the last page is a periodic table with oxidation numbers listed. Use it to answer these questions.
23. Explain the common oxidation numbers listed below using electron configurations. Write the electron
configuration and CIRCLE the electrons that would be removed for cations. For anion formation,
CIRCLE the orbital/sublevel that would change. Write the electron configurations for the ions formed.
Element ION NOBLE GAS ELECTRON
CONFIGURATION FOR ATOM
NOBLE GAS ELECTRON
CONFIGURATION FOR ION
K +1
Mn +2
+3
+7
Element ION NOBLE GAS ELECTRON
CONFIGURATION FOR ATOM
NOBLE GAS ELECTRON
CONFIGURATION FOR ION
As -3
+3
+5
Br -1
+1
+5
E. Electron affinity & Electronegativity
NOTE: Electron affinity is a measure of the actual energy involved in the process. A negative value is
exothermic and a positive value is endothermic. Since exothermic processes are FAVORABLE, as the VALUE
for the electron affinity becomes more NEGATIVE, the element is said to have a HIGHER affinity in the
vocabulary sense. Seems a little flip-flopped! When in doubt – look for fluorine – the element that has a strong
affinity for electrons. Because this can get confusing, we will study the trends in ELECTRONEGATIVITY.
Electronegativity is a central concept in the discussion of bonding.
1. Graph the electronegativity values for period 3. Describe and explain the general trend.
2. Graph the electronegativity values for group 1. Describe and explain the general trend.
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