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Chapter 7. Periodic Properties of the Elements
Media Resources
Figures and Tables in Transparency Pack: Section:
Figure 7.2 Effective Nuclear Charge 7.2 Effective Nuclear Charge
Figure 7.3 2s and 2p Radial Probability Functions 7.2 Effective Nuclear Charge
Figure 7.4 Variations in Effective Nuclear Charge 7.2 Effective Nuclear Charge
for Period 2 and Period 3 Elements
Figure 7.6 Trends in Bonding Atomic Radii for 7.3 Sizes of Atoms and Ions
Periods 1 through 5
Figure 7.7 Cation and Anion Size 7.3 Sizes of Atoms and Ions
Activities: Section:
Periodic Table 7.1 Development of the Periodic Table
Ionization Energies 7.4 Ionization Energy
Animations: Section:
Periodic Properties 7.1 Development of the Periodic Table
Effective Nuclear Charge 7.2 Effective Nuclear Charge
Periodic Trends: Atomic Radii 7.3 Sizes of Atoms and Ions
Movies: Section:
Sodium and Potassium in Water 7.7 Trends for Group 1A and 2A Metals
Chapter 7
88
Reactions with Oxygen 7.8 Trends for Selected Nonmetals
3-D Models: Section:
Methanethiol (methyl mercaptan) 7.3 Sizes of Atoms and Ions
Water 7.6 Metals, Nonmetals, and Metalloids
Other Resources
Further Readings: Section:
Chemical and Engineering News, September 8, 7.1 Development of the Periodic Table
2003
Using the Learning Cycle to Introduce Periodicity 7.1 Development of the Periodic Table
The Nuts and Bolts of Chemistry 7.1 Development of the Periodic Table
Mendeleev and Moseley: The Principal 7.1 Development of the Periodic Table
Discoverers of the Periodic Law
Using Balls from Different Sports to Model the 7.3. Sizes of Atoms and Ions
Variation of Atomic Sizes
Periodic Contractions Among the Elements; Or, 7.3 Sizes of Atoms and Ions
On Being the Right Size
Ionization Energies of Atoms and Atomic Ions 7.4 Ionization Energy
Trends in Ionization Energy of Transition-Metal 7.4 Ionization Energy
Elements
Periodic Properties of the Elements
89
Life, Death, and Calcium 7.7 Trends for Group 1A and 2A Metals
A Second Note on the Term ‘Chalcogen’ 7.8 Trends for Selected Nonmetals
Allotropes and Polymorphs 7.8 Trends for Selected Nonmetals
The Chemistry of Swimming Pool Maintenance 7.8 Trends for Selected Nonmetals
Live Demonstrations: Section:
Halogens Compete for Electrons 7.5 Electron Affinities
Acidic and Basic Properties of Oxides 7.6 Metals, Nonmetals, and Metalloids
Chapter 7
90
Chapter 7. Periodic Properties of the Elements
Common Student Misconceptions
• Students have difficulty with the concepts of shielding and effective nuclear charge. As you move to
the right in a period, shielding does not increase appreciably but the nuclear charge does. Therefore,
effective nuclear charge increases steadily as you move to the right along the period.
Teaching Tips
• Students need to be shown how position on the periodic table and electron configurations can be used
to highlight periodic properties.
Lecture Outline
7.1 Development of the Periodic Table
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• The periodic table is the most significant tool that chemists use for organizing and recalling chemical
facts.
• Elements in the same column contain the same number of outer-shell electrons or valence electrons.
• How do we organize the different elements in a meaningful way that will allow us to make
predictions about undiscovered elements?
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“Periodic Properties” Animation from Instructor’s Resource CD/DVD
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“Periodic Table” Activity from Instructor’s Resource CD/DVD
Periodic Properties of the Elements
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• Arrange elements to reflect the trends in chemical and physical properties.
• The periodic table arises from the periodic patterns in the electronic configurations of the elements.
• Elements in the same column contain the same number of valence electrons.
FORWARD REFERENCES
• Periodic trends and chemical properties of nonmetals will be further discussed in Chapter 22
(section 22.1).
7.2 Effective Nuclear Charge
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• Effective nuclear charge (Zeff) is the charge experienced by an electron on a many-electron atom.
• The effective nuclear charge is not the same as the charge on the nucleus because of the effect of the
inner electrons.
• The electron is attracted to the nucleus, but repelled by electrons that shield or screen it from the full
nuclear charge.
7.3 Sizes of Atoms and Ions
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• Consider a collection of argon atoms in the gas phase.
• When they undergo collisions, they ricochet apart because electron clouds cannot penetrate each
other to a significant extent.
• The apparent radius is determined by the closest distances separating the nuclei during such
collisions.
Chapter 7
92
covalent radius of the atom.
Periodic Trends in Atomic Radii
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• Atomic size varies consistently through the periodic table.
• As we move down a group, the atoms become larger.
• As we move across a period, atoms become smaller.
Periodic Trends in Ionic Radii
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• Ionic size is important:
• in predicting lattice energy and
• in determining the way in which ions pack in a solid.
• Just as atomic size is periodic, ionic size is also periodic.
• In general:
• Cations are smaller than their parent atoms.
• Electrons have been removed from the most spatially extended orbital.
FORWARD REFERENCES
• Sizes and charges of ions will be instrumental in determining lattice energies (Chapter 8).
• Structures of ionic solids in Chapter 12 (section 12.2).
• Atomic radii will affect relative strengths of binary acids of nonmetals from a given group, as
discussed in Chapter 16 (section 16.10).
• Periodic properties of nonmetals in groups 4A-8A are tabulated throughout Chapter 22.
• Periodic properties for the first transition-series elements are shown in Chapter 23 (section
23.1).
Periodic Properties of the Elements
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7.4 Ionization Energy
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• The ionization energy of an atom or ion is the minimum energy required to remove an electron from
the ground state of the isolated gaseous atom or ion.
Variations in Successive Ionization Energies
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• Ionization energies for an element increase in magnitude as successive electrons are removed.
• As each successive electron is removed, more energy is required to pull an electron away from an
increasingly more positive ion.
• A sharp increase in ionization energy occurs when an inner-shell electron is removed.
Periodic Trends in First Ionization Energies
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• Ionization energy generally increases across a period.
• As we move across a period, Zeff increases, making it more difficult to remove an electron.
• Two exceptions are removing the first p electron and removing the fourth p electron.
Electron Configurations of Ions
• These are derived from the electron configurations of elements with the required number of electrons
added or removed from the most accessible orbital.
• Li: [He]2s1 becomes Li+: [He]
• F: [He]2s22p5 becomes F-: [He]2s22p6 = [Ar]
Chapter 7
94
when an electron configuration of the parent atom was written.
FORWARD REFERENCES
• Octet rule will be introduced in Chapter 8.
• Discussion of electron configurations of the representative elements and transition metals will
continue in Chapter 8.
• Photoionization processes and ionization energies will be linked together in Chapter 18.
(section 18.1).
7.5 Electron Affinities
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• Electron affinity is the energy change when a gaseous atom gains an electron to form a gaseous ion.
• Electron affinity and ionization energy measure the energy changes of opposite processes.
• Electron affinity: Cl(g) + e– → Cl–(g) ∆E = –349 kJ/mol
7.6 Metals, Nonmetals, and Metalloids
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• Metallic character refers to the extent to which the element exhibits the physical and chemical
properties of metals.
• Metallic character increases down a group.
• Metallic character decreases from left to right across a period.
Metals
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• Metals are shiny and lustrous, malleable and ductile.
• Metals are solids at room temperature (exception: mercury is liquid at room temperature; gallium and
cesium melt just above room temperature) and have very high melting temperatures.
33
“Electron Affinity” Animation from Instructor’s Resource CD/DVD
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“Periodic Trends: Electron Affinity” Animation from Instructor’s Resource CD/DVD
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Figure 7.11 from Transparency Pack
36
“Halogens Compete for Electrons” from Live Demonstrations
Periodic Properties of the Elements
95
• Metals tend to have low ionization energies and tend to form cations easily.
• Metals tend to be oxidized when they react.
Nonmetals
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• Nonmetals are more diverse in their behavior than metals.
• In general, nonmetals are nonlustrous, are poor conductors of heat and electricity, and exhibit lower
melting points than metals.
• Seven nonmetallic elements exist as diatomic molecules under ordinary conditions:
Metalloids
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• Metalloids have properties that are intermediate between those of metals and nonmetals.
• For example, Si has a metallic luster but it is brittle.
• Metalloids have found fame in the semiconductor industry.
FORWARD REFERENCES
• The role of metals and metalloids in semiconductors will be discussed in Chapter 12 (section
7.7 Trends for Group 1A and Group 2A Metals
• The alkali metals (group 1A) and the alkaline earth metals (group 2A) are often called the active
metals.
Chapter 7
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Group 1A: The Alkali Metals
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• The alkali metals are in Group 1A.
• Alkali metals are all soft.
• Their chemistry is dominated by the loss of their single s electron:
M → M+ + e–
• Reactivity increases as we move down the group.
• Alkali metals react with hydrogen to form hydrides.
• In hydrides, the hydrogen is present as H–, called the hydride ion.
2M(s) + H2(g) → 2MH(s)
Group 2A: The Alkaline Earth Metals
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• Alkaline earth metals are harder and more dense than the alkali metals.
• Their chemistry is dominated by the loss of two s electrons:
M → M2+ + 2e–
7.8 Trends for Selected Nonmetals
Hydrogen
• Hydrogen is a unique element.
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Table 7.4 from Transparency Pack
49
“Sodium and Potassium in Water” Movie from Instructor’s Resource CD/DVD
50
“Flame Tests for Metals” Movie from Instructor’s Resource CD/DVD
51
“A Dramatic Flame Test Demonstration” from Live Demonstrations
Periodic Properties of the Elements
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• It most often occurs as a colorless diatomic gas, H2.
• Reactions between hydrogen and nonmetals can be very exothermic:
2H2(g) + 2O2(g) → 2H2O(l) ∆H° = –571.7 kJ
Group 6A: The Oxygen Group
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• As we move down the group, the metallic character increases.
• O2 is a gas, Te is a metalloid, Po is a metal.
• Two of the important forms of oxygen are O2 and ozone, O3.
• O2 and O3 are allotropes.
• Allotropes are different forms of the same element in the same state (in this case, gaseous).
Group 7A: The Halogens
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• Group 7A elements are known as the halogens ("salt formers").
• The chemistry of the halogens is dominated by gaining an electron to form an anion:
X2 + 2e– → 2X–
• Fluorine is one of the most reactive substances known:
2F2(g) + 2H2O(l) → 4HF(aq) + O2(g) ∆H = –758.9 kJ
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Table 7.6 from Transparency Pack
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“A Second Note on the Term Chalcogen” from Further Readings
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“Preparation and Properties of Oxygen” from Live Demonstrations
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“Plastic Sulfur” from Live Demonstrations
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“Allotropes and Polymorphs” from Further Readings
Chapter 7
98
• All halogens consist of diatomic molecules, X2.
• Chlorine is the most industrially useful halogen.
Group 8A: The Noble Gases
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• The group 8A elements are known as the noble gases.
• These are all nonmetals and monoatomic.
• They are notoriously unreactive because they have completely filled s and p subshells.
FORWARD REFERENCES
• Electron configurations of noble gases and the octet rule will be introduced in Chapter 8
(section 8.1).
• The role of the expanded octet in the formation of compounds involving heavier noble gas
atoms will be discussed in Chapter 8 (section 8.7).
Periodic Properties of the Elements
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Further Readings:
1. The September 8, 2003 issue of Chemical and Engineering News is a special issue celebrating the
periodic table of the elements on C&EN’s 80th anniversary. Approximately 90 short articles, each
featuring a different element, are found in this issue.
5. Eric R. Scerri, “The Evolution of the Periodic System,” Scientific American, September 1998, 78–83.
6. Harold Goldwhite, “Mendeleev’s Other Prediction,” J. Chem. Educ., Vol. 56, 1979, 35–36.
7. Jan W. van Spronsen, “Atomic Number before Moseley,” J. Chem. Educ., Vol. 56, 1979, 106.
11. Kimberley A. Waldron, Eric M. Fehringer, Amy E. Streeb, Jennifer E. Trosky, and Joshua J. Pearson,
“Screen Percentages Based on Slater Effective Nuclear Charge as a Versatile Tool for Teaching Periodic
Trends,” J. Chem. Educ., Vol. 78, 2001, 635–639.
12. John J. Fortman, “Pictorial Analogies VI: Radial and Angular Wave Function Plots,” J. Chem. Educ.,
Vol. 70, 1993, 549–550. Analogies for explaining probability distributions are presented.
13. Gabriel Pinto, “Using Balls from Different Sports to Model the Variation of Atomic Sizes,” J. Chem.
Educ., Vol. 75, 1998, 725–726. This reference involves analogies to investigate atomic and ionic radii.
Chapter 7
100
17. Ronald L. Rich, “Periodicity in the Acid-Base Behavior of Oxides and Hydroxides,” J. Chem. Educ.,
Vol. 62, 1985, 44. This article provides further information on the solubility of various oxides and
hydroxides.
21. Joseph D. Ciparick and Richard F. Jones, “A Variation on the Demonstration of the Properties of the
Alkali Metals,” J. Chem. Educ., Vol. 66, 1988, 438.
22. G. Marino, “Update on Intake: Calcium Consumption Low,” Science News, June 18, 1994, p. 390.
23. Malcolm East, “Life, Death and Calcium,” Chemistry in Britain, March 2002, 42–44.
24. Werner Fischer, “A Second Note on the Term ‘Chalcogen’,” J. Chem. Educ., Vol. 78, 2001, 1333.
Live Demonstrations:
1. Lee R. Summerlin, Christie L. Borgford, and Julie B. Ealy, “Halogens Compete for Electrons,”
Chemical Demonstrations, A Sourcebook for Teachers, Volume 2 (Washington: American Chemical
Society, 1988), pp. 60–61. The relative tendency of halogens to gain (or lose) electrons is explored
through the observation of color changes.
2. Bassam Z. Shakhashiri, “Preparation and Properties of Oxygen,” Chemical Demonstrations: A
Handbook for Teachers of Chemistry, Volume 2 (Madison : The University of Wisconsin Press, 1985),
pp. 137–141. Oxygen gas, prepared from H2O2, is used to support combustion reactions.
Periodic Properties of the Elements
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5. Kristin A. Johnson, Rodney Schreiner, and Jon Loring, “A Dramatic Flame Test Demonstration,” J.
Chem. Educ., Vol. 78, 2001, 640–641.
6. Lee. R. Summerlin, Christie L. Borgford, and Julie B. Ealy, “Producing Hydrogen Gas from Calcium
Metal,” Chemical Demonstrations, A Sourcebook for Teachers, Volume 2 (Washington: American
Chemical Society, 1988), pp. 51–52.
