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Introductory Chemistry - 1st Canadian Edition: Electronic Structure and the Periodic Table

Introductory Chemistry - 1st Canadian Edition
Electronic Structure and the Periodic Table
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table of contents
  1. Cover
  2. Title Page
  3. Copyright
  4. Table Of Contents
  5. Acknowledgments
  6. Dedication
  7. About BCcampus Open Education
  8. Chapter 1. What is Chemistry
    1. Some Basic Definitions
    2. Chemistry as a Science
  9. Chapter 2. Measurements
    1. Expressing Numbers
    2. Significant Figures
    3. Converting Units
    4. Other Units: Temperature and Density
    5. Expressing Units
    6. End-of-Chapter Material
  10. Chapter 3. Atoms, Molecules, and Ions
    1. Acids
    2. Ions and Ionic Compounds
    3. Masses of Atoms and Molecules
    4. Molecules and Chemical Nomenclature
    5. Atomic Theory
    6. End-of-Chapter Material
  11. Chapter 4. Chemical Reactions and Equations
    1. The Chemical Equation
    2. Types of Chemical Reactions: Single- and Double-Displacement Reactions
    3. Ionic Equations: A Closer Look
    4. Composition, Decomposition, and Combustion Reactions
    5. Oxidation-Reduction Reactions
    6. Neutralization Reactions
    7. End-of-Chapter Material
  12. Chapter 5. Stoichiometry and the Mole
    1. Stoichiometry
    2. The Mole
    3. Mole-Mass and Mass-Mass Calculations
    4. Limiting Reagents
    5. The Mole in Chemical Reactions
    6. Yields
    7. End-of-Chapter Material
  13. Chapter 6. Gases
    1. Pressure
    2. Gas Laws
    3. Other Gas Laws
    4. The Ideal Gas Law and Some Applications
    5. Gas Mixtures
    6. Kinetic Molecular Theory of Gases
    7. Molecular Effusion and Diffusion
    8. Real Gases
    9. End-of-Chapter Material
  14. Chapter 7. Energy and Chemistry
    1. Formation Reactions
    2. Energy
    3. Stoichiometry Calculations Using Enthalpy
    4. Enthalpy and Chemical Reactions
    5. Work and Heat
    6. Hess’s Law
    7. End-of-Chapter Material
  15. Chapter 8. Electronic Structure
    1. Light
    2. Quantum Numbers for Electrons
    3. Organization of Electrons in Atoms
    4. Electronic Structure and the Periodic Table
    5. Periodic Trends
    6. End-of-Chapter Material
  16. Chapter 9. Chemical Bonds
    1. Lewis Electron Dot Diagrams
    2. Electron Transfer: Ionic Bonds
    3. Covalent Bonds
    4. Other Aspects of Covalent Bonds
    5. Violations of the Octet Rule
    6. Molecular Shapes and Polarity
    7. Valence Bond Theory and Hybrid Orbitals
    8. Molecular Orbitals
    9. End-of-Chapter Material
  17. Chapter 10. Solids and Liquids
    1. Properties of Liquids
    2. Solids
    3. Phase Transitions: Melting, Boiling, and Subliming
    4. Intermolecular Forces
    5. End-of-Chapter Material
  18. Chapter 11. Solutions
    1. Colligative Properties of Solutions
    2. Concentrations as Conversion Factors
    3. Quantitative Units of Concentration
    4. Colligative Properties of Ionic Solutes
    5. Some Definitions
    6. Dilutions and Concentrations
    7. End-of-Chapter Material
  19. Chapter 12. Acids and Bases
    1. Acid-Base Titrations
    2. Strong and Weak Acids and Bases and Their Salts
    3. Brønsted-Lowry Acids and Bases
    4. Arrhenius Acids and Bases
    5. Autoionization of Water
    6. Buffers
    7. The pH Scale
    8. End-of-Chapter Material
  20. Chapter 13. Chemical Equilibrium
    1. Chemical Equilibrium
    2. The Equilibrium Constant
    3. Shifting Equilibria: Le Chatelier’s Principle
    4. Calculating Equilibrium Constant Values
    5. Some Special Types of Equilibria
    6. End-of-Chapter Material
  21. Chapter 14. Oxidation and Reduction
    1. Oxidation-Reduction Reactions
    2. Balancing Redox Reactions
    3. Applications of Redox Reactions: Voltaic Cells
    4. Electrolysis
    5. End-of-Chapter Material
  22. Chapter 15. Nuclear Chemistry
    1. Units of Radioactivity
    2. Uses of Radioactive Isotopes
    3. Half-Life
    4. Radioactivity
    5. Nuclear Energy
    6. End-of-Chapter Material
  23. Chapter 16. Organic Chemistry
    1. Hydrocarbons
    2. Branched Hydrocarbons
    3. Alkyl Halides and Alcohols
    4. Other Oxygen-Containing Functional Groups
    5. Other Functional Groups
    6. Polymers
    7. End-of-Chapter Material
  24. Chapter 17. Kinetics
    1. Factors that Affect the Rate of Reactions
    2. Reaction Rates
    3. Rate Laws
    4. Concentration–Time Relationships: Integrated Rate Laws
    5. Activation Energy and the Arrhenius Equation
    6. Reaction Mechanisms
    7. Catalysis
    8. End-of-Chapter Material
  25. Chapter 18. Chemical Thermodynamics
    1. Spontaneous Change
    2. Entropy and the Second Law of Thermodynamics
    3. Measuring Entropy and Entropy Changes
    4. Gibbs Free Energy
    5. Spontaneity: Free Energy and Temperature
    6. Free Energy under Nonstandard Conditions
    7. End-of-Chapter Material
  26. Appendix A: Periodic Table of the Elements
  27. Appendix B: Selected Acid Dissociation Constants at 25°C
  28. Appendix C: Solubility Constants for Compounds at 25°C
  29. Appendix D: Standard Thermodynamic Quantities for Chemical Substances at 25°C
  30. Appendix E: Standard Reduction Potentials by Value
  31. Glossary
  32. About the Authors
  33. Versioning History

Electronic Structure and the Periodic Table

Learning Objectives

  1. Relate the electron configurations of the elements to the shape of the periodic table.
  2. Determine the expected electron configuration of an element by its place on the periodic table.

In Chapter 3 “Atoms, Molecules, and Ions”, we introduced the periodic table as a tool for organizing the known chemical elements. A periodic table is shown in Figure 8.12 “The Periodic Table.” The elements are listed by atomic number (the number of protons in the nucleus), and elements with similar chemical properties are grouped together in columns.

The periodic table.
Figure 8.12 “The Periodic Table.” View an accessible periodic table online.

Why does the periodic table have the structure it does? The answer is rather simple, if you understand electron configurations: the shape of the periodic table mimics the filling of the subshells with electrons.

Let us start with H and He. Their electron configurations are 1s1 and 1s2, respectively; with He, the n = 1 shell is filled. These two elements make up the first row of the periodic table (see Figure 8.13 “The 1s Subshell”).

The first row of the periodic table (H and He).
Figure 8.13 “The 1s Subshell.” H and He represent the filling of the 1s subshell.

The next two electrons, for Li and Be, would go into the 2s subshell. Figure 8.14 “The 2s Subshell” shows that these two elements are adjacent on the periodic table.

The left-hand side of the periodic table's second row.
Figure 8.14 “The 2s Subshell.” In Li and Be, the 2s subshell is being filled.

For the next six elements, the 2p subshell is being occupied with electrons. On the right side of the periodic table, these six elements (B through Ne) are grouped together (Figure 8.15 “The 2p Subshell”).

The right-hand side of the periodic table's second row.
Figure 8.15 “The 2p Subshell.” For B through Ne, the 2p subshell is being occupied.

The next subshell to be filled is the 3s subshell. The elements when this subshell is being filled, Na and Mg, are back on the left side of the periodic table (Figure 8.16 “The 3s Subshell”).

The left-hand side of the periodic table's third row.
Figure 8.16 “The 3s Subshell.” Now the 3s subshell is being occupied.

Next, the 3p subshell is filled with the next six elements (Figure 8.17 “The 3p Subshell”).

The right-hand side of the periodic table's third row.
Figure 8.17 “The 3p Subshell.” Next, the 3p subshell is filled with electrons.

Instead of filling the 3d subshell next, electrons go into the 4s subshell, which consists of K and Ca (Figure 8.18 “The 4s Subshell”).

The first two elements of the periodic table's fourth row.
Figure 8.18 “The 4s Subshell.” The 4s subshell is filled before the 3d subshell. This is reflected in the structure of the periodic table.

After the 4s subshell is filled, the 3d subshell is filled with up to 10 electrons. This explains the section of 10 elements in the middle of the periodic table, which consists of Sc to Zn (Figure 8.19 “The 3d Subshell”).

The middle 10 elements of the periodic table's fourth row, from Sc to Zn.
Figure 8.19 “The 3d Subshell.” The 3d subshell is filled in the middle section of the periodic table.

And so forth. As we go across the rows of the periodic table, the overall shape of the table outlines how the electrons are occupying the shells and subshells.

The first two columns on the left side of the periodic table are where the s subshells are being occupied. Because of this, the first two columns of the periodic table are labelled the s block. Similarly, the p block are the right-most six columns of the periodic table, the d block is the middle 10 columns of the periodic table, while the f block is the 14-column section that is normally depicted as detached from the main body of the periodic table. It could be part of the main body, but then the periodic table would be rather long and cumbersome. Figure 8.20 “Blocks on the Periodic Table” shows the blocks of the periodic table.

The s, p, d, and f blocks of the periodic table.
Figure 8.20 “Blocks on the Periodic Table.” The periodic table is separated into blocks depending on which subshell is being filled for the atoms that belong in that section.

The electrons in the highest-numbered shell, plus any electrons in the last unfilled subshell, are called valence electrons; the highest-numbered shell is called the valence shell. (The inner electrons are called core electrons.) The valence electrons largely control the chemistry of an atom. If we look at just the valence shell’s electron configuration, we find that in each column, the valence shell’s electron configuration is the same. For example, take the elements in the first column of the periodic table: H, Li, Na, K, Rb, and Cs. Their electron configurations (abbreviated for the larger atoms) are as follows, with the valence shell electron configuration highlighted:

Table 8.4 Electron Configurations of Elements in the First Column of the Periodic Table
ElementElectron Configuration
H1s1
Li1s22s1
Na[Ne]3s1
K[Ar]4s1
Rb[Kr]5s1
Cs[Xe]6s1

They all have a similar electron configuration in their valence shells: a single s electron. Because much of the chemistry of an element is influenced by valence electrons, we would expect that these elements would have similar chemistry — and they do. The organization of electrons in atoms explains not only the shape of the periodic table but also the fact that elements in the same column of the periodic table have similar chemistry.

The same concept applies to the other columns of the periodic table. Elements in each column have the same valence shell electron configurations, and the elements have some similar chemical properties. This is strictly true for all elements in the s and p blocks. In the d and f blocks, because there are exceptions to the order of filling of subshells with electrons, similar valence shells are not absolute in these blocks. However, many similarities do exist in these blocks, so a similarity in chemical properties is expected.

Similarity of valence shell electron configuration implies that we can determine the electron configuration of an atom solely by its position on the periodic table. Consider Se, as shown in Figure 8.21 “Selenium on the Periodic Table.” It is in the fourth column of the p block. This means that its electron configuration should end in a p4 electron configuration. Indeed, the electron configuration of Se is [Ar]4s23d104p4, as expected.

Selenium is found in the fourth column of the p block and the fourth row of the periodic table.
Figure 8.21 “Selenium on the Periodic Table.”

Example 8.5

Problem

From the element’s position on the periodic table, predict the valence shell electron configuration for each atom. See Figure 8.22 “Various Elements on the Periodic Table.”

  1. Ca
  2. Sn

Solution

  1. Ca is located in the second column of the s block. We would expect that its electron configuration should end with s2. Calcium’s electron configuration is [Ar]4s2.
  2. Sn is located in the second column of the p block, so we expect that its electron configuration would end in p2. Tin’s electron configuration is [Kr]5s24d105p2.

Test Yourself

From the element’s position on the periodic table, predict the valence shell electron configuration for each atom. See Figure 8.22.

  1. Ti
  2. Cl

Answer

  1. [Ar]4s23d2
  2. [Ne]3s23p5
Varius elements on the periodic table. Long description available.
Figure 8.22 “Various Elements on the Periodic Table.” [Long Description]

Food and Drink App: Artificial Colours

The colour of objects comes from a different mechanism than the colours of neon and other discharge lights. Although coloured lights produce their colours, objects are coloured because they preferentially reflect a certain colour from the white light that shines on them. A red tomato, for example, is bright red because it reflects red light while absorbing all the other colours of the rainbow.

Many foods, such as tomatoes, are highly coloured; in fact, the common statement “you eat with your eyes first” is an implicit recognition that the visual appeal of food is just as important as its taste. But what about processed foods?

Many processed foods have food colourings added to them. There are two types of food colourings: natural and artificial. Natural food colourings include caramelized sugar for brown; annatto, turmeric, and saffron for various shades of orange or yellow; betanin from beets for purple; and even carmine, a deep red dye that is extracted from the cochineal, a small insect that is a parasite on cacti in Central and South America. (That’s right: you may be eating bug juice!)

Some colourings are artificial. In the United States, the Food and Drug Administration currently approves only seven compounds as artificial colourings in food, beverages, and cosmetics:

  1. FD&C Blue #1: Brilliant Blue FCF
  2. FD&C Blue #2: Indigotine
  3. FD&C Green #3: Fast Green FCF
  4. RD&C Red #3: Erythrosine
  5. FD&C Red #40: Allura Red AC
  6. FD&C Yellow #5: Tartrazine
  7. FD&C Yellow #6: Sunset Yellow FCF

Lower-numbered colours are no longer on the market or have been removed for various reasons. Typically, these artificial colourings are large molecules that absorb certain colours of light very strongly, making them useful even at very low concentrations in foods and cosmetics. Even at such low amounts, some critics claim that a small portion of the population (especially children) is sensitive to artificial colourings and urge that their use be curtailed or halted. However, formal studies of artificial colourings and their effects on behaviour have been inconclusive or contradictory. Despite this, most people continue to enjoy processed foods with artificial colouring (like those shown in the accompanying figure).

Bottles of green, red, blue, and yellow food colouring.
Figure 8.22a “Food Colouring.” Artificial food colourings are found in a variety of food products, such as processed foods, candies, and egg dyes. Even pet foods have artificial food colouring in them, although it’s likely that the animal doesn’t care!

Key Takeaways

  • The arrangement of electrons in atoms is responsible for the shape of the periodic table.
  • Electron configurations can be predicted by the position of an atom on the periodic table.

Exercises

Questions

  1. Where on the periodic table are s subshells being occupied by electrons?
  2. Where on the periodic table are d subshells being occupied by electrons?
  3. In what block is Ra found?
  4. In what block is Br found?
  5. What are the valence shell electron configurations of the elements in the second column of the periodic table?
  6. What are the valence shell electron configurations of the elements in the next-to-last column of the periodic table?
  7. What are the valence shell electron configurations of the elements in the first column of the p block?
  8. What are the valence shell electron configurations of the elements in the last column of the p block?
  9. From the element’s position on the periodic table, predict the electron configuration of each of the following atoms:
    1. Sr
    2. S
  10. From the element’s position on the periodic table, predict the electron configuration of each of the following atoms:
    1. Fe
    2. Ba
  11. From the element’s position on the periodic table, predict the electron configuration of each of the following atoms:
    1. V
    2. Ar
  12. From the element’s position on the periodic table, predict the electron configuration of each of the following atoms:
    1. Cl
    2. K
  13. From the element’s position on the periodic table, predict the electron configuration of each of the following atoms:
    1. Ge
    2. C
  14. From the element’s position on the periodic table, predict the electron configuration of each of the following atoms:
    1. Mg
    2. I

Answers

  1. the first two columns
  1. the s block
  1. ns2
  1. ns2np1
    1. 1s22s22p63s23p64s23d104p65s2
    2. 1s22s22p63s23p4
    1. 1s22s22p63s23p64s23d3
    2. 1s22s22p63s23p6
    1. 1s22s22p63s23p64s23d104p2
    2. 1s22s22p2

Long Descriptions

Figure 8.22 description: Various elements on the periodic table.

Ca (calcium) is in the second column from the left and the fourth row.

Ti (titanium) is in the fourth column from the left and the fourth row.

Cl (chlorine) is in the second column from the right and the second row.

Sn (tin) is in the fifth column from the right and the fifth row.

[Return to Figure 8.22]

Media Attributions

  • “The Periodic Table” by David W. Ball © CC BY-NC-SA (Attribution NonCommercial ShareAlike)
  • “The 1s Subshell” by David W. Ball © CC BY-NC-SA (Attribution NonCommercial ShareAlike)
  • “The 2s Subshell” by David W. Ball © CC BY-NC-SA (Attribution NonCommercial ShareAlike)
  • “The 2p Subshell” by David W. Ball © CC BY-NC-SA (Attribution NonCommercial ShareAlike)
  • “The 3s Subshell” by David W. Ball © CC BY-NC-SA (Attribution NonCommercial ShareAlike)
  • “The 3p Subshell” by David W. Ball © CC BY-NC-SA (Attribution NonCommercial ShareAlike)
  • “The 4s Subshell” by David W. Ball © CC BY-NC-SA (Attribution NonCommercial ShareAlike)
  • “The 3d Subshell” by David W. Ball © CC BY-NC-SA (Attribution NonCommercial ShareAlike)
  • “Blocks on the Periodic Table” by David W. Ball © CC BY-NC-SA (Attribution NonCommercial ShareAlike)
  • “Selenium on the Periodic Table” by David W. Ball © CC BY-NC-SA (Attribution NonCommercial ShareAlike)
  • “Various Elements on the Periodic Table” by David W. Ball © CC BY-NC-SA (Attribution NonCommercial ShareAlike)
  • “Food Colouring” by Matthew Bland © CC BY (Attribution)

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Copyright © 2014

                                by Jessie A. Key

            Introductory Chemistry - 1st Canadian Edition by Jessie A. Key is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.
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