CHAPTER 7



CHAPTER 8

Electron Configurations and Periodicity

Chapter Terms and Definitions

Numbers in parentheses after definitions give the text sections in which the terms are explained. Starred terms are italicized in the text. Where a term does not fall directly under a text section heading, additional information is given for you to locate it.

periodic table*  arrangement of the elemental symbols in rows and columns (chapter introduction)

electron configuration  particular distribution of electrons among available subshells (8.1)

orbital diagram  diagram showing how the orbitals of a subshell are occupied by electrons; orbital can hold at most two electrons and then only if the electrons have opposite spins (8.1)

Pauli exclusion principle  no two electrons in an atom can have the same four quantum numbers (8.1)

nuclear magnetic resonance (NMR)*  condition wherein an atomic nucleus with a net spin and magnetism aligned with an external magnetic field is caused to change or “flip” to an alignment against the applied field (Instrumental Methods: Nuclear Magnetic Resonance [NMR])

magnetic resonance imaging (MRI)*  medical diagnostic tool based on nuclear magnetic resonance (Instrumental Methods: Nuclear Magnetic Resonance [NMR])

ground state*  quantum-mechanical state in which an atom is at its lowest energy level (8.2)

excited states*  quantum-mechanical states in which an atom is at energy levels other than the lowest (8.2)

building-up (Aufbau) principle  scheme used to reproduce the electron configuration of the ground states of atoms by successively filling subshells with electrons in a specific order (the building-up order) (8.2)

building-up order*  order in which electrons successively fill the subshells: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d (8.2)

noble gases*  Group VIIIA elements (8.2)

alkaline-earth metals*  Group IIA elements (8.2)

noble-gas core  inner-shell electron configuration corresponding to one of the noble gases (8.2)

pseudo-noble-gas core  noble-gas core together with (n ( 1)d10 electrons (8.2)

valence electron  electron in an atom outside the noble-gas or pseudo-noble-gas core (8.2)

valence-shell configurations*  arrangements of electrons in the outer ns and np subshells (8.2)

main-group (representative) elements*  elements in the A columns of the periodic table, in which an outer s or p subshell is filling (8.2)

d-block transition (transition) elements*  ten columns of elements inserted between Groups IIA and IIIA in the periodic table, in which d subshells are filling (8.2)

f-block transition (inner-transition) elements*   two rows of elements, each with 14 columns, at the bottom of the periodic table, in which f subshells are filling; they fit between Groups IIIB and IVB of Periods 6 and 7 of the periodic table (8.2)

x-ray spectroscopy*  analysis of x rays emitted from a target hit by an electron beam (Instrumental Methods: X Rays, Atomic Numbers, and Orbital Structure [Photoelectron Spectroscopy])

x-ray photoelectron spectroscopy*  analysis of the kinetic energies of electrons ejected from a target irradiated with x rays (Instrumental Methods: X Rays, Atomic Numbers, and Orbital Structure [Photoelectron Spectroscopy])

photoelectric effect*  ejection of electrons from the surface of a metal when light of the proper frequency shines on it (Instrumental Methods: X Rays, Atomic Numbers, and Orbital Structure [Photoelectron Spectroscopy])

ionization energy*  energy necessary to remove an electron from an atom (Instrumental Methods: X Rays, Atomic Numbers, and Orbital Structure [Photoelectron Spectroscopy])

Hund’s rule  the lowest-energy arrangement of electrons in a subshell is obtained by putting electrons into separate orbitals of the subshell with the same spin before pairing electrons (8.4)

paramagnetic substance  substance that is weakly attracted by a magnetic field; generally due to unpaired electrons (8.4)

diamagnetic substance  substance that is not attracted by a magnetic field or is weakly repelled by such a field; generally means the presence of only paired electrons (8.4)

ferromagnetism*  strong, permanent magnetism of iron objects owing to the cooperative alignment of electron spins in many iron atoms (8.4, marginal note)

eka*  Sanskrit word meaning “first” (8.5)

melting point*  temperature at which a solid substance changes to a liquid (8.5)

boiling point*  temperature at which the vapor pressure of a liquid equals the external pressure (8.5)

periodic law  when the elements are arranged by atomic number, their physical and chemical properties vary periodically (8.6)

covalent radii*  lengths of atomic radii obtained from measurements of distances between the nuclei of atoms in the chemical bonds of molecular substances (8.6)

effective nuclear charge  positive charge that an electron experiences from the nucleus, equal to the nuclear charge but reduced by any shielding or screening from any intervening electron distribution (8.6)

first ionization energy (first ionization potential)  minimum energy needed to remove the highest-energy (the outermost) electron from a neutral atom in the gaseous state (8.6)

alkali metals*  Group IA elements (8.6)

electron affinity  energy change for the process of adding an electron to a neutral atom in the gaseous state to form a negative ion (8.6)

basic oxide  oxide that reacts with acids (8.7)

acidic oxide   oxide that reacts with bases (8.7)

amphoteric oxide  oxide that has both acidic and basic properties (8.7)

alloys*  metallic mixtures (8.7, marginal note)

chalogens*  Group VIA elements (8.7)

halogens*  reactive nonmetals with the general molecular formula X2, where X symbolizes a halogen (8.7)

Chapter Diagnostic Test

1. Which of the following electron configurations is(are) incorrect? Give the correct one(s).

a. Al: [Ne] 3s23p1

b. Co: [Ar] 3d84s1

c. Br: [Ar] 4d105s25p5

d. Cs: [Xe] 6s1

e. S: [Ne] 3s23p4

2. Atoms in the same group of the periodic table have the same _____________________________

______________________________________________________________________________

3. Silicon has the following number of valence electrons:

a. two.

b. five.

c. one.

d. eight.

e. none of the above.

4. Determine whether each of the following statements is true or false. If a statement is false, change it so that it is true.

a. The orbital diagram of the nitrogen atom in the ground state is [He] [pic][pic][pic]. True/False: ________________________________________________________________

__________________________________________________________________________

b. Paramagnetism arises when a species has unpaired electrons and is demonstrated experimentally when a sample of the species is attracted into a magnetic field. True/False:___________________________________________________________________________________________________________________________________________

c. According to Hund’s rule, the lowest energy state of an atom will have the maximum number of parallel spins for a given n and l designation. True/False: ____________________________________________________________________________________________________________________________________________________

d. The correct order in increasing size of atomic radii is Na, S, Cs, Ba. True/False: ____________________________________________________________________________________________________________________________________________________

5. Write electron configurations for the following:

a. Sr ________________________________________________________________________

b. Ni _______________________________________________________________________

c. Cl( _______________________________________________________________________

6. Choose the answer (or answers) that will complete the following phrase. The Pauli exclusion principle

a. states that no two electrons in an atom can have the same four quantum numbers.

b. states that the ground-state electron configuration of an atom will have the maximum number of parallel spins.

c. implies that the energy ordering of orbitals depends on the numerical values of n and l.

d. excludes the possibility of having two electrons with opposed spins.

e. determines the number of electrons in each orbital.

7. Following is a labeled drawing of the periodic table:

[pic]

Which of the following sets correctly identifies the labeled parts?

a. A—main group, B—nonmetal, C—transition, D—lanthanide elements

b. A—transition, B—main group, C—inner transition, D—actinide elements

c. A—inner transition, B—transition, C—main group, D—lanthanide and actinide elements

d. A—main group, B—transition, C—main group, D—inner-transition elements

e. None of the above is correct.

8. Of the five atoms Rb, O, P, Sr, and Se, which should exhibit the lowest first ionization potential?

a. Rb

b. O

c. P

d. Sr

e. Se

Answers to Chapter Diagnostic Test

If you missed an answer, study the text section and problem-solving skill (PS Sk.) given in parentheses after the answer.

1.

a. Should be [Ar] 3d74s2

b. Should be [Ar] 3d104s24p5 (8.3, PS Sk. 2)

2. Number of valence electrons and similar chemical and physical properties (8.5, 8.6, PS Sk. 3)

3. e (8.3, PS Sk. 3)

4.

a. False. [He] [pic] [pic] [pic] [pic] (8.1, 8.4, PS Sk. 1, 4)

2s 2p

b. True. (8.4)

c. True. (8.4)

d. False. The correct order is S, Na, Ba, Cs. (8.6, PS Sk. 5)

5.

a. 1s22s22p63s23p63d104s24p65s2, or [Kr] 5s2

b. 1s22s22p63s23p63d84s2, or [Ar] 3d84s2

c. 1s22s22p63s23p6, or [Ar] (8.3, PS Sk. 2)

6. a and e (8.1)

7. e (8.2)

8. a (8.6)

Summary of Chapter Topics

8.1 Electron Spin and the Pauli Exclusion Principle

Learning Objectives

• Define electron configuration and orbital diagram.

• State the Pauli exclusion principle.

• Apply the Pauli exclusion principle. (Example 8.1)

Problem-Solving Skill

1. Applying the Pauli exclusion principle. Given an orbital diagram or electron configuration, decide whether it is possible or not, according to the Pauli exclusion principle (Example 8.1).

You will need to remember the essence of the Pauli exclusion principle to work problems. In short, it is that no two electrons in an orbital can have the same spin.

Exercise 8.1

Look at the following orbital diagrams and electron configurations. Which are possible and which are not, according to the Pauli exclusion principle? Explain.

a. [pic] [pic] [pic] [pic] [pic]

1s 2s 2p

b. [pic] [pic] [pic] [pic] [pic]

1s 2s 2p

c. [pic] [pic] [pic] [pic] [pic]

1s 2s 2p

d. 1s22s22p4

e. 1s22s42p2

f. 1s22s22p63s23p103d10

Known: Pauli exclusion principle (from text)

Solution:

a. Possible.

b. Possible.

c. Impossible; two electrons in a 2p orbital have the same spin.

d. Possible.

e. Impossible; there are four electrons in the 2s subshell.

f. Impossible; there are ten electrons in the 3p subshell.

8.2 Building-Up Principle and the Periodic Table

Learning Objectives

• Define building-up principle.

• Define noble-gas core, pseudo-noble-gas core, and valence electron.

• Define main-group element and (d-block and f-block) transition element.

• A memory device often called the diagonal rule is shown below. It is a very useful aid for writing the arrangement of electrons in atoms.

The diagonal rule:

To obtain the order in which orbitals are filled, start at the right of the bottom arrow and follow it to its point. Then begin at the top right of the next arrow and follow it to its point, and so forth.

It is a good idea to memorize the following exceptions to the building-up principle and their configurations: Cr and Cu in Period 4 and Ag in Period 5. There are others as well. See Appendix D.

8.3 Writing Electron Configurations Using the Periodic Table

Learning Objectives

• Determine the configuration of an atom using the building-up principle. (Example 8.2)

• Determine the configuration of an atom using the period and group numbers. (Example 8.3)

Problem-Solving Skills

2. Determining the configuration of an atom using the building-up principle. Given the atomic number of an atom, write the complete electron configuration for the ground state, according to the building-up principle (Example 8.2).

3. Determining the configuration of an atom using the period and group numbers. Given the period and group for an element, write the configuration of the outer electrons (Example 8.3).

Mendeleev and Meyer found that when the elements were ordered by atomic weight, properties of the main-group elements recurred every eighth element. (The noble gases were not discovered until around 1900.) They arranged the elements in horizontal rows with like elements under one another. The reason for the recurring similarities, we believe, is the recurrence of a similar electron configuration. In our periodic table, arranged by atomic number, all elements in Group (column) IA have one electron in the s subshell of the highest occupied quantum level, n. All elements in Group IIA have two electrons in the s subshell of the highest occupied quantum level, etc. Thus the Group A number is the number of valence electrons. Moreover, each period of the table corresponds to a major quantum level. In Period 1, for example, quantum level 1 is the quantum level that fills.

Thus it is the electrons with their particular energies that are the stars of the chemical drama. In Groups IA and IIA, the s subshell (and orbitals) are filling. In Groups IIIA to VIIIA, the p subshell (and orbitals) are filling, except for helium, in which the 1s sublevel is filled. In the transition metals, the d subshell (and orbitals) are filling, and in the inner-transition metals, the f subshell (and orbitals) are filling.

Once you are comfortable with this quantum level, subshell, and orbital correlation with periodic table groups and sections, you can read the building-up order directly from the table. Begin at the upper left with hydrogen, and read across to helium: 1s1 and 1s2. Then begin at the left again with lithium, 2s1, and continue across to neon, 2p6. Skipping down to potassium, which begins Period 4, you have 4s1, 4s2, then 3d1, etc. (remember the exceptions, chromium and copper). Practice doing this until you can write the electron configurations of main-group elements and at least the 3d transition elements directly from the table.

If you look into the subject, you will find that there are several forms of the periodic table. The one in your text is called the long form. The short form takes less space but is much more difficult to read.

In some texts you will see the lanthanides called lanthanoids and the actinides called actinoids. According to the currently accepted rules in naming compounds, an ionic compound of two elements is a salt and ends in -ide. Recall that NaCl is sodium chloride. Some authors feel that the group names should reflect these rules accurately, and since these substances are elements, they should not be named as salts. Other authors, including your textbook authors, believe that history should be preserved and call them by their original names.

Exercise 8.2

Use the building-up principle to obtain the electron configuration for the ground state of the manganese atom (Z = 25).

Known: The diagonal rule memory aid; Z, the atomic number = number of protons; number of electrons in the neutral atom equals the number of protons = 25; 2(electrons fill an s subshell, 6 fill a p subshell, and 10 fill a d subshell.

Solution: 1s22s22p63s23p64s23d5. To be consistent with the text, we order the shells with 3d before 4s: 1s22s22p63s23p63d54s2, which also could be written [Ar](3d54s2.

Exercise 8.3

Using the periodic table on the inside front cover of the text, write the valence-shell configuration of arsenic (As).

Known: Definition of valence-shell configuration; the period gives the number of the highest occupied quantum level; the Group A number gives the number of valence electrons.

Solution: Arsenic is in Period 4 and Group VA. Its valence-shell configuration is 4s24p3.

Exercise 8.4

The lead atom has the ground-state configuration [Xe] 4f145d106s26p2. Find the period and group for this element. From its position in the periodic table, would you classify lead as a main-group, a transition, or an inner-transition element?

Known: Valence electrons are in the highest occupied quantum level (shell); the quantum number of this level is the period number; the number of valence electrons gives the column (Group) A number.

Solution: The highest occupied quantum level is 6, so lead is in Period 6. There are 4 valence electrons, 2 in the 6s subshell and 2 in the 6p subshell, indicating Group(IVA. In this position, lead is a main-group element.

8.4 Orbital Diagrams of Atoms; Hund’s Rule

Learning Objectives

• State Hund’s rule.

• Apply Hund’s rule. (Example 8.4)

• Define paramagnetic substance and diamagnetic substance.

Problem-Solving Skill

4. Applying Hund’s rule. Given the electron configuration for the ground state of an atom, write the orbital diagram (Example 8.4).

You will need to remember the essence of Hund’s rule to work problems: One electron goes into each orbital of a subshell before two electrons occupy any of them, and all electrons in the singly occupied orbitals have the same spin.

Exercise 8.5

Write an orbital diagram for the ground state of the phosphorus atom (Z = 15). Write all orbitals.

Known: There are 15 electrons to place in the filling order; Hund’s rule; Pauli exclusion principle (no more than 2 electrons per orbital; spins must be opposite).

Solution: First write the electron configuration:

1s22s22p63s23p3

Then write the orbital diagram:

[pic] [pic] [pic][pic][pic] [pic] [pic] [pic] [pic]

1s 2s 2p 3s 3p

8.5 Mendeleev’s Predictions from the Periodic Table

Learning Objective

• Describe how Mendeleev predicted the properties of undiscovered elements.

8.6 Some Periodic Properties

Learning Objectives

• State the periodic law.

• State the general periodic trends in size of atomic radii.

• Define effective nuclear charge.

• Determine relative atomic sizes from periodic trends. (Example 8.5)

• State the general periodic trends in ionization energy.

• Define first ionization energy.

• Determine relative ionization energies from periodic trends. (Example 8.6)

• Define electron affinity.

• State the broad general trend in electron affinity across any period.

Problem-Solving Skill

5. Applying periodic trends. Using the known trends and referring to a periodic table, arrange a series of elements in order by atomic radius (Example 8.5) or ionization energy (Example 8.6).

Exercise 8.6

Using a periodic table, arrange the following in order of increasing atomic radius: Na, Be, Mg.

Known: Size increases down a group (column), decreases across a period; we can get the order from the periodic table.

Solution: Be  Cs

d. Al > Ca > Cs (8.6, PS Sk. 5)

10.

[pic](8.2)

Chapter Post-Test

1. For each of the following pairs, indicate which atom or ion should have the larger radius.

a. Au3+ or Au+

b. Ar or Xe

c. Br or Br(

d. F or I

e. O or B

2. _________________________ electrons are found in the outermost energy level.

3. Which of the following statements about periodic properties of the elements is (are) incorrect?

a. The ionization energies of the elements in a given period generally increase from left to right.

b. The electron affinities of the elements in a given period generally increase from left to right.

c. Chemical properties of the elements are periodic functions of the atomic number.

d. Atomic radii increase across a period and down a group.

e. The ionization energies of the elements generally increase in going down a given group in the periodic table.

4. The element with atomic number 53 has how many electrons in its valence shell?

a. 7

b. 53

c. 8

d. 2

e. 126

5. Write the abbreviated electron configuration for each of the following in the ground state.

a. potassium, Z = 19

b. titanium, Z = 22

c. aluminum, Z = 13

d. Ag, Z = 47

6. The d subshell can accommodate, for any given principal quantum number, the following number of electrons:

a. 6.

b. 14.

c. 2.

d. 10.

e. none of the above.

7. Which of the following orbital diagrams is (are) incorrect for the respective ground-state electron configuration?

|a. 4s23d5 |= |[pic] [pic][pic][pic][pic][pic] |

|b. 4s23d104p4 |= |[pic] [pic][pic][pic][pic][pic] [pic][pic] |

|c. 3s23p3 |= |[pic] [pic][pic][pic] |

|d. 5s1 |= |[pic] |

|e. 4f6 |= |[pic][pic][pic][pic][pic][pic][pic] |

8. Which of the following is (are) diamagnetic?

a. Sn2+

b. F

c. H

d. Si

e. K+

9. Arrange the following sets of atoms in order of increasing first ionization potential.

a. K Cs Rb Li

b. Ga As Br Ca

c. O N Se Te

d. B He Li Ne

10. Given the general trend in electron affinities across any period in the periodic table, explain why the electron affinities of C and N are (122 and 0 kJ/mol, respectively.

11. Explain in simple terms how (or why) the Pauli exclusion principle works.

Answers to Chapter Post-Test

If you missed an answer, study the text section and problem-solving skill (PS Sk.) given in parentheses after the answer.

1.

a. Au+

b. Xe

c. Br(

d. I

e. B (8.6, PS Sk. 5)

2. Valence (8.2)

3. d and e (8.6)

4. a (8.3, PS Sk. 3)

5.

a. [Ar] 4s1

b. [Ar] 3d24s2

c. [Ne] 3s23p1

d. [Kr] 4d105s1 (an exception) (8.3, PS Sk. 2)

6. d (8.1)

7. b (8.1, 8.4, PS Sk. 1, 4)

8. a and e (8.4)

9.

a. Cs  ................
................

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