Chapter 4 Homework

1
Chapter 4 Homework

• Due Monday, September 22nd
• P 118 120
• 6, 23, 30, 31, 32, 33, 40, 43, 46, 47

2
ElementsandTheirElectronicConfigurations
3
Shapes of orbitals (electron probability clouds)

• s orbitals are spherical (1).
• p orbitals are dumbbell shaped (3).
• d orbitals have four lobes (5).
• f orbitals are very complex (7).

4
Quantum Numbers and Orbitals

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Atomos, Atomos!
5
Electron Configuration

• The arrangement of electrons in an atom in the
  ground state.
• Need to learn some simple rules or principles.

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Rules are

• Aufbau principle
• Paulis exclusion principle
• Hunds Rule

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Aufbau Principle

• German for building up.
• An electron occupies the lowest-energy orbital
  that can receive it.
• In Hydrogen, the electron goes into the 1s
  orbital because its the lowest energy orbital.

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8

• A general rule -- they arrange themselves to have
  the lowest possible energy.

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Pauli Exclusion Principle

• No two electrons in the same atom can have the
  same set of four quantum numbers.
• Each electron in the same atom has a unique set
  of quantum numbers.

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10
Hunds Rule

• Equivalent orbitals of equal energy are each
  occupied by one electron before any one orbital
  is occupied by a second electron.

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Hunds Rule (cont.)

• All electrons in singly occupied orbitals have
  the same spin.

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Representing Electron Configurations

• Orbital Notation
• Electron-configuration Notation

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Orbital Notation

• An empty or unoccupied orbital is represented by
  a line,

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Orbital Notation

• An orbital containing a single electron is
  represented by

?
15
Orbital Notation

• An orbital containing two electrons is
  represented as

??
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Orbital Notation (cont.)

• An orbital containing three electrons is
  represented as ?

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Writing Electron Configurations
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Orbital Notation (cont.)

• The lines are labeled with the principal quantum
  number and subshell letter.
• Example He
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19
Nitrogen

• How many electrons?
• Orbital Notation?

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Electron-configuration Notation

• No lines, no arrows.
• Number of electrons in a sublevel is shown by
  adding superscripts to the sublevel designation
• Hydrogen would be 1s1

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21
Highest Occupied Energy Level

• The highest occupied energy level is the
  electron-containing level with the highest
  principle quantum number.

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Highest Occupied Energy Level Outer Shell
Electrons

• Important electrons because only they are the
  ones involved in chemical reactions
• Also known as valence electrons

23
Inner Shell (Core) Electrons

• All the other electrons which are not in the
  highest occupied energy level not involved in
  chemical reactions

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Noble Gas Notationa Shortcut!

• Ne 1s22s22p6
• Sodium Ne3s1

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25
Practice Problems

• Write the electron configuration of Sulfur,
  (Z16).
• How many inner-shell electrons does a sulfur atom
  contain?

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Practice

• Ne3s23p1, which element does this represent?
• Write its complete electron configuration.
• How many inner-shell electrons do its atoms
  contain?

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(cont.)

• Write the electron configurations for argon.
  (Z18)
• How many outer-shell electrons do atoms of argon
  contain?

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Elements of the Second Period

• See table 4-3 p. 110
• Li, Be, B, C, N, O, F, Ne
• The second shell is being filled
• Lets move em out and Aufbau em up.

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Elements of the Third Period

• See table 4-4 p. 111
• Na, Mg, Al, Si, P, S, Cl, Ar
• The third shell is being filled
• Lets move em out and Aufbau em up.

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Elements of the Fourth Period

• Potassium thru Krypton
• See Table 4-5 p 112
• Heres where you need to know that the 4s fills
  before the 3d
• The electron configuration of Potassium (Z19) is
  Ar4s1

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(cont.)

• Two elements later (Z21) we get to Scandium
  Ar3d14s2

• Scandium is the first transition metal element

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Exceptions to Aufbau

• Chromium (Z24)
• You would expect Ar3d44s2
• But it is Ar3d54s1

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Why?

• Ar3d54s1
• All six electrons have the same spin.
• The 3d and the 4s are half filled.
• These stability factors decrease the total energy
  of this config.

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Exceptions to Aufbau

• The Aufbau Principal does not work for atoms of
  all elements some elements that deviate are
• Cr, Cu, Ag, Au, Pd, Pt, and Mo.

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Electron Confirguration Notations for Zn through
Kr

• Zn (Z30) Ar3d104s2
• Ga (Z31) Ar3d104s24p1
• Ge (Z32) Ar3d104s24p2
• As (Z33) Ar3d104s24p3

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(cont.)

• Se (Z34) Ar3d104s24p4
• Br (Z35) Ar3d104s24p5
• Kr (Z36) Ar3d104s24p6

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Sample problems p. 114

• Write both the complete and noble-gas electron
  configurations for Fe (Z26).
• 1s22s22p63s23p63d64s2
• Ar3d64s2

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(cont)

• How many electron containing orbitals are there
  in Fe?
• 15
• How many of these orbitals are filled?
• 11

39
(cont.)

• How many unpaired electrons are indicated in the
  electron-configuration notation of an iron atom?
• 4
• Iron is Ferromagnetic!

40
Practice (p. 115)

• Write both the complete electron configuration
  notation and the noble-gas notation for iodine, I
  (Z 53)

• 1s22s22p63s23p63d104s24p64d105s25p5

Kr 4d105s25p5
41
Sixth Period

• The sixth period has 32 elements.
• Z55 to Z86 Cs to Rn
• Uses, beginning with Ce, the 4f orbitals.
• How many f orbitals are there?

42
Seventh Period

• The seventh period is incomplete and consists of
  largely unstable, radioactive elements.
• When we are out to the 6th and 7th periods there
  are many deviations from our simple rules

43
Identify.

• 1s22p22p63s23p3
• P
• Ar4s1
• K

44
Identify.

• Element that contains four electrons in its third
  and outer main energy level.
• Si

45
Identify.

• The third element to contain a d electron.
• V

46

• Write (1)complete, (2)Noble-gas electron
  configurations, (3)orbital
• C (Z6),
• Ne (Z10),
• S (Z16).

47
Electronic Configuration Practice Worksheet (with
Answers)

• Lesson 3-6 Electron Configuration

48
Writing Electron Configurations
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