Periodic Properties and the Elements

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Periodic Properties and the Elements

• Sections 7.1-7.3

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Objectives

• Examine the history of the periodic table
• Identify atomic properties that depend on the
  attraction between electrons and nuclei
• Examine periodic trends

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Key Terms

• Valence orbitals
• Effective nuclear charge

• Bonding atomic radius
• Isoelectronic series

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Development of Periodic Table

• Elements in the same group have similar chemical
  properties
• not identical

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Development of Periodic Table

• Dmitri Mendeleev and Lothar Meyer independently
  came to the same conclusion about how elements
  should be grouped

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Development of Periodic Table

• Ex Mendeleev predicted the discovery of
  germanium (which he called eka-silicon) as an
  element with an atomic weight between that of
  zinc and arsenic, but with chemical properties
  similar to those of silicon

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Periodic Trends

• In this chapter, we will rationalize observed
  trends in
• Sizes of atoms and ions
• Ionization energy
• Electron affinity

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Effective Nuclear Charge

• Electrons are both attracted to the nucleus and
  repelled by other electrons
• The nuclear charge that an electron experiences
  depends on both factors

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Effective Nuclear Charge

• The effective nuclear charge, Zeff, is found
  this way
• Zeff Z - S
• where Z is the atomic number and S is a
  screening constant, usually close to the number
  of inner electrons

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Sizes of Atoms

• Atomic radius 1/2 of the distance between
  covalently bonded nuclei

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Sizes of Atoms

• Bonding atomic radius tends to
• decrease from left to right across a row
• due to increasing Zeff.
• increase from top to bottom of a column
• due to increasing value of n

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• Periodic Trends Atomic Radius

DECREASES
I N C R E A S E S
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Sizes of Ions

• Ionic size depends upon
• Nuclear charge
• Number of electrons
• Orbitals in which electrons reside

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Sizes of Ions

• Cations are smaller than their parent atoms
• The outermost electron is removed and repulsions
  are reduced

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Sizes of Ions

• Anions are larger than their parent atoms
• Electrons are added and repulsions are increased

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Sizes of Ions

• Ions increase in size as you go down a column
• Due to increasing value of n

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Sizes of Ions

• In an isoelectronic series, ions have the same
  number of electrons.
• Ionic size decreases with an increasing nuclear
  charge.

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Homework

• 7.13 and 7.14 page 292
• 7.23, 7.24, and 7.26 7.29 and 7.30 page 293