Ionic%20Bonding%20(6.1)

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Ionic Bonding(6.1)
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Review

• Valence Electron - an electron that is in the
  highest occupied energy level of an atom
• Key role in chemical reactions
• The number of the group matches the number of
  valence electrons
• Elements in a group have similar properties
  because they have the same number of valence
  electrons

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Stable Electron Configurations

• When the highest occupied energy level of an atom
  is filled with electrons, the atom is stable and
  not likely to react
• Nobel gases have stable electron configurations
  with eight valence electrons (helium only has
  two)
• The chemical properties of an element depend on
  the number of valence electrons

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• Electron Dot Diagram
• Model of an atom in which each dot represents a
  valence electron
• The symbol at the center represents the nucleus
  and all other electrons in the atom

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Ionic Bonds

• Some elements achieve stable electron
  configurations through the transfer of electrons
  between atoms

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Transfer of Electrons

• Chlorine is one electron short of having 8
  valence electrons
• Sodium has one too many electrons to be stable
• Sodium transfers its extra electron to chlorine
  to make both atoms more stable

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Formation of Ions

• When an atom gains or loses electrons its charge
  is no longer neutral
• Ion - an atom that has a net positive or negative
  electric charge
• Anion - an ion with a negative charge
• Named by using part of the element name plus the
  suffix -ide
• Example Cl- is called a chloride ion
• Cation - an ion with a positive charge
• Named by using the element name
• Example Na is called a sodium ion

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• When an anion and cation are close together the
  form chemical bonds because opposite charges
  attract
• Chemical Bond - the force that holds atoms or
  ions together as a unit
• Ionic Bond -the force that holds cations and
  anions together
• Form when electrons are transferred from one atom
  to another

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Ionization Energy

• Amount of energy used to remove an electron from
  an atom of an element
• The energy allows the electrons to overcome the
  attraction of the protons in the nucleus
• Varies from element to element
• The lower the ionization energy, the easier it is
  to remove an electron from an atom

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Ionic Compounds

• Compounds that contain ionic bonds
• Chemical Formula - a notation that shows what
  elements a compound contains and the ratio of
  atoms or ions of these elements in the compound
• Examples
• Sodium chloride is NaCl
• Magnesium chloride is MgCl2

Subscript is used to show the relative numbers of
atoms of the elements present. If there is only
one atom of an element in the formula no
subscript is used
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Crystal Lattices

• Repeating pattern of ions in fixed positions
• Crystals - solids whose particles are arranged in
  a lattice structure
• Classified into groups based on the shape of
  their crystals
• The arrangement of the ions depends on the ratio
  of ions and their relative sizes

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Properties of Ionic Compounds

• The properties of an ionic compound can be
  explained by the strong attractions among ions
  within a crystal lattice
• Properties
• High melting point because of strong attractions
  between particles more energy needed to
  separate them
• Poor conductor of electricity as solids because
  of the structure but good conductors as liquids
• Crystals shatter when struck because the like
  charged ions repel each other