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Ionic_ Covalent and Metallic Bonding

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					Ionic, Covalent and Metallic
          Bonding
 The type of bond that atoms form
     between them affect the
      substances properties
     Why do atoms form bonds
• Atoms form bonds in order to have a stable
  electron configuration.
• You will recall that Noble Gases are the least
  reactive (most stable) elements. They have 8
  valence electrons making them very stable.
• All atoms try to obtain a stable octet (8
  electrons) in their outer energy level by either
  gaining electrons, losing electrons or sharing
  electrons.
  Bonds can Stretch and Bend
• Because bonds are formed from the attraction
  between the nucleus of an atom and the
  electrons of another atom the bond is not a rigid
  structure but rather a flexible spring-like
  attraction.
• The electrons are in constant motion causing
  the forces of attraction and repulsion to
  constantly change, resulting in the distance
  between two bonded atoms to constantly
  change.
             Ionic Bonds
• Formed between ions of opposite charges.
• The nucleus of one ion attracts the
  electrons of the other ion.
• Ionic bonds are usually formed by the
  transfer of electrons from a metal to a
  nonmetal.
• Cations must free up electrons for the
  anions to accept.
          Ionic Compounds
• Ionic compounds are a network of ions
  and not molecules.
• The simplest ratio of ions that combine to
  form an ionic compound is called a
  formula unit
• The ratio of ions in an ionic compound
  depends on the charges of the ions
Characteristics of Ionic Compounds
• Ionic Compounds:
• are always solids at room temperature
• conduct electricity when dissolved in
  water or in the molten state
• have high melting and boiling points
• are brittle
• are usually white and crystaline
            Metallic Bonds
• Metallic bonds:
• only exist between atoms of two different
  metals or atoms of the same metal
  element.
• Are formed by delocalized valence
  electrons, (electrons that do not belong to
  only one nucleus but are free to move
  from nucleus to nucleus)
        Metallic bonds cont.
• Metals atoms also have an arrangement
  called close packed stacking in which
  atoms stack in layers with the atoms on
  the top layer sitting between atoms on the
  lower layer.
  Characteristics of metallic bonds
• Properties of Metals:
• Malleable ( can be hammered into a thin
  sheet)
• Ductile (can be drawn into a wire)
• Can conduct heat and electricity easily
• Shiny
• All these properties can be attributed to
  the delocalized electrons and the close
  stacking of atoms
          Covalent Bonding
• Covalent Bonds:
• Often form between two nonmetals
• Formed by the sharing of electrons
• Polar covalent bonds are formed when atoms do
  not share electrons equally like in a water
  molecule oxygen attracts the electrons more
  strongly than hydrogen.
• Nonpolar covalent bonds the atoms share the
  electrons equally two identical atoms have
  nonpolar covalent bonds
       Covalent bonds cont.
• Atoms can share more than one pair of
  electrons. These multiple bonds usually
  occur between carbon, oxygen, sulfur, or
  nitrogen atoms.
• The more bonds two atoms share the
  stronger the bond is and the more energy
  that is required to break it.
• Longer bonds are weaker than shorter
  bonds
            Polyatomic ions
• A group of nonmetals that are covalently bonded
  with an overall charge.
• Polyatomic ions are found in ionic compounds
• Most polyatomic ions have a negative charge
  with the exception of ammonium which is
  positively charged NH4+1
• When there is more than one of a polyatomic ion
  in a compound it must be place in parentheses
  and the subscript put outside of the parentheses
• (NH4)2SO4 is the correct formula for ammonium
  sulfate.

				
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