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					Ionic and Covalent Bonding

     Chapter 4 – Section 2
        Pg. 116 - 122
                  Bonding
• Atoms with unfilled valence shells are
  considered unstable.
• Atoms will try to fill their outer shells by
  bonding with other atoms.
• The number of valence electrons will
  determine how many bonds the atom can
  form.
• Two types of bonds we will discuss:
  – Ionic bonds
  – Covalent bonds
                 Ions Review
• Ions are charged atoms (positive or negative).

• Ions are formed when atoms gain or lose
  electrons.

• Positive ions are called cations.
   – Formed when the atom loses electrons.


• Negative ions are call anions.
   – Formed when the atom gains electrons.
               Ionic Bonds
• Ionic bonds are formed between metals
  and non-metals.

• Ionic bonds are formed between
  oppositely charged atoms (ions).

• Ionic bonds are formed by the transfer of
  electrons.
  – One atom donates electrons to the other.
       Ionic Bonds (continued)
• In an ionic bond one atom will lose its electron(s)
  and the other will gain them.
   – Depends on the number of valence electrons.


• The transfer of electrons creates a positive ion
  and a negative ion.

• The opposite charges attract one another,
  causing a bond to form.

                   Bonding Animation
          Drawing Ionic Bonds
• We can illustrate ionic bonding using
  Lewis structures.
• 1 – Draw the Lewis structure for each
  element.
  – Ex:        Na             Cl
• 2 – Draw arrows to show the gain/loss of
  electrons
  Drawing Ionic Bonds (continued)
• 3 – Draw ion Lewis diagrams showing the
  new charge for each ion.
  – Ex:
• The chemical formula for the compound
  formed represents the ratio of negative
  ions to positive ions.
  – Ex: NaCl – for every 1 sodium ion, there is
    also 1 chlorine ion.
    Practice Drawing Ionic Bonds
Elements    Lewis     Ion Lewis   Formula
            Diagram   Diagram



Calcium
Flourine



Magnesium
Bromine
           Covalent Bonds
• Covalent bonds form between two non-
  metals.
• Covalent bonds are formed when atoms
  share electrons.
  – Both atoms need to gain electrons, so they
    share the electrons they have.
• Atoms can share more than one pair of
  electrons to create double and triple
  bonds.
     Covalent Bonds (continued)
• Atoms can share their electrons equally or unequally.

• When atoms share electrons equally it is called a non-polar
  bond.
   – Non-polar covalent bonds form between atoms of the same type. Ex:
     H2

• When atoms share electrons unequally it is called a polar
  covalent bond.
   – One atom pulls the electrons closer to itself.
   – The atom that pulls the electrons more gets a slightly negative
     charge.
   – The other atom gets a slightly positive charge.
       • Ex: Water molecule
                       Bonding Animation
          Drawing Covalent Bonds
• We can illustrate covalent bonding using
  Lewis structures.
• 1 – Draw a Lewis structure for each element.
  – Ex:        C              H
• 2 – Draw circles around the shared pair(s) of
  electrons.
  – Ex:
• 3 - Continue adding atoms until all atoms
  have a full valence shell.
  – Ex:
 Practice Drawing Covalent Bonds
Elements       Lewis      Formula
               Diagram

Hydrogen
Hydrogen

Carbon
Oxygen
     Ionic Vs. Covalent Bonds
      Ionic Bonds           Covalent Bonds
• Form when electrons   • Form when electrons
  are exchanged           are shared between
  between atoms.          atoms.
• Form between a        • Form between two
  metal and a non-        non-metals.
  metal.

    Both types of bonds result in all atoms
       having a full outer energy level.

				
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posted:11/23/2011
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