Lewis Dot Structures for Bonding by hedongchenchen

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									Lewis Dot Structures for Bonding
                  Review
• What is bonding?
• Why does it occur?
• How do they form? (Explain difference
  between ionic and covalent
• What is bonding?
  – Attraction of valence electrons of one atom to the
    nucleus of another atom
• Why does it occur?
  – STABILITY!!!! Because of bonding, each element
    will obtain full valence/outer shell (8 e-)
• How do they occur
  – Ionic (metal and non metal)
     • Metal gives electrons to nonmetal
     • Atoms are then attracted, but DO NOT OVERLAP
           Covalent Bonding
• Two non metals SHARE a pair of electrons
• Called a molecule
• Shared electrons will allow both atoms to
  obtain the octet in valence shell
• Electrons will be shared equally between the
  two atoms
            How do they form?
• Overlap of orbitals is how the electrons are
  shared
• The overlap causes a pseudo octet in valence
  – Both atoms feel like they have an octet
• Two types of overlap
  – Sigma
  – pi
                Sigma bond
• Overlap of two s orbitals
• Share only one pair of electrons
• Called a single bond
                    Pi bond
•   Overlap of p orbitals
•   Sharing of two or three pairs of electrons
•   Share two pairs of electrons = double bond
•   Share three pairs of electrons = triple bond
Which bonds are stronger?? Shorter??
• The more electrons that are shared the
  stronger the bond will be.
  – Bond energy – energy required to break the bond
• The more electrons that are shared the
  tighter/shorter the bond will be

  – Single Weakest, longest
  – Double
  – Triple Strongest, shortest
 How can we represent these bonds?
• Lewis dot structures
   – How do we write these for individual atoms?
      • N? Cl?
      • Number of non-paired e- = number of bond possible



                      F F
  – Circled dots represent the shared electron pair
  – Other electron pairs are not involved in the bonding
  – Belong to one atom – nonbonding pair
            How do I do this???
• Step 1: Determine types of atom and how
  many you will need – i.e. the formula
  – PH3


• Step 2: Write Lewis dot notations for
  individual atoms
  – P? H?
• Step 3: Determine total number of valence
  electrons in compound
  – Add together the number of valence electrons for
    each element
           P: 1 x 5e- = 5e-
           H: 3 x 1e- = 3e-
                        8e-
• Step 4: Least electronegative element goes in
  center or element with most bonding sites
     Except: - Hydrogen NEVER in center
            - If carbon is present, it goes in the center
               H
           H P H
• Step 5: Place an electron pair between every
  element
                     H
                H P H
• Step 6: Add unshared pairs to all atoms until
  they have a full Octet (hydrogen should only
  have 2)
                  H
                H P H

• Step 7: Self check, number of electrons
  should equal match total number of valence
  electrons.
    Let’s do another example

• NI3
Lewis Dot for double and triples bonds
• Follow steps 1 – 7
• If there are too many electrons, the molecule
  may have double or even triple bonds.
• Step 8: Remove electron pairs until desired
  number of electrons is reached.
• Step 9: Some elements will no longer have an
  octet so we must move e- pairs to non-
  hydrogen bonds until all elements have an
  octet
        Examples
• CO2



• HCN

								
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