Chapter 16: Covalent Bonding

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Chapter 16 Covalent Bonding

• A. Properties of Covalent Bonds/Compounds
• Sharing of electrons in a molecule (non-metals)
• Can be solids, liquids, or gases
• Have low melting points
• Relatively weak bonds
• Poor conductors of electricity
• Not very soluble in water

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• B. Diatomic Molecules
• Diatomic Molecules molecules that always go
  together in groups of 2 atoms
• - like Siamese twins
• - stable as a pair (they are never by
  themselves)
• - H2 O2 Br2 F2 I2 N2 Cl2

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• C. Formation of Covalent Bonds/Compounds
• Covalent bonds molecules (non-metals) share
  pairs of e to form a bond
• - 2 e 1 pair
• - therefore translates into
  to show a bond between atoms
• - goal stable octet of electrons (8
  e) around every atom
• - exceptions to the octet rule
  Hydrogen (2 e), Helium (2 e), Boron (6
  e), Phosphorus (10 e), and Sulfur (12
  e)

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• Sharing of electrons
• ex. H2 (H H)
• H? ?H ? HH ? H-H

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• Sharing of electrons (cont.)
• ex. Cl2 (14 val. e)
• ex. O2 (12 val. e)
• ex. N2 (10 val. e)

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• Sharing of electrons (cont.)
• ex. CO2 (16 val. e)
• ex. H2O (8 val. e)

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• Sharing of electrons (cont.)
• ex. CH4 (8 val. e)
• ex. CCl4 (32 val. e)

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• Sharing of electrons (cont.)
• ex. CO32 (24 val. e)
• Resonance when a molecule has more than
  one valid (or possible) Lewis dot diagram
• - all structures are correct and all
  occur simultaneously

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• D. VSEPR Theory
• Valence Shell Electron Pair Repulsion Theory
• VSEPR Theory valence shell electrons (in pairs)
  will repel one another to get into
  stable positions of different shapes and
  bond angles
• AX - uses 3 letters (A, X, E) to help determine
  the molecules geometric shape and angle
• Central atom (A) the atom in the center
  (the 1st atom, except H2O)
• Terminal atoms (X) atoms connected to the
  center atom
• Lone e pairs (E) the pairs of 2 e that is on
  the center atom

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• Unshared e pair - electrons that are not bonded
• - lone e pair () on the central
  atom
• Shared e pair electrons that are bonded ()
• Using your VSEPR sheet
• Draw Lewis dot diagram
• Find the AX
• Locate the geometric shape and bond angle
• Determine the polarity (polar or non-polar) of
  the bonds and the entire molecule
• Note 2 atom molecules do not have an AX , and
  its shape will be linear (180?)

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• VSEPR Sheet
• You will get this on any test/quiz!
• AX2E2 105? bent

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• Why is a water molecule bent?
• Its because of VSEPR!
• ex.

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• E. Polar vs. Non-polar
• Bond polarity and molecule polarity
• Polar bond electrons shared unevenly in a bond
• - electronegative difference between
  atoms in a bond
• - different elements across a bond
• ex.
• Non-polar bond electrons shared evenly in a
  bond
• - no electronegative difference
  between atoms in a bond
• - same element across a bond
  (diatomic molecules)
• ex. H-H or F-F

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• Polar molecule uneven molecule - not
  completely symmetrical
• ex.
• Non-polar molecule even molecule
• - dipoles cancel out
• - complete symmetrical
• ex.

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• F. Bond Energy, Strength, and Length
• The more bonds (triple vs. single), the stronger
  the bond is (more energy)
• The more bonds (the stronger the bonds are) the
  shorter the bond length is (atoms are closer
  across the bond)