Covalent Bonding

1
Covalent Bonding

• Chapter 8
• p. 239-271

2
Covalent Bonding (non-metal non-metal)sharing
electrons (P. 267-268)

• Polar Covalent Bonding
• Atoms have different electronegativities
• Difference in electronegativity is 0.4 - 1.7
• Non-polar Covalent Bonding
• Atoms with the same electronegativity (like the 7
  diatomic molecules)
• Ionic bonding (metal non-metal)
• Atoms have different electronegativities
• Difference in electronegativity is gt 1.7

3
Types of Covalent Bondsp. 244-245

• Single Bonds
• 1 Sigma bond 1 pair of electrons is shared
  between 2 atoms
• Double Bonds
• 1 Sigma 1 Pi bond -2 pairs of electrons are
  shared between 2 atoms
• Triple Bonds
• 1 Sigma bond 2 Pi bonds - 3 pairs of electrons
  are shared between 2 atoms

4
Length p. 246 Strength

• Single bonds are the longest
• Double bonds are medium length
• Triple bonds are the shortest

• Single bonds are the weakest
• Double bonds are medium strong
• Triple bonds are the strongest

5
Bond Energyp. 247

• Bond Dissociation Energy (always )
• Is the energy required to break a covalent bond
• When bonds form energy is released
• Energy must be added to break a bond

• Chemical Potential Energy is the sum of all bond
  dissociation energies

6
Energy Changep. 247

• Endothermic Reaction
• More energy is required to break the bonds in the
  reactants than is released when the new bonds
  form in the products.
• Energy debt
• Heat absorbed

• Exothermic Reaction
• More energy is released when bonds form in the
  products than when bonds are broken in the
  reactants
• Energy surplus
• Heat released

7
You Should Be Able To(You dont have to draw
resonance structures)

• Draw Lewis Dot Structures
• Show bonding pairs (with lines) lone pairs
  using dots or lines
• Each electron 1 dot
• 2 dots 1 line
• Draw Structural Formulas
• Show only bonding pairs with lines
• For any compound that follows the octet rule

8
Naming Covalent Compounds

• Answer p. 249 14-18
• Covalent compounds occur between 2 non-metals
• Use prefixes to determine the number of atoms of
  each element
• You do not have to name acids for this test.
• Prefixes will be written on the board

9
Naming Covalent CompoundsAnswer below p. 251
25-29
10
And the answers are
11
VSEPR Model p. 261-264

• Linear
• Trigonal Planar
• Tetrahedral
• Trigonal Pyramidal
• Bent
• Trigonal Bipyramidal
• Octahedral

• 2 bonds, 0 lone pairs
• 3 bonds, 0 lone pairs
• 4 bonds, 0 lone pairs
• 3 bonds, 1 lone pair
• 2 bonds, 2 lone pairs
• 5 bonds, 0 lone pairs
• (violates octet rule)
• 6 bonds, 0 lone pairs
• (violates octet rule)

12
Electronegativity Electron Affinity

• How tightly an atom can hold its electrons
• Fluorine (F) is the most electronegative
• Francium (Fr) is the least electronegative
• See p. 265 for a table of electronegativity values

• Tendency of an atom to accept an electron
• So electronegativity and electron affinity are
  different sides of the same coin

13
Polar Covalent Bondsp. 267-268

• Electrons are shared unequally
• Like a tug of war when one team is winning
• A dipole is created so that one part of the
  molecule is positive and the other is negative
• Therefore polar molecules align w/ an electric
  field
• Polar molecules only dissolve in other polar
  molecules

14
Properties of Covalent Compoundsp. 269-270

• Covalent compounds are held together by
  relatively weak intermolecular forces
• Therefore they have low melting and boiling
  points
• They also tend to exist as gases at room
  temperature
• Covalent network solids such as diamonds and
  quartz are very hard (unlike other covalent
  compounds)