Chemistry

1
Chemistry

• Chapter 9
• 9.1/9.2 Notes Part 2

2
Review

• Covalent Bonds
• Sharing of valence electrons
• Still atoms are trying to meet the octet rule
• of unpaired valence electrons decides how many
  bonds an atom can make
• Use electron dot structures to see how many
  unpaired electrons there are in an atom
• Bonds can be single, double, or triple

3
Single Bonds

• One shared pair of electrons
• Total of 2 e- in the bond
• Also called a sigma bond
• It just refers to the fact that there is a direct
  overlap between the outer energy levels of the
  atoms that are sharing e-

4
Multiple Bonds

• Double Bond
• 2 shared pair
• 4 e- total
• 1 sigma
• 1 pi
• Triple Bond
• 3 shared, 6 e-
• 1 sigma
• 2 Pi (parallel overlap)

Double bond Red in the center sigma Green
Pi (above below)
5
Strength of Bonds

• Bond Length
• The closer the nuclei are, the stronger the bond
• More shared pair closer the nuclei are
• Bond Dissociation Energy
• Amount of energy it takes to break a covalent
  bond
• As bond length decreases, the bond dissociation
  energy increases

6
Covalent Compounds

• Properties
• Nonconductors
• Low melting
• Low boiling point
• Mostly gas at room temp
• Solids are soft and brittle

7
Covalent Network Solids

• Graphite V. Diamond
• (allotropes)
• Covalent Network Solids
• Examples diamond and Quartz
• Covalently bonded in a crystal lattice (like an
  ionic compound) - a continuously bonded structure
• Hard, rigid
• High melting and boiling points
• nonconductors

8
Lewis Structures

• Electron diagrams of multiple atoms to show how
  they are arranged in molecules
• Ex. H2 H2O Ammonia
• Methane O2 CO2