Molecular Compounds

1
Molecular Compounds
2
Review

• Ionic compounds contain positive ions and
  negative ions.
• Positive ions are usually metal ions.
• Except for NH41.
• Negative ions are usually nonmetals or polyatomic
  ions.
• An ionic bond is the force that holds oppositely
  charged ions together.

3
Covalent Bonds

• Molecular compound held together by covalent
  bonds
• Covalent bond happens when atoms share
  electrons to reach octet.
• Non-metal non-metal
• Metalloid non-metal

4
Covalent Bonds
H
H
H
H
Electrons now belong to both atoms. Both H atoms
have 2 valence electrons (same as He)
5
Covalent Bonds
6
Covalent Bonds

• Every covalent bond involves 2 e-
• Sometimes atoms can form multiple bonds.
• Share more than 1 pair of e-.

7
Salts vs. Molecules

• Molecules exist as separate bundles of atoms.
• The forces between molecules are much weaker than
  the forces within molecules.
• Molecular compounds tend to melt and boil at much
  lower temperatures than ionic compounds.

8
Salts vs. Molecules
Weak forces between molecules.
Very strong forces between atoms.
Very strong forces between ions.
9
Salts vs. Molecules
Compound
Melting Point
Boiling Point
NaCl
801º C
1413º C
KBr
734º C
1435º C
Ionic Compounds (salts)
FeCl3
306º C
decomposes at 315º C
H2O
0º C
100º C
SO2
-75.5º C
-10º C
Covalent Compounds (molecules)
PCl3
-93.6º C
76.1º C