SCH 4U1
BONDING AND THE OCTET RULE
1)
Properties of compounds (eg. BP, solubility, hardness, etc.) are greatly
influenced by the polarity of the bond.
Eg.
- Br2 is a covalent bond and is non-polar. (There are no +/- poles.)
- O-H is a polar covalent bond and is described as being a polar
molecule. There is an unequal distribution of electron density in a neutral
water molecule.
- Na+ Cl- is an ionic bond and is very polar. (There is a distinct positive
pole and a distinct negative pole)
2)
Bonding is a continuum so the difference in electronegativity will
influence the type of bond that will occur.
electronegativity
difference
0
1
2
3
|__________|__________|__________|__
non-polar<-----
polar ---> <----- ionic ----->
covalent
3)
Like dissolves like. A non-polar substance will dissolve in a non-polar
substance - rubber and graphite from a pencil. A polar substance will
dissolve in a polar substance - table salt in water.
4)
Bonding will occur because of stability and this is governed by the
octet rule. Regardless whether an electron is being transferred (ionic BaCl2) or shared (covalent - NH3) a given atom wants to be surrounded by
eight electrons (or have a complete shell).
5)
Multiple bonding may occur in order to satisfy this requirement - Eg.
CO2 or C2H2 have double and triple bonds respectively.