12-9-15
¡ W hat are the seven diatomic molecules in the
periodic table? How can you easily remember
them?
PRACTICE PROBLEM
Draw the Lewis structures (dot diagrams) for
carbon dioxide, CO 2 :
1. First draw the dot
structures of the atoms:
2. Make single bonds to
connect atoms:
3. If atoms not octets,
make multiple bonds:
STRENGTH OF COVALENT BONDS
¡ S trength of covalent bonds can vary.
§ Depends on distance between bonded atoms.
§ In general, shorter bond length, higher bond strength.
¡ C onsider halogen diatomic molecules:
§ Atomic size trend:
F < Cl < Br < I
§ Bond length trend:
F 2 < Cl 2 < Br 2 < I 2
§ Bond strength trend: F 2 > Cl 2 > Br 2 > I 2
¡ M ultiple bonds make bond lengths shorter.
STRENGTH OF COVALENT BONDS
¡ D ouble bonds shorter length than single
bonds, and triple bonds shorter than double.
¡ C onsider F 2 (single bond), O 2 (double bond),
and N 2 (triple bond).
§ Bond length trend:
N2 < O2 < F2
§ Bond strength trend: N 2 > O 2 > F 2
**Double and triple bonds are very strong!
¡ E nergy required to break a specific covalent
bond called bond dissociation energy.
NAMING BINARY MOLECULES
¡ N omenclature for binary molecules used to
name molecules.
¡ R ules:
1.  The first element in the formula is always named
first, using the entire element name.
2.  The second element in the formula is named using
the root of the element and adding the suffix –ide.
3.  Prefixes are used to indicate the number of atoms
of each type that are present in the compound.
NAMING BINARY MOLECULES
¡ Table 9-1 Prefixes in Covalent Compounds
No. of
atoms
Prefix
No. of
atoms
Prefix
1
2
3
4
5
monoditritetrapenta-
6
7
8
9
10
hexaheptaoctanonadeca-
NAMING BINARY MOLECULES
¡ N ever use mono- prefix for first element if just
one.
¡ S ome molecules known by common names
§ E x. H 2 0, dihydrogen monoxide (water)
NH 3 , nitrogen trihydride (ammonia)
N 2 O, dinitrogen monoxide (nitrous oxide)
PRACTICE PROBLEMS
a.
b.
c.
d.
e.
CCl 4
As 2 O 3
CO
SO 2
NF 3
carbon tetrachloride
diarsenic trioxide
carbon monoxide
sulfur dioxide
nitrogen trifluoride
( P G . 24 9 )