Chemistry Reference
In-Depth Information
bonding site, which fit together like pieces of a puzzle. When the individual
Lewis dot diagrams combine, each atom will look as if it has a complete
valence shell. Oxygen will act as though it has 8 valence electrons, like
neon, and hydrogen will act as if it has 2 valence electrons, like helium.
Notice that the number of hydrogen atoms that could bond with the oxy-
gen atom in this situation was dictated by the number of bonding sites avail-
able in each atom.
For our next example, let's look at how chlorine and carbon react to
form the molecular compound called carbon tetrachloride. As before, we
will begin by looking at the Lewis dot diagrams for the individual elements,
which are based on their individual electron configurations.
Each chlorine atom has 7 valence
electrons. In order to complete its octet,
each chlorine atom needs one more elec-
tron. It can either steal an additional elec-
tron to form the chloride (Cl
-
) ion, or it
can form one single covalent bond and
act as though it has a noble gas configu-
ration for part of the time.
There is, however, a problem with the Lewis dot diagram for the car-
bon atom as it appears in Figure 4-3c. Carbon is shown with only two lone
electrons, suggesting that it can only make two single covalent bonds. The
problem is that sharing two pairs of electrons with chlorine would not com-
plete its octet, and would leave it unstable, as shown in Figure 4-3d.
Lewis Dot Notations for
Carbon and Chlorine
C
Cl
Figure 4-3c
Experimental evidence shows that
carbon will react with chlorine in a 1:4
ratio, to form the compound called car-
bon tetrachloride (CCl
4
). You will recall
that the electron configuration for car-
bon is 1s
2
2s
2
2p
2
. The “2s” and “2p” elec-
trons of the carbon atom are said to form
hybrid orbitals of equal energy, allowing
them all to become bonding sites. This
allows each carbon atom to make four
single covalent bonds, two double cova-
lent bonds, or one triple and one single
covalent bond, any of which would result
in completing the carbon atom's octet.
Predicted Lewis Dot Notation
for a Compound Containing
Carbon and Chlorine
Cl
C Cl
Each chlorine atom appears to
have a complete octet, but the
carbon atom lacks the stability
of a noble gas.
Figure 4-3d
