Question 6.14: Draw the Lewis structures for carbon dioxide, CO2....

Table 1

STEP 1   Determine the arrangement of atoms. In CO_{2}, the central atom is C because there is only one C atom.
O         C        O

STEP 2   Determine the total number of valence electrons. We use the group number to determine the number of valence electrons for each of the atoms in the molecule.

Table 2

STEP 3   Attach each bonded atom to the central atom with a pair of electrons.

O\mathrm{:}C\mathrm{:}O       or      O \space — \space C \space — \space O

We use four valence electrons to attach the central C atom to two O atoms, which leaves 12 valence electrons.
STEP 4   Use the remaining electrons to complete octets, using multiple bonds if needed.
The 12 remaining electrons are placed as six lone pairs of electrons on the outside O atoms. However, this does not complete the octet of the C atom.

\mathrm {:}\overset{\mathrm {.~.}}{\underset{.~.}{O}} \mathrm {:}C\mathrm {:}\overset{\mathrm {.~.}}{\underset{.~.}{O}} \mathrm {:}        or        \mathrm {:}\overset{\mathrm {.~.}}{\underset{.~.}{O}} \space — \space C \space — \space  \overset{\mathrm {.~.}}{\underset{.~.}{O}} \mathrm {:}

To obtain an octet, the C atom must share pairs of electrons from each of the O atoms. When two bonding pairs occur between atoms, it is known as a double bond.