Covalent (Molecular) Compounds
When nonmetals bond to form compounds their valence shells
overlap and the valence electrons are shared between the atoms.
The resulting group of atoms is called a molecule.
The simplest compound of this type is H2 , a hydrogen molecule.
The Lewis structure for this molecule is:
+
This type of molecule is called a diatomic molecule. In nature
there are seven elements that exist as diatomic molecules.
hydrogen - H2 (gas)
nitrogen - N2
(gas)
oxygen - O2
(gas)
fluorine - F2
(gas)
chlorine - Cl2
(gas)
bromine - Br2
(liquid)
iodine - I2
(solid)
The atoms are more stable when bonded than by themselves
because the electrons are attracted to two positive nuclei. The
element name is used as the name of the diatomic molecule.
“Octet Rule or Rule of Eight”
• States that atoms lose, gain or share electrons in order to have a full
valence shell, which is the electron configuration of a noble gas.
Lewis Structure: Water
Oxygen bonds covalently with other nonmetals. In the example of
water, oxygen shares two electrons with two hydrogen atoms. This
fulfills the “rule of eight” for oxygen. Each hydrogen atom will have
two valence electrons. (Recall that hydrogen only has a 1s orbital and
can only have two electrons.)
Naming Molecular Compounds
• A system of prefixes is used to represent the number of
atoms of each type of element.
One Atom
mono -
Six Atoms
Two Atoms
di -
Seven Atoms hepta -
Three Atoms tri -
hexa -
Eight Atoms
octa -
Four Atoms
tetra -
Nine Atoms
nona -
Five Atoms
penta -
Ten Atoms
deca -
Rules When Naming Binary Molecular Compounds:
• First, check to see that the compound is made of nonmetals.
• Name the first element.
• Name the second element and change the ending to –ide.
• Add prefixes to indicate the number of atoms of
each type of element.
Name
Common Name
N2O
dinitrogen monoxide
laughing gas
NH3
nitrogen trihydride
ammonia
CH4
carbon tetrahydride
methane
Symbol
END