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TABLE 9.7
tion, and possibly a bloated feeling, nausea, vomiting, and body
Prefixes and element stem names electrolyte imbalance. For those who have become dependent,
DHMO withdrawal means certain death.”
Prefixes Stem Names
The above is part of a hoax that was recently circulated
Prefix Meaning Element Stem on the Internet. The truth is that dihydrogen monoxide is the
chemical name of H 2 O—water.
Mono- 1 Hydrogen Hydr-
Di- 2 Carbon Carb-
Tri- 3 Nitrogen Nitr-
Tetra- 4 Oxygen Ox-
COVALENT COMPOUND FORMULAS
Penta- 5 Fluorine Fluor-
The systematic name tells you the formula for a covalent com-
Hexa- 6 Phosphorus Phosph-
pound. The gas that dentists use as an anesthetic, for example,
Hepta- 7 Sulfur Sulf-
is dinitrogen monoxide. This tells you there are two nitrogen
Octa- 8 Chlorine Chlor-
atoms and one oxygen atom in the molecule, so the formula is
Nona- 9 Bromine Brom-
N 2 O. A different molecule composed of the very same elements
Deca- 10 Iodine Iod-
is nitrogen dioxide. Nitrogen dioxide is the pollutant responsible
for the brownish haze of smog. The formula for nitrogen diox-
Note: The a or o ending on the prefix is often dropped if the stem name begins with a
vowel, e.g., tetroxide, not tetraoxide. ide is NO 2 . Other examples of formulas from systematic names
are carbon dioxide (CO 2 ) and carbon tetrachloride (CCl 4 ).
Formulas of covalent compounds indicate a pattern of how
compounds must therefore provide a means of identifying dif-
many atoms of one element combine with atoms of another.
ferent compounds made of the same elements. This is accom-
Carbon, for example, combines with no more than two oxygen
plished by using a system of Greek prefixes (see Table 9.7). The
atoms to form carbon dioxide. Carbon combines with no more
rules are as follows:
than four chlorine atoms to form carbon tetrachloride. Electron
1. Th e first element in the formula is named first with a dot formulas show these two molecules as

prefix indicating the number of atoms if the number is O
Q
greater than 1. S ClS
O
O
O
C
Q
Q
Q
Q

2. The stem name of the second element in the formula is OSSCSSO O S ClS S ClS
O
Q

next. A prefix is used with the stem if two elements form S ClS
more than one compound. Th e suffi x -ide is again used to
indicate a compound of only two elements. Using a dash to represent bonding pairs, we have
For example, CO is carbon monoxide and CO 2 is carbon Cl
dioxide. The compound BF 3 is boron trifluoride and N 2 O 4 A
O P C P O ClOCOCl
is dinitrogen tetroxide. Knowing the formula and the prefix A
and stem information in Table 9.7, you can write the name of Cl
any covalent compound made up of two elements by ending
In both of these compounds, the carbon atom forms four
it with -ide. Conversely, the name will tell you the formula.
covalent bonds with another atom. The number of covalent
However, there are a few polyatomic ions with -ide endings
bonds that an atom can form is called its valence. Carbon has a
that are compounds made up of more than just two elements
valence of 4 and can form single, double, or triple bonds. Here
(hydroxide and cyanide). Compounds formed with ammo-
are the possibilities for a single carbon atom (combining ele-
nium will also have an -ide ending, and these are also made
ments not shown):
up of more than two elements.
A A
O C O O C P P C P O C q
A
Myths, Mistakes, & Misunderstandings
Hydrogen has only one unshared electron, so the hydrogen
Ban DHMO? atom has a valence of 1. Oxygen has a valence of 2 and nitrogen
has a valence of 3. Here are the possibilities for hydrogen, oxy-
“Dihydrogen monoxide (DHMO) is colorless, odorless, and
gen, and nitrogen:
tasteless, and it kills uncounted thousands of people every
year. Most of these deaths are caused by accidental inhalation H O O O O SO P
O
O
of DHMO, but the dangers do not end there. Prolonged expo- Q
sure to its solid form causes severe tissue damage. Symptoms Q Q
of DHMO ingestion can include excessive sweating and urina- O N O O N P SN q
A
244 CHAPTER 9 Chemical Bonds 9-16