Part III:
NAMING BINARY
COVALENT
COMPOUNDS
1
Essential Questions:


How can we decipher the name of covalent
compounds from their formulas?
And how can we figure out the formulas from
their names?
Naming Covalent Compounds
Note: We are just dealing with binary
compounds – which are compounds with
only two types of atoms.
They have two word names.
3
Guide to Naming Covalent
Compounds with Two Nonmetals
4

The first word corresponds to the
first element in the formula – as it
appears on the periodic table
5

The second word corresponds to the
second element in the formula

Use the root of its name from the
periodic table and add the suffix –ide
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
For the first element:

Remember that the # of atoms is given
by a subscript

ONLY add a prefix if there is more than
one atom. (never write mono- on the
first element)

For the second element:



ALWAYS add a prefix to the word to tell how
many are present (even if there’s only one)
Drop “o” or “a” at the end of a prefix when
the word following the prefix is oxide
(monoxide, pentoxide) but do not drop “i”
Never drop anything at the end of a prefix
when the word following the prefix is iodide
Roots of Nonmetals
H = hydrN = nitrO = oxSe = selenCl = chlorI = iod-
C = carbP = phosphS = sulfF = fluorBr = brom-
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Prefixes
1 =mono2 = di3 = tri4 = tetra5 = penta-
6 = hexa7 = hepta8 = octa9 = nona10 = deca-
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Exceptions to the Rule

Some important exceptions to this naming
scheme occur because the compounds were
originally named before the methodical
naming scheme above became
widespread. Today, these names are so
common that they're officially recognized:




H2O = water
NH3 = ammonia
CH4 = methane
Many others, particularly for organic molecules
and acids
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Example

Name the molecular compound that has the formula
S 2 O7




There are 2 sulfur atoms, so add the prefix diThe first element is named first, using the unchanged
element name: S = sulfur
There are 7 oxygen atoms, so add the prefix heptaThe second element’s root is then written with the suffix ide: O = ox- plus -ide = oxide
The
complete name is disulfur heptoxide
(a in hepta- is dropped before the vowel o
in oxide)
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Another Example

Name the molecular compound that has the formula
P 4 S3




There are 4 phosphorus atoms, so add the prefix tetraThe first element is named first, using the unchanged
element name: P = phosphorus
There are 3 sulfur atoms, so add the prefix triThe second element’s root is then written with the suffix ide: S = sulf- plus -ide = sulfide
The complete name is
tetraphosphorus trisulfide
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A Few More Examples
P2O5
CO
CF4
diphosphorus pentoxide, two
phosphorus atoms and five
oxygen atoms
carbon monoxide (need the
"mono-" because there's
only one oxygen atom)
carbon tetrafluoride,
because there's one carbon
atom and four fluorine atoms
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Try these on your own!
ClF
ClF5
BCl3
SF6
Cl2O
IF7
NI3
P4O10
B5H9
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Check your answers
ClF – chlorine monofluoride
ClF5 – chlorine pentafluoride
BCl3 – boron trichloride
SF6 – sulfur hexafluoride
Cl2O – dichlorine monoxide
IF7 – iodine heptafluoride
NI3 – nitrogen triiodine
P4O10 – tetraphosphorous decoxide
B5H9 – pentaboron nonahydride
Practice Writing Formulas
Phosphorus Trioxide
Dinitrogen Pentacarbide
Tellurium Noniodide
Carbon Monoxide
Selenium Heptaflouride
Tetraphosphorous Decoxide
Arsenic Hexabromide
Silicon Dichloride
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Check your answers
S2F10
 OF2
 N2O3
 P4S7
 CS2
 XeF2


ICl3

PO3

N2C5

TeI9

SeF7

AsBr6
Naming Molecular Compound Answers
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Carbon dioxide
Carbon monoxide
Sulfur dioxide
Sulfur trioxide
Dinitrogen monoxide
Nitrogen monoxide
Dinitrogen trioxide
Nitrogen dioxide
Dinitrogen tetroxide
Dinitrogen pentoxide
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
Phosphorous trichloride
Phosphorous
pentachloride
Nitrogen trihydride
Sulfur hexachloride
Diphosphourous pentoxide
Carbon tetrachloride
Silicon dioxide
Carbon disulfide
Oxygen difluoride
Phosphorous tribromide