Naming Covalent/ Molecular
Compounds
Naming Covalent Compounds
Hydrogen compounds are handled differently and will be
looked at first.
Nomenclature:
1)
Name the hydrogen that appears in the formula.
2)
Name the second element that appears in the formula,
changing its ending to –ide. (Similar to ionic compounds)
Examples:
HCl
HI
hydrogen chloride
hydrogen iodide
Covalent Bonds use prefixes to
indicate the number of atoms
involved in the compounds
1= mono
2 = di
3 = tri
4 = tetra
5 = penta
6 = hexa
7= hepta
8 = octa
9 = nona
10 = deca
RULES
1- The name of the first element does not get
changed, only a prefix is added if it is more
than one.
Ex: Trisulfur tetrafluoride
S3F4
2- The second element gets a different
ending, as well as a prefix.
Ex : phosphorus trichloride PCl3
(NOT: phosphorus trichlorine)
RULES continued..
3- If the first element in the compound is single you
do not write mono:
ex. CO2 - carbon dioxide
(NOT monocarbon dioxide)
4- If the element’s name starts with a vowel, and
the prefix ends with a vowel, you can drop the
last vowel on the prefix:
ex. S5O10 - pentasulfur decoxide
(NOT pentasulfur decaoxide)
RULES continued..
5- Covalent compounds do not get
simplified. Name the compound exactly as
you see it:
Ex. H2F2 = dihydrogen difluoride
(NOT hydrogen monofluoride HF)
Naming Covalent Compounds
What is the name of SO3?
STEP 1 The first nonmetal is S sulfur.
STEP 2 The second nonmetal is O, named oxide.
STEP 3 The subscript 3 of O is shown as the prefix tri.
SO3 → sulfur trioxide
The subscript 1(for S) or mono is understood.
7
Naming Covalent Compounds
(Continued)
Name P4S3
STEP 1 The first nonmetal P is phosphorus.
STEP 2 The second nonmetal S is sulfide.
STEP 3 The subscript 4 of P is shown as tetra.
The subscript 3 of O is shown as tri.
P4S3 → tetraphosphorus trisulfide
8
Names of Covalent
Compounds
Remember Prefixes are used
 in the names of covalent compounds
 because two nonmetals can form two or more
different compounds
Examples of compounds of N and O:
NO
nitrogen oxide
NO2
nitrogen dioxide
N2O
dinitrogen oxide
N2O4
dinitrogen tetroxide
N2O5
dinitrogen pentoxide
9
Learning Check
Select the correct name for each compound.
A. SiCl4
1) silicon chloride
2) tetrasilicon chloride
3) silicon tetrachloride
B. P2O5
1) phosphorus oxide
2) phosphorus pentoxide
3) diphosphorus pentoxide
C. Cl2O7
1) dichlorine heptoxide
2) dichlorine oxide
3) chlorine heptoxide
10
Solution
Select the correct name for each compound.
A. SiCl4
3) silicon tetrachloride
B. P2O5
3) diphosphorus pentoxide
C. Cl2O7
1) dichlorine heptoxide
11
Learning Check
Write the correct formula for each of the following:
A. phosphorus pentachloride
B. dinitrogen trioxide
C. sulfur hexafluoride
12
Solution
Write the correct formula for each of the following:
A. phosphorus pentachloride
1P
penta = 5Cl
PCl5
B. dinitrogen trioxide
di = 2N
tri = 3 O
N2O3
C. sulfur hexafluoride
1S
hexa = 6F
SF6
13
TRY THESE:
a) Diphosphorus pentoxide
b) Nitrogen monoxide
c) Xenon hexafluoride
d) Tetrarsenic decoxide
More Examples
a) SiO2
b) N2S5
c)P4O10
d)BrCl6
Formulas, Names and Uses of
Some Covalent Compounds
16
Learning Check
Write the name of each covalent compound.
CO
_____________________
CO2
_____________________
PCl3
_____________________
CCl4
_____________________
N2O
_____________________
17
Solution
Write the name of each covalent compound.
CO
carbon monoxide
CO2
carbon dioxide
PCl3
phosphorus trichloride
CCl4
carbon tetrachloride
N2O
dinitrogen oxide
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Review of Covalent Compounds
HI
hydrogen iodide
NF3
nitrogen trifluoride
SO2
sulfur dioxide
N2Cl4
dinitrogen tetrachloride
NO2
nitrogen dioxide
N2O
dinitrogen monoxide
Ionic and Covalent
Identify each compound as ionic or covalent, and give
its correct name.
A. SO2
B. BaCl2
C. (NH4)3PO4
D. Cu2CO3
E. N2O4
20
Solution
Identify each compound as ionic or covalent, and give
its correct name.
A. SO2
covalent; sulfur dioxide
B. BaCl2
ionic; barium chloride
C. (NH4)3PO4
ionic; ammonium phosphate
D. Cu2CO3
ionic; copper(I) carbonate
E. N2O4
covalent; dinitrogen tetroxide
21
Learning Check
Name the following compounds:
A. Ca3(PO4)2
B. FeBr3
C. SCl2
D. Cl2O
22
Solution
Name the following compounds:
A. Ca3(PO4)2 ionic
Ca2+, PO43− calcium phosphate
B. FeBr3
ionic
Fe3+, Br −
iron(III) bromide
C. SCl2
covalent
1S, 2Cl
sulfur dichloride
D. Cl2O
covalent
2Cl, 1 O
dichlorine oxide
23
Homework
Page 249
Problems: 14, 15, 16 and 17
Page 274
Problems: 93, 94 and 95 (a-c)