» Binary molecular compounds
˃ Composed of two nonmetal elements
» No ions are present, just molecules, therefore
ionic charge cannot be used to write names or
formulas
» If we named molecular compounds as though
they were ionic compounds there would be no
way to differentiate between two or more
compounds with the same elements in different
ratios.
» We use prefixes in the name of binary
molecular compounds to differentiate between
compounds with different amounts of the same
elements.
» The prefixes tell us how much of each element
are present in 1 molecules of the compound
Table 9.4 Prefixes Used in Naming Binary Molecular Compounds
Prefix
Mono-
Di-
Tri-
Tetra-
Penta-
Hexa-
Hepta-
Octa-
Nona-
Deca-
#
1
2
3
4
5
6
7
8
9
10
» Confirm that the compound is a binary molecular
compound
» The name must identify the elements in the
molecule and the number of each atom
» Use prefixes to indicate the number of atoms
» If there is only 1 atom of the first element, do not
use a prefix (OMIT MONO-)
» The second element should always have a prefix.
» The central atom is generally written first.
» The suffix of the 2nd element will always be –ide.
» Examples
˃
˃
˃
˃
CO2  carbon monoxide
N2O  dinitrogen monoxide
Cl2O8 <-- dichlorine octoxide
SF6  sulfur hexafluoride
» To write the formula of a binary molecular
compound:
˃ Use the prefix in the name to tell you the subscript of each element in
the formula .
˃ Write the correct symbols for the two elements with the appropriate
subscripts.
Examples
Silicon carbide  there are no prefixes therefore there is 1 of each atom
in 1 molecule of the compound
SiC
Dinitrogen tetroxide  di = 2, tetra = 4
N2O4
» Acid – a compound that contains one or more
hydrogen atoms and produces H+ when dissolved in
water
» To name an acid:
˃ Think of the components of an acid as an anion and as
many hydrogen ions that are needed to balance the
charge of the anion. (you are making the molecule
electrically neutral.)
» the general form of the chemical formula of an acid
is HnX
» n = the number of hydrogen ions combined with
the anion
» X = a monatomic or polyatomic anion
» (aq) must appear after the formula to be named
as an acid
» Study these examples, and determine the rules
for naming acids:
Hint: relate the name of the anion, to the name of the
acid.
HCl (aq)
hydrochloric acid
HI(aq)
hydroiodic acid
H3PO4 (aq)
phosphoric acid
H2SO4 (aq)
sulfuric acid
HNO3 (aq)
nitric acid
HNO2 (aq)
nitrous acid
HClO (aq)
hypochlorous acid
H2Se (aq)
hydroselenic acid
H2S (aq)
hydrosulfuric acid
HC2H3O2 (aq)
acetic acid
» Two types of acids:
polyatomic anions
˃ _________ -ic acid (anion ends in –ate)
˃ _________ -ous acid (anion ends in –ite)
monatomic anions
˃ hydro_________ -ic acid
» The root of the anion name goes in the blank
To write the formula for an acid, use the naming rules
in reverse.
» Bases: A group of ionic compounds, that
produce OH- ions when dissolved in water.
» Name them like any other ionic compound.
Look back at the previous packet for naming
ionic compounds.
» Hydrated compounds are ionic compounds that
have water molecules “trapped” within the
crystal structure
» BaCl2 . 2H2O
The “dot” does not mean multiply! It is just a
symbol that connects the water molecules to the
ionic formula unit.
» Name the ionic piece, then use a prefix in front
of the word “hydrate” to complete the name.
» BaCl2 . 2H2O
barium chloride dihydrate
» We know that  compounds form in
predictable ways
» Mass measurements were used to deduce this
fact
» In samples of any chemical compound, the masses
of the elements are always in the same proportions
» In a sample of NaCl there is a fixed mass ratio of
sodium to chlorine.
» 39 g of Na and 61 g of Cl in a 100 g sample of NaCl.
» This reduces to a Na:Cl ratio of 0.639 : 1.
» This ratio is observed, no matter the size of the
sample. This empirical fact led to the conclusion
that if mass ratios are fixed, then atom ratios must
be fixed, also.
» This law deals with compounds that form in
more than one type of ratio.
» Can you think of any examples of this?
» Lead forms two compounds with oxygen?
Compound A
2.98 g Pb
0.461 g O
Compound B
9.89 g Pb
0.763 g O
Calculate the Pb:O ratio for each sample.
Compound A: 6.46:1 Compound B: 12.96:1
» The mass ratios of Pb are 6.46 : 12.96, or 1: 2, in the
two compounds.
» Whenever a compound of 2 elements forms in
multiple ratios, a whole-number ratio of masses is
observed.
» If the masses increase in whole-number ratios, then the
atoms must increase in whole-number ratios as well.
PbO2 and PbO4 are the two formulas. Which one is
compound A?
˃ Answer PbO4