Naming Compounds
and Writing Formulas
Naming Compounds
The chemical formula represents the composition of
each molecule.
In writing the chemical formula, in almost all cases
the element farthest to the left of the periodic table is
written first.
So for example the chemical formula of a compound
that contains one sulfur atom and six fluorine atoms
is SF6.
If the two elements are in the same period, the
symbol of the element of that is lower in the group
(i.e. heavier) is written first e.g. IF3.
Naming Ionic Compounds
Ionic compounds are combinations of positive
and negative ions.
In writing the chemical formula the positive ion is
written first, It is then followed by the name of the
negative ion.
Monatomic anions end in ide. Special endings
apply for polyatomic ions
Examples
NaCl Sodium chloride
BaF2 Barium Fluoride
ZnO Zinc Oxide
Writing Formulas for Ionic
Compounds
Write the positive ion (cation) first, then the
negative ion.
The positive charges must balance the negative
charges.
Use subscripts to show how many times each
ion must appear in order for the charges to
balance. A subscript is not used if the ion
appears only once
Use parenthesis around polyatomic ions that
appear more than once in the formula
Examples
1.
2.
3.
4.
5.
6.
7.
8.
9.
Na+
Zn2+
K+
Ca2+
Fe2+
Fe3+
Ca2 +
NH4+
NH4+
and Cland Brand OHand OHand SO42and SO42and PO43and Cland CO32-
= NaCl
= ZnBr2
= KOH
= Ca(OH)2
= FeSO4
= Fe2(SO4) 3
= Ca3(PO4)2
= NH4Cl
= (NH4)2CO3
Names of Polyatomic Ions
with Oxygen
Polyatomic ions
usually contain
oxygen in addition
to another element.
Normally they have
a negative charge.
They end in either
"ate" or "ite"
depending on the
number of oxygen
atoms present.
ClO-
hypochlorite
ClO2ClO3-
chlorite
chlorate
ClO4-
perchlorate
NO2-
Nitrite
NO3-
Nitrate
PO33-
phosphite
PO43-
phosphate
SO32SO42-
sulfite
sulfate
Polyatomic Ion -- Exceptions
Most polyatomic ions contain oxygen
Their names end in “ite” or “ate”.
There are several exceptions
OHCNSCN-
hydroxide
cyanide
thiocyanate
Transition Metal Cations
1.
2.
3.
4.
When an element can form more than one cation a
Roman numeral is used to distinguish the oxidation
state of the compound.
Metals not in group I, II, and III are common elements with
more than one cation. (Exceptions: silver, zinc, and
cadmium)
Examples
PbSO4 = lead (II) sulfate
This compound is formed
from Pb2+ and SO42Pb(SO4)2 = lead (IV) sulfate This compound is formed
from Pb4+ and SO42Fe(OH)2 = iron (II) hydroxide This compound is
formed from Fe2+ and OHFe(OH)3 = iron (III) hydroxide This compound is
formed from Fe3+ and OH-
Molecular compounds
• Two nonmetals or nonmetal +
metalloid
• element further left in periodic table
is 1st
• element closest to bottom of group is
1st
• use prefixes to indicate number of
each kind of atom
• Add prefix to first element name to
show how many of that element are
present. (omit ‘mono’)
• Add prefix to stem of last element
name plus “-ide”
2.7
Naming Covalent Compounds
Examples:
SF6 – sulfur hexafluoride
P4O10 – tetraphosphorous decoxide
CO – carbon monoxide
CO2 – carbon dioxide
Binary compounds of Hydrogen
The binary compounds of hydrogen are
special cases. They were discovered before
a convention was adopted and hence their
original names have stayed.
Water (H2O ) is not called dihydrogen monoxide
Hydrogen forms binary compounds with almost all nonmetals except the noble gases.
Examples
HF - hydrogen fluoride
HCl - hydrogen chloride
H2S - hydrogen sulfide
Molecular Compounds
HI
hydrogen iodide
NF3
nitrogen trifluoride
SO2
sulfur dioxide
N2Cl4
dinitrogen tetrachloride
NO2
nitrogen dioxide
N2O
dinitrogen monoxide
TOXIC!
Laughing Gas
2.7
An acid can be defined as a substance that yields
hydrogen ions (H+) when dissolved in water.
HCl
•Pure substance, hydrogen chloride
•Dissolved in water (H+ Cl-), hydrochloric acid
An oxoacid is an acid that contains hydrogen,
oxygen, and another element.
HNO3 (aq)
nitric acid
H2CO3 (aq)
carbonic acid
H2SO4 (aq)
sulfuric acid
HNO3
2.7
Naming Acids
Anion ending
Acid Name
-ide
hydro______ic acid
-ate
___________ic acid
-ous
___________ous acid
2.7
Acids
When many hydrogen compounds are dissolve in
water they take on the form of an acid. Special rules
apply to acids. The “ite” suffix becomes “ous” and
the “ate” suffix becomes “ic”
HCl
Hydrochloric Acid
Cl-
Chloride
HNO2
Nitrous Acid
NO2-
Nitrite
HNO3
Nitric Acid
NO3-
Nitrate
H2SO3
Sulfurous Acid
SO32-
Sulfite
H2SO4
Sulfuric Acid
SO42-
Sulfate
H3PO3
Phosphorous Acid
PO33-
Phosphite
H3PO4
Phosphoric Acid
PO43-
Phosphate
H2CO3
Carbonic Acid
CO32-
Carbonate
Diatomic Molecules
Certain elements
exist as diatomic
molecules in nature
H2
Hydrogen
N2
Nitrogen
F2
Fluorine
O2 Oxygen
I2
Iodine
Cl2 Chlorine
Br2 Bromine