Chemistry NOTES
Chemical Nomenclature
Chemical Compounds
There are two main types of chemical compounds, molecular and ionic. Molecular
compounds are made of atoms which are tightly bound together. Generally, molecular
compounds are made from two or more nonmetallic atoms. Ionic compounds are made
of positive and negatively charged ions, which are held together with electrostatic
attractions. Cations, or positive ions, are formed when metal atoms lose electrons.
Anions, or negative ions, are formed when nonmetal atoms gain electrons. Ionic
compounds are generally made from metallic plus nonmetallic ions.
Monatomic Ions
The ionic charges of monatomic ions often can be determined by using the periodic table.
The formulas of monatomic ions are written as the element symbol followed by the
charge written as a superscript. Charges are written as the numerical value followed by
the + or – sign. If the numerical value of the charge is one, only the + or – is written.
Metals in Groups 1A, 2A, and 3A lose electrons when they form cations. Their ionic
charge is positive and numerically equal to the group number. Their names are the same
as the metal name (as in the sodium ion, Na+).
Group A nonmetals form anions, and their charge can be obtained by subtracting 8 from
the group number; the sign is negative. Their names end in –ide (as in oxide ion, O2-).
Nonmetals in Group 4A and Group O normally do not form ions.
1.
Name the following Group A ions. Determine how many electrons were lost
or gained by the atoms to form these ions.
a.
b.
c.
Al3+
Sr2+
S2 –
d.
e.
f.
Rb+
P3 –
Cs+
g.
h.
i.
Ba2+
Se2 –
I–
Many of the transition metals (Group B) form cations with more than one charge. This
is also a characteristic of the cations of tin and lead, the two metals of Group 4A.
(Exceptions: Ag forms only 1+ cations; Zn and Cd form only 2+ cations). There are two
methods of naming transition metal ions having a variable charge. In the Stock system
of naming, a Roman numeral in parentheses is used in the ion’s name to indicate the
numerical value of the charge. The Fe2+ ion is named the iron(II) ion. (There is no space
between the element name and the parenthesis.) In the classical system of naming, the
classical name of the element (such as ferr-, from ferrium, Latin for iron) is used as a root
word, and a suffix is used to indicate the charge. The root word is followed by the suffix
–ous to name the cation with the lower of the two ionic charges, and the suffix –ic is used
with the higher of the two ionic charges. The Fe2+ ion is named the ferrous ion and the
Fe3+ ion is named the ferric ion.
Formulas and Names of Common Metal Ions with More than One Ionic Charge
Formula
Cu+
Cu2+
Fe2+
Fe3+
*Hg22+
Hg2+
Pb2+
Pb4+
Sn2+
Sn4+
Cr2+
Cr3+
Mn2+
Mn3+
Co2+
Co3+
Stock Name
copper(I) ion
copper(II) ion
iron(II) ion
iron(III) ion
mercury(I) ion
mercury(II) ion
lead(II) ion
lead(IV) ion
tin(II) ion
tin(IV) ion
chromium(II) ion
chromium(III) ion
manganese(II) ion
manganese(III) ion
cobalt(II) ion
cobalt(III) ion
Classical Name
cuprous ion
cupric ion
ferrous ion
ferric ion
mercurous ion
mercuric ion
plumbous ion
plumbic ion
stannous ion
stannic ion
chromous ion
chromic ion
manganous ion
manganic ion
cobaltous ion
cobaltic ion
* A diatomic elemental ion
Reminder: The transition metals Ag, Zn, and Cd form ions with only one charge, so their
names do not include Roman numerals. You must remember their charges!
2.
Name the following ions. Use the Stock system, then using the classical
system, to name any transition metal ions:
a.
b.
c.
d.
K+
Mn2+
Mg2+
Pb4+
e.
f.
g.
h.
Cu+
Hg2+
Ga3+
F–
i.
j.
k.
l.
Li+
Sn2+
Zn2+
N3 –
Polyatomic Ions
Polyatomic ions are tightly bound groups of atoms that behave as a unit and carry a
charge. The ammonium ion is a polyatomic cation. The names of most polyatomic
anions end in either –ite or –ate. There are a few exceptions, including cyanide (CN-)
and hydroxide (OH-). If polyatomic anions containing oxygen exist as an –ite/-ate pair,
the charge on the pair is the same, and the –ite ending indicates one less oxygen atom
than the –ate ending. Nitrite is NO2 – and nitrate is NO3 –.
For a series of polyatomic anions containing oxygen (oxyanions) containing more than
two members, the ion with the largest number of oxygen atoms has the prefix per- and
the suffix –ate; the ion with the smallest number of oxygen atoms has the prefix hypoand the suffix -ite. The oxyanions containing chlorine are the most common examples:
ClO4- is the perchlorate ion
ClO3- is the chlorate ion
ClO2- is the chlorite ion
ClO- is the hypochlorite ion
Common Polyatomic Ions
1+ charge
/
formula, name /
NH4+, ammonium
Hg22+, mercury(I)
3- charge
/ 2- charge
/
formula, name / formula, name
/
PO43-, phosphate
SO42-, sulfate
PO33-, phosphite
SO32-, sulfite
3BO3 , borate
CO32-, carbonate
AsO33-, arsenate
C2O42-, oxalate
CrO42-, chromate
Cr2O72-, dichromate
HPO42-, hydrogen phosphate
O22-, peroxide
1- charge
formula, name
NO3-, nitrate
NO2-, nitrite
ClO4-, perchlorate
ClO3-, chlorate
ClO2-, chlorite
ClO-, hypochlorite
BrO3-, bromate
IO3-, iodate
C2H3O2-, acetate
MnO4-, permanganate
HSO4-, hydrogen sulfate
HCO3-, hydrogen carbonate
H2PO4-, dihydrogen phosphate
CN-, cyanide
OH-, hydroxide
Rule: PO’s, BO’s, and AsO’s are 3SO’s, CO’s, and CrO’s are 2NO’s, halO’s, and CHO, and are 1CN, OH, and MnO4 are 1NH4 is 1+
Ionic Compounds
Ionic compounds are generally made from metallic plus nonmetallic ions. Objects of
opposite electrical charges are attracted to each other.
When metals react with nonmetals, they do so in a way to create a neutral compound.
The total number of positive charges on the cations must equal the total number of
negative charges on the anions. The net charge on any compound is zero. Subscripts
are used to indicate the numbers of atoms or ions of each type in a compound.
3.
For each of the following ionic compounds, tell what ions are present and give
their relative number.
a. MgBr2
b. Li2CO3
c. Fe2(SO4)3
d. NaF
We can predict the formula of an ionic compound because the number of positive charges
carried by the cation (or cations) must equal the total number of negative charges carried
by the anion (or anions). In writing the formulas of ionic compounds, the symbol of the
cation is always given first, followed by the symbol of the anion. Parentheses are used to
set off a polyatomic ion that appears more than once in the formula.
When naming ionic compounds, the positive ion name is given first followed by the
name of the negative ion. Names of compounds composed of ions are built from the
names of the ions involved.
4.
What ionic compounds form when you combine an aluminum ion with
a. a bromide ion,
b. an oxide ion,
c. a nitrate ion
5.
Chromium is a transition metal and so can form ions with at least two different
charges.
a. Write the formulas of the compounds formed between chromium and
sulfur.
b. Name the compounds formed.
Naming Binary Compounds of the Nonmetals
Another type of compound, a molecular compound, is made from the combination of
two nonmetals. These “two element” or binary compounds can be named in a
systematic way. Almost all of the binary, nonmetal compounds you will see have at least
one element from Groups 6A or 7A. This element is always listed second in the formula
and is named second with the –ide suffix. The numbers of atoms of a given atom in the
compound is designated with a prefix.
Prefixes Used in Naming Molecular Compounds
1
2
3
4
5
mono- (dropped if first)
ditritetrapenta-
6
7
8
9
10
hexaheptaoctanonadeca-
Many of the binary molecular compounds were discovered years ago and have common
names. These names simply must be learned as in H2O (water) and NH3 (ammonia).
Another common compound you should know is CH4 (methane).
At this point, you cannot predict the formula of a binary, nonmetal compound the way
you can predict the formulas of ionic compounds.
6.
Name the following molecular compounds:
a.
NH3
c.
SF4
b.
P2O5
d.
O2F2
Acid Nomenclature
Acids are compounds that produce hydrogen ions when dissolved in water. When
naming acids and writing their formulas, you can consider them to be combinations of
anions connected to as many H+ ions as are needed to make the molecule electrically
neutral. The chemical formulas of acids are of the general form HX, where X is a
monatomic or polyatomic anion.
1.
When the name of the anion ends in –ide, the acid name begins with the
prefix hydro-. The stem of the anion has the suffix –ic and is followed by the
word acid. Thus the anion Cl- (chloride) forms hydrochloric acid (HCl).
2.
When the anion name ends in –ite, the acid name is the stem of the anion
with the suffix –ous, followed by the word acid. Thus the anion SO32- (sulfite)
forms sulfurous acid (H2SO3).
3.
When the anion name ends in –ate, the acid name is the stem of the anion
with the suffix –ic, followed by the word acid. Thus the anion NO3- (nitrate)
forms nitric acid (HNO3).
7.
Name the following compounds as acids.
a. HClO
c. H3PO4
b. HCN
d. HF
8.
Write the formulas for these acids.
a.
hydrobromic acid
b.
sulfuric acid