CHEMICAL COMPOUNDS - VOCABULARY
COVALENT COMPOUND
A compound that has only covalent bonds between atoms of which it is made. The covalent
bond results from sharing valence electrons between two atoms. The representative unit of a
covalent compound is usually a molecule.
IONIC COMPOUND
A compound that is built of monatomic or polyatomic ions of opposite charges. The bonds
between ions of opposite charges are called ionic bonds. Many, but not all ionic compounds
contain a metallic element. The representative unit of an ionic compound is always a formula
unit. There no molecules in ionic compounds. Ions per se are not compounds.
FORMULA UNIT
The smallest combination of atoms or ions that correctly represents the ratio in which they are
combined in a chemical compound. Formula unit is a more general term than a molecule.
ORGANIC COMPOUND
A compound that is built of atoms of carbon and other elements (most commonly, hydrogen,
nitrogen, oxygen, sulfur, and halogens) except for carbon monoxide, carbon dioxide, carbonic
acid, carbonates, and hydrogen carbonates. If there is no carbon present, a compound is
certainly inorganic. The simplest organic compound is CH4, methane.
BINARY COMPOUND
Ionic or covalent compound that is made of atoms of two different elements. Examples:
MgCl2; Al2O3; HCl; H2O; CH4.
DIATOMIC MOLECULE
A molecule that is built of exactly two atoms either of the same element or of two different
elements. Examples: O2; N2; CO; HF.
MONATOMIC ION
A single atom that lost or gained one or more electrons as compared to the neutral atom of the
same element. The electric charge must be indicted when a formula of it is written unless the ion
is combined with another ion in the formula of an ionic compound. Examples: Na+; Fe3+; Br–; S2–.
POLYATOMIC ION
A group of atoms either of the same element or different elements held together by covalent
bonds like atoms in a molecule, but unlike a molecule carrying nonzero electric charge.
Polyatomic ion per se is not a compound, but it can be part of an ionic compound when
combined with an ion of opposite charge. The electric charge must be indicted when a formula
of it is written unless the ion is combined with another ion in the formula of an ionic compound.
Examples: NH4+; Hg22+; NO3–; SO32–. (SO3 is not the same as SO32–.)
ACID
A covalent compound whose molecules have a special hydrogen atom that can be detached
from the rest of the molecule as hydrogen ion (H+) in an aqueous solution. The rest of the
molecule becomes a negatively charged ion. A pure acid may not conduct electricity, but its
aqueous solution (acid mixed with water) does conduct electricity. The sour taste of acids is due
to hydrogen ion.
Matter
(solid, liquid, gas)
Physical Change
Substances
(constant composition)
Chemical Change
Elementary Substances
Metals
Atom
Nonmetals
Atom
Compounds
Organic
Compounds
Inorganic
Compounds
Metalloids
Molecule
O2, O3, Cl2,
P4, S8
Atom
Ionic
Compounds
Covalent
Compounds
Formula Unit
Molecule
Formula Unit
SiO2(quartz), SiC
Mixtures
(variable composition)
Homogeneous
Mixtures (or Solutions)
Representative
Particle
Heterogeneous
Mixtures
SUMMARY OF NOMENCLATURE SYSTEM
SUBSTANCE
OR ION
NAME
FORMULA
Elementary
Substance
Name of element
Symbol of element; common exceptions:
H2, N2, O2, F2, Cl2, Br2, I2
Monatomic Cation
Name of element followed by ion; if element
forms more than one monatomic cation,
elemental name is followed by ion charge in
Roman numerals and in parentheses
Symbol of element followed by superscript
to indicate charge
Monatomic Anion
Name of element changed to end in –ide
followed by ion
Symbol of element followed by superscript
to indicate charge
Compounds made
up of atoms of two
nonmetals
First element in formula followed by second,
change to end in -ide; each element
preceded by prefix to show the number of
atoms in the molecule
Symbol of first element in name followed
by symbol of second element, with
subscript to show number of atoms in the
molecule
Acid
Most common: middle element changed to
end in -ic
One more oxygen than -ic acid: add prefix
per- to name of -ic acid
One fewer oxygen than -ic acid: change
ending of -ic acid to -ous
Two fewer oxygens than -ic acid: add prefix
hypo- to name of -ous acid
No oxygen: Prefix hydro- followed by name of
second element changed to end in –ic
H followed by symbol of nonmetal followed
by O (if necessary), each with appropriate
subscript
MEMORIZE THE FOLLOWING:
Nitric acid: HNO3
Sulfuric acid: H2SO4
Carbonic acid: H2CO3
Phosphoric acid: H3PO4
Chloric acid: HClO3
Acetic acid: HC2H3O2
Polyatomic anion
from total
ionization of
oxyacid
Replace -ic in acid name with -ate, or replace
-ous in acid name with -ite, followed by ion
Acid formula without hydrogen plus
superscript showing negative charge equal
to number of hydrogens removed from
acid formula
Polyatomic anion
from step-by-step
ionization of
oxyacid
Hydrogen followed by name of ion from total
ionization of acid (dihydrogen in the case of
H2PO4–)
Acid formula minus one (or two for H3PO4)
hydrogen(s), plus superscript showing
negative charge equal to number of
hydrogen atoms removed from acid
formula
Other polyatomic
ions
Ammonium ion
Hydroxide ion
Mercury (I) ion
NH4+
OH–
Hg22+
Ionic Compound
Name of cation followed by name of anion
(omitting ion in each of the names)
Formula of cation followed by formula of
anion (usually no charges indicated), each
taken as many times as necessary to yield
a net charge of zero (polyatomic ion
formulas enclosed in parentheses if taken
more than once)
Hydrated Salt
Name of anhydrous compound followed by
(number prefix)hydrate, where (number
prefix) indicates the number of water
molecules associated with one formula unit of
anhydrous compound
Formula of anhydrous compound followed
by “∙X H2O” where X is the number of
water molecules associated with one
formula unit of anhydrous compound
Naming Inorganic Compounds
yes
(= ionic compound)
yes
Group I or II;
Al, Ag, Zn, NH4?
no
Metal
or NH4?
(= covalent compound)
no
yes
yes
O is present,
but not H2O or
H2O2?
yes
Type I Ionic
Compound
Type II Ionic
Compound
Al2O3 (s)
aluminum oxide
LiOH (s)
lithium hydroxide
AgNO3(s)
silver nitrate
Na2O2(s)
sodium peroxide
CaCO3(s)
calcium carbonate
NH4NO3(s)
ammonium nitrate
CuCl(s)
copper(I) chloride
CuCl2(s)
copper(II) chloride
Fe2O3(s)
iron(III) oxide
FeO(s)
iron(II) oxide
Cr2(SO4) 3(s)
chromium(III) sulfate
MnS(s)
manganese(II) sulfide
Sn(NO3) 2(s)
tin(II) nitrate
Oxyacid
HClO(aq)
hypochlorous acid
HClO2(aq)
chlorous acid
HClO3(aq)
chloric acid
HClO4(aq) or (l)
perchloric acid
H2SO3(aq)
sulfurous acid
H2SO4(aq) or (l)
sulfuric acid
Nonoxyacid
HCl(aq)
hydrochloric acid
H2S(aq)
hydrosulfuric acid
HCN(aq)
hydrocyanic acid
H in front?
no
no
(aq) is written?
no
Binary Covalent Compound
HCl(g)
hydrogen chloride
H2S(g)
hydrogen sulfide
HCN(g)
hydrogen cyanide
H2O2(l)
hydrogen peroxide
H2O(l)
water
P2O5(s)
diphosphorus pentoxide
NO2(g)
nitrogen dioxide
S2Cl2(l)
disulfur dichloride
CO(g)
carbon monoxide
PF5(g)
phosphorus pentafluoride
XeF4(s)
xenon tetrafluoride
NH3(g)
ammonia
CH4(g)
methane
CHEMICAL SYMBOLS AND FORMULAS
Al
1) Element aluminum
Example: Al is the third most abundant element in the Earth crust.
2) Elementary substance (aluminum metal)
Example: 5.0 grams of Al.
3) One atom of aluminum
2Al
Two (individual) atoms of aluminum
2H
Two (individual) atoms of hydrogen
H2
1) Molecular hydrogen; substance (hydrogen gas)
Example: A balloon is filled with H2 gas.
2) One molecule of hydrogen
H2 O
1) Water as a substance (a covalent compound)
Example: 50 mL of H2O.
2) One molecule of water
2H2O
Two molecules of water
2Al + 3O2
Two atoms of aluminum mixed with three molecules of oxygen
Al2(SO4)3
1) Aluminum sulfate as a substance (an ionic compound)
Example: 3.30 grams of Al2(SO4)3.
2) One formula unit of aluminum sulfate:
each 2 atoms of aluminum chemically combined with 3 SO4 groups
(atoms of aluminum, sulfur and oxygen chemically combined in the
ratio of 2:3:12)
GREEK PREFIXES FOR NAMING COMPOUNDS
Number
Prefix
1/2
hemi-
1
mono-
2
di-
bicycle
3
tri-
tricycle
4
tetra-
5
penta-
6
hexa-
7
hepta-
September
8
octa-
October
9
nona-
10
deca-
11
undeca-
12
dodeca-
13
trideca-
20
icosa-
the Pentagon
(Latin)
November
December
(Latin)
Prefixes that are in bold should be memorized!!!
NAMES AND FORMULAS OF COMMON IONS
POSITIVELY CHARGED IONS (CATIONS)
NEGATIVELY CHARGED IONS (ANIONS)
The charges of these ions can be figured out
using the periodic table:
The charges of these ions can be figured out
using the periodic table:
H+
Li+
Na+
K+
Rb+
Cs+
Be2+
Mg2+
Ca2+
Sr2+
Ba2+
Al3+
hydrogen ion
lithium ion
sodium ion
potassium ion
rubidium ion
cesium ion
beryllium ion
magnesium ion
calcium ion ion
strontium ion
barium ion
aluminum ion
These ions must be memorized:
hydronium ion
ammonium ion
silver ion
cadmium ion
zinc ion
copper (I) or cuprous ion
copper (II) or cupric ion
mercury (I) or mercurous ion
mercury (II) or mercuric
lead (II) or plumbous ion
lead (IV) or plumbic ion
iron (II) or ferrous ion
iron (III) or ferric ion
manganese (II) ion
nickel (II) ion
tin (II) or stannous ion
tin (IV) or stannic ion
chromium (II) ion
chromium (III) ion
cobalt (II) ion
cobalt (III) ion
bismuth (III) ion
hydride ion
fluoride ion
chloride ion
bromide ion
iodide ion
oxide ion
sulfide ion
nitride ion
phosphide ion
H–
F–
Cl–
Br–
I–
O2–
S2–
N3–
P3–
These ions must be memorized:
H3 O+
NH+4
Ag+
Cd2+
Zn2+
Cu+
Cu2+
Hg2+
2
Hg2+
Pb2+
Pb4+
Fe2+
Fe3+
Mn2+
Ni2+
Sn2+
Sn4+
Cr2+
Cr3+
Co2+
Co3+
Bi3+
acetate ion
hydroxide ion
cyanide ion
cyanate ion
thiocyanate ion
perchlorate ion
chlorate ion
chlorite ion
hypochlorite ion
nitrate ion
nitrite ion
permanganate ion
carbonate ion
hydrogen carbonate or bicarbnate ion
chromate ion
dichromate ion
peroxide ion
sulfate ion
hydrogen sulfate or bisulfate ion
sulfite ion
hydrogen sulfite or bisulfite ion
phosphate ion
hydrogen phosphate ion
dihydrogen phosphate ion
borate ion
oxalate ion
Note: Ions in bold type are very common and must be memorized first!!!
C2 H3 O–2
OH–
CN–
OCN–
SCN–
ClO–4
ClO–3
ClO–2
ClO–
NO–3
NO–2
MnO–4
CO2–
3
HCO–3
CrO2–
4
Cr2 O2–
7
O2–
2
SO2–
4
HSO–4
SO2–
𝟑
HSO–3
PO3─
4
HPO2–
4
H2 PO–4
BO3–
3
C2 O2–
4
MONATOMIC IONS
IA
VII A
H+
H−
II A
IV A
VA
VI A
Be2+
C4−
N3−
O2−
F−
Na+ Mg2+
Al3+ Si4−
P3−
S2−
Cl−
Li+
K
+
Ca
+
Rb
+
Cs
2+
2+
Sr
Ba
2+
III A
III B
IV B
VB
VI B
Cr2+
Cr3+
VII B
2+
Mn
VIII B
VIII B
Fe2+
Fe3+
Co2+
Co3+
VIII B
Ni
2+
IB
II B
Cu+
Cu2+
Zn2+
+
2+
Ag
Cd
Au+ Hg 22+
Au3+ Hg2+
As3− Se2− Br−
Sn2+
Te2− I−
4+
Sn
Pb2+
Pb4+
Bi3+
En+ metallic elements that form a single stable monatomic cation:
Ba2+ is barium ion, Al3+ is aluminum ion, etc.
En+
metallic elements that form several stable monatomic cations:
Cr3+ is chromium (III) ion, Hg2+ is mercury (II) ion, etc.; Hg 22+ is a polyatomic ion called mercury (I) ion
En− nonmetallic elements; each forms a single stable monatomic anion:
F− is fluoride ion, Si4− is silicide ion, etc.
ions that do not exist in aqueous solutions; they react with water by accepting either H+
or OH− ions (small amounts of H+ and OH− ions are always present in water: H2O ⇆ H+ + OH−)
VIII A
OXYACIDS AND OXYANIONS
SO32─
sulfite ion
minus H+
HSO3─
NO2─
hydrogen
sulfite ion
nitrite ion
minus H+
minus H+
H2SO3
HNO2
sulfurous acid
nitrous acid
minus O
HNO3
nitric acid
minus H+
NO3
─
nitrate ion
minus O
H2CO3
carbonic acid
minus H+
HCO3─
hydrogen
carbonate ion
minus H+
CO32─
carbonate ion
H2SO4
sulfuric acid
minus H+
HSO4─
hydrogen
sulfate ion
minus H+
SO42─
sulfate ion
H3PO4
phosphoric acid
minus H+
H2PO4─
dihydrogen
phosphate ion
minus H+
HPO42─
hydrogen
phosphate ion
minus H+
PO43─
phosphate ion
OXYACIDS *
OXYANIONS
H2O (HOH) water
OH −
HC2H3O2 (aq) acetic acid
C2H3O 2− acetate ion
HClO4 (aq)
perchloric acid
ClO 4−
perchlorate ion
HClO3 (aq)
chloric acid
ClO 3−
chlorate ion
HClO2 (aq)
chlorous acid
ClO 2−
chlorite ion
HClO (aq)
hypochlorous acid
ClO −
hypochlorite ion
HNO3 (aq)
nitric acid
NO 3−
nitrate ion
HNO2 (aq)
nitrous acid
NO 2−
nitrite ion
H2CO3 (aq)
carbonic acid
CO 23−
carbonate ion
hydroxide ion
HCO 3− hydrogen carbonate ion
(bicarbonate ion)
H2SO4 (aq)
sulfuric acid
SO 24−
sulfate ion
HSO −4 hydrogen sulfate (bisulfate ion)
H2SO3 (aq)
sulfurous acid
SO 32 −
sulfite ion
HSO 3− hydrogen sulfite ion (bisulfite ion)
H3PO4 (aq)
phosphoric acid
PO 34 −
phosphate ion
HPO 24 − hydrogen phosphate ion
H2PO −4 dihydrogen phosphate ion
*
Pure covalent molecular compounds or their aqueous solutions. Usually, only acids
with the highest number of oxygen atoms (HClO4, HNO3, H3PO4, H2SO4) can be
obtained in pure form. Those are also stable in aqueous solutions. All other acids exist
only as aqueous solutions. Organic acids, such as acetic acid, are stable in pure form
and in aqueous solutions.
NONOXYACIDS AND NONOXYANIONS
COMPOUNDS
ACIDS
ANIONS
pure substances:
only HX molecules
aqueous solutions:
HX dissolved in H2O
exist in ionic crystals
or as X−(aq) in aqueous
solutions
HF(g)
hydrogen fluoride
HF(aq)
hydrofluoric acid
F−
fluoride ion
HCl(g) hydrogen chloride
HCl(aq) hydrochloric acid
Cl− chloride ion
HBr(g) hydrogen bromide
HBr(aq) hydrobromic acid
Br− bromide ion
HI(g)
HI(aq)
I−
hydrogen iodide
hydroiodic acid
iodide ion
H2S(g) hydrogen sulfide
H2S(aq) hydrosulfuric acid
S2− sulfide ion
HS− hydrogen sulfide ion
HCN(g) hydrogen cyanide
HCN(aq) hydrocyanic acid
CN− cyanide ion
PREFIXES AND SUFFIXES IN THE NAMES OF ACIDS
AND THE CORRESPONDING ANIONS
Number of
Oxygen Atoms
Acid
Anion
Greatest
per– ...... –ic acid
Greater
....... –ic acid
....... –ate ion
Smaller
....... –ous acid
....... –ite ion
Smallest
None
hypo– ..... –ous acid
per– ...... –ate ion
hypo– ..... –ite ion
hydro– ....... –ic acid
....... –ide ion
EXAMPLE:
HClO4(aq)
perchloric acid
ClO−
perchlorate ion
4
HClO3(aq)
chloric acid
HClO2(aq)
chlorous acid
ClO−
3 chlorate ion
HClO(aq)
hypochlorous acid
HCl(aq)
hydrochloric acid
ClO−
2 chlorite ion
ClO−
hypochlorite ion
Cl−
chloride ion