Chapter 3 – Compounds
Chemical Symbol – this is a shorthand representation of the name of
an element.
ie. C – carbon
Ag – silver
 We use symbols when we are writing chemical formulas.
Chemical Formula – this is a combination of symbols and subscripts
that represent the composition of a compound.
ie. H2O = 2 hydrogen atoms and 1 oxygen atom
subscript
 If there is no subscript it is assumed that there is only 1 atom
or ion.
Writing Chemical Formulas (only need to do for ionic compounds)
monatomic ion – is a single charged atom. (metals are +ve and
nonmetals are – ve )
ie. sodium ion - Na +
bromide ion - Br –
polyatomic ion – is a group of covalently bonded atoms with an overall
charge.
ie. nitrate ion – NO3 –
phosphate ion – PO4 3-
oxidation number – this represents the apparent charge on the atoms.
 We use oxidation #’s to write chemical formulas.
ie. N 3-
oxidation number
Procedure :
1) Write down the ions with the proper charge.
2) Do a cross replacement. ie. K+1O2- = K2O
3) Reduce subscripts to the lowest terms.
 Total charges must add up to zero.
ie. Mg 2+ N 3Pb 4+ O 2-
Mg3N2
Pb2O4
PbO2
 If there is more than 1 polyatomic ion in a compound we put it
inside of brackets.
ie. Ba 2+ NO 3-
Ba (NO3)2
this tells us there are 2 nitrate ions.
Sn 4+ CO3 2-
Sn2(CO3)4
Sn (CO3)2
(reduce)
Naming Compounds
1. Binary Ionic Compounds (only 1 oxidation #)
 Made of a metal and a nonmetal.
Procedure :
i)
ii)
Write the name of the positively charged element. (metal)
Add the name of the negatively charged element but change its
ending to “ide”.
ie. NaCl – sodium chloride
K2S – potassium sulfide
2. Binary Ionic Compounds (metal with more than 1 oxidation #)
Procedure : same as for #1, except you must indicate the oxidation
number of the metal using a Roman Numeral. The Roman Numeral is
put in brackets after the metals name.
 Common metals with more than 1 oxidation state.
Pb, Sn, Fe, Co, Cu, Hg, Mn, Au, Ni
ie. PbS – lead (II) sulfide
CrCl3 – chromium (III) chloride
3. Binary Molecular Compounds
 Made of 2 nonmetals.
Procedure : Same as # 1 except you must use a prefix to tell how many
of each atom there are.
1 – mono
6 – hexa
2 – di
7 – hepta
3 – tri
8 – octa
4 – tetra
9 – nona
5 – penta
10 – deca
ie. CCl4 – carbon tetrachloride SF2 – sulfur difluoride
4. Compounds with Polyatomic Ions
Procedure :
i)
Name of the metal stays the same and the polyatomic ion is
named according to the rules below.
ii) If the positive ion has more than 1 oxidation #, Roman
Numerals must be used.
prefix root
suffix
ion
1 more oxygen
most common
1 less oxygen
2 fewer oxygens
per
ate
ate
ite
ite
hypo
NO4NO3NO2NO-
pernitrate
nitrate
nitrite
hyponitrite
ie. FeCO3 – iron (II) carbonate
FeCO2 – iron (II) carbonite
Fe2(CO3)3 – iron (III)carbonate
Fe2(CO2)3 – iron (III)carbonite
5. Ionic Hydrates
 These are ionic compounds with water molecules chemically bonded
to the compound.
 They decompose at relatively low temperatures, producing water and
an anhydrous compound.
anhydrous – means no water.
 Hydrates are written in the general form:
Y . X H2O
Y = ionic compound
X = # of water molecules
Procedure :
i)
name the ionic compound as usual.
ii) use a prefix to represent the number of water molecules
followed by hydrate.
ie. CuSO4 . 5 H2O
copper sulfate pentahydrate
.
Na2CO3 10 H2O sodium carbonate decahydrate
Terminology
1.Molecule – a particle made up of 2 or more covalently bonded
nonmetallic atoms.
ie. H2O, CO2, CCl4
2.Diatomic Molecule – a molecule made up of 2 atoms of the
same element. There are 7 of them.
H2, N2, O2, F2, Cl2, Br2, I2
3.Polyatomic Molecule – a molecule made up of more than 2
atoms of the same element. There are 3 of them.
O3, P4, S8
4. Molecular Formula – a formula indicating the actual number
of each kind of atom contained in a molecule.
ie. C6H12 – molecular formula for hexane.
5. Empirical Formula – a formula giving the lowest whole
number ratio of the atoms present in a compound.
ie. CH2 – empirical formula for hexane.
6. Formula Unit – a term usually used to describe or show the
lowest whole number ratio of the ions in an ionic compound.
7. Coefficient – a number used to indicate the number of
molecules or formula units.
 It is placed in front of the compound and is mostly used when
balancing equations.