BRITTON-DEERFIELD HIGH
SCHOOL
CHEMISTRY
CHAPTER 3: FORMULAS
AND NAMES OF
COMPOUNDS
GOALS
• To write a formula for a binary molecular compound
• To identify the anion and cation of an ionic compound
• To identify the charge and symbol of an ion
• To write the formula unit of an ionic compound
• To understand and recognize polyatomic ions
• To name a compound, given its formula or formula unit.
Molecular compounds
and formulas
LESSON 1 – MOLECULAR
COMPOUNDS AND
FORMULAS – OBJECTIVES
• Define a molecular compound
• Give the meaning of prefixes in molecular compound
names
• Write the formula for a binary molecular compound,
given its name
MOLECULAR
COMPOUND
• Molecular compound
• A compound containing atoms of two or more
elements that are bonded together by sharing
electrons
• Examples
• CO2
• H2 O
MOLECULE
• The chemical formula of a compound shows the atoms
in the smallest unit of that compound. This is called a
molecule.
• A neutral group of two or more atoms that are bonded
together by sharing electrons; the smallest unit of a
molecular compound.
PREFIXES
• Binary: molecular compounds consisting of two elements
• Silicon dioxide
silicon + oxygen
• Dihydrogen sulfide
hydrogen + sulfur
• Prefixes in names of molecular compounds do the same job as subscripts in
formulas
• Usually ends in –ide
• if the compounds ends in –ate or –ite, it usually contains 3 or more
elements.
Subscript
Prefix
Subscript
Prefix
1
mono-
6
hexa-
2
di-
7
hepta-
3
tri-
8
octa-
4
tetra-
9
nona-
5
penta-
10
deca-
PREFIXES (CONT.)
• Examples
• Sulfur hexafluoride
• Sulfur hexafluoride
• SF6
• Tetraphosphorus decoxide
• Tetraphosphorus decoxide
• P4O10
• Dinitrogen monoxide
• Dinitrogen monoxide
• N2O
Ions and Ionic
Compounds
LESSON 2 – IONS AND IONIC
COMPOUNDS – OBJECTIVES
• Explain how molecular and ionic compounds are
different
• Identify the cation and anion in a binary ionic
compound
• Write the symbol for an ion
• Explain what a roman numeral means in a compound
name.
MOLECULAR VS IONIC
COMPOUNDS
• Molecular compound
• A compound containing atoms of two or more
elements that are bonded together by sharing
electrons
MOLECULAR VS IONIC
COMPOUNDS
• Ionic compound
• A compound consisting of one kind of cation and
one kind of anion
• Ion
• An atom or group of atoms with a charge
• Cation
• An atom or group of atoms with a positive (+)
charge; a positive ion.
• Anion
• An atom or group of atoms with a negative (-)
charge; a negative ion.
IONS
• Taking away an electron from an atom gives a CATION
with a positive charge
• Adding an electron to an atom gives an ANION with a
negative charge.
• To tell the difference between an atom and an ion, look
to see if there is a charge in the superscript! Examples:
• Na
Ca
I
O
• Na+
Ca2+
I-
O2-
FORMING CATIONS &
ANIONS
A CATION forms
when an atom loses
one or more
electrons.
Mg --> Mg2+ + 2 e-
An ANION forms
when an atom gains
one or more
electrons
F + e- --> F-
PREDICTING ION
CHARGES
In general
• metals (Mg) lose electrons ---> cations
• nonmetals (F) gain electrons ---> anions
COMMON CATIONS
COMMON ANIONS
LEARNING CHECK
State the number of protons, neutrons, and
electrons in each of these ions.
39
K+
19
16O -2
41Ca +2
8
20
#p+ ______
______
_______
#no ______
______
_______
#e- ______
______
_______
LEARNING CHECK
Write the nuclear symbol form for the following atoms
or ions:
A. 8 p+, 8 n, 8 e-
___________
B.
17p+, 20n, 17e-
___________
C. 47p+, 60 n, 46 e-
___________
Ionic compounds
and formula units
LESSON 3 – IONIC
COMPOUNDS AND FORMULA
UNITS– OBJECTIVES
• Write the formula unit for a binary ionic compound,
given its name
• Determine if a formula unit is neutral
• Determine if a formula unit is in the simplest wholenumber ratio
IONIC FORMULAS
• Ionic compounds contain positively and negatively
charged ions.
• BUT, all ionic compounds are electrically neutral.
IONIC FORMULAS
• Your book uses calcium chloride for an example.
• The calcium (Ca2+) ion has a 2+ charge,
• located in column 2 on the periodic table
• The chlorine (Cl1-) ion has a 1- charge
• located in column 17 on the periodic table
So how does this work???
IONIC FORMULAS
CaCl
1Ca2+ + 1Cl1-
(2+) + (1-) = 1+
DOESN’T WORK
Ca2Cl
2Ca2+ + 1Cl1-
(2+) + (2+) + (1-) = 3+
DOESN’T WORK
CaCl2
1Ca2+ + 2Cl1-
(2+) + (1-) + (1-) = 0
We are now neutral, so this formula works!!!!
FORMULA UNIT
• Formula Unit
• A chemical formula for an ionic compound
• The simplest form of the compound
• Ionic compounds
• Formula units
• Molecular compounds
• formulas
FORMULA UNITS
What is the formula unit of the ionic compound, iron(II) fluoride?
Step 1: write the cation and anion in
symbols with ionic charges.
Fe2+
F-
Step 2: Make the number in the positive
charge into a subscript for the anion. Make
the number in the negative charge into a
subscript for the cation.
Fe
F2
Step 3: If necessary, reduce the resulting
formula to its smallest whole-number ratio.
To do this, divide all subscript by the larges
common factor.
FeF2
FORMULA UNITS
What is the formula unit of the ionic compound, titanium(III)
oxide?
Step 1: write the cation and anion in
symbols with ionic charges.
Ti3+
O2-
Step 2: Make the number in the positive
charge into a subscript for the anion. Make
the number in the negative charge into a
subscript for the cation.
Ti2
O3
Step 3: If necessary, reduce the resulting
formula to its smallest whole-number ratio.
To do this, divide all subscript by the larges
common factor.
Ti2O3
Polyatomic ions
and formula units
LESSON 4 – POLYATOMIC
IONS AND FORMULA UNITS–
OBJECTIVES
• Recognize common polyatomic ions
• Write a formula unit containing a polyatomic ion
QUICK REVIEW
• Molecule
• A neutral group of two or more atoms that are bonded
together by sharing electrons; the smallest unit of a
molecular compound.
• Molecular compound
• A compound containing atoms of two or more elements
that are bonded together by sharing electrons
• Ion
• An atom or group of atoms with a charge
• Ionic compound
• A compound consisting of one kind of cation and one
kind of anion
POLYATOMIC ION
• Polyatomic ion
• A group of two or more atoms that act as one ion and
has one charge
POLYATOMIC IONS
• A polyatomic ion is not the same as a
polyatomic molecule of an element.
• CHARGE !!!!
COMMON POLYATOMIC
IONS AND THEIR CHARGES
FORMULA UNITS FOR
POLYATOMIC IONS
• You will use the same rules you used for binary ionic
compounds.
• Only difference
• You add parenthesis around the symbol of a
polyatomic ion, putting the charge outside, like
so:
1• (NO3)
FORMULA UNITS FOR
POLYATOMIC IONS
What is the formula unit of the ionic compound, sodium
carbonate?
Step 1: write the cation and anion in
symbols with ionic charges.
Na1+
(CO3)2-
Step 2: Make the number in the positive
charge into a subscript for the anion. Make
the number in the negative charge into a
subscript for the cation.
Na2
(CO3)
Step 3: If necessary, reduce the resulting
formula to its smallest whole-number ratio.
To do this, divide all subscript by the larges
common factor.
Na2(CO3)
Parenthesis can be dropped
Na2CO3
FORMULA UNITS FOR
POLYATOMIC IONS
Lead(II) phosphate is an ionic compound. What is the formula
unit?
Step 1: write the cation and anion in
symbols with ionic charges.
Pb2+
(PO4)3-
Step 2: Make the number in the positive
charge into a subscript for the anion. Make
the number in the negative charge into a
subscript for the cation.
Pb3
(PO4)2
Step 3: If necessary, reduce the resulting
formula to its smallest whole-number ratio.
To do this, divide all subscript by the larges
common factor.
Pb3(PO4)2
Parenthesis cannot be dropped
Pb3PO42
FORMULA UNITS FOR
POLYATOMIC IONS
Iron(II) sulfate is an ionic compound. What is the formula unit?
Step 1: write the cation and anion in
symbols with ionic charges.
Fe2+
(SO4)2-
Step 2: Make the number in the positive
charge into a subscript for the anion. Make
the number in the negative charge into a
subscript for the cation.
Fe2
(SO4)2
Step 3: If necessary, reduce the resulting
formula to its smallest whole-number ratio.
To do this, divide all subscript by the larges
common factor.
Fe2(SO4)2
Are we done???
Smallest Unit
FeSO4
Names of
Compounds
LESSON 5 – NAMES OF
COMPOUNDS – OBJECTIVES
• Name a molecular compound, given its formula
• Name an ionic compound given its formula unit
• Recognize common acids by their formula
RULES FOR USING
PREFIXES
Rule 1: Prefixes are only for BINARY COVALENT compounds.
Rule 2: The prefix mono- is never used on the first element
of a binary covalent compound. Without a prefix it is
assumed that there is only 1.
Example: CO2 is carbon dioxide, and
not monocarbon dioxide.
Rule 3: Remove the -o or -a from a prefix before adding it
to oxide.
Example: CO is carbon monoxide, and
not carbon monooxide.
STEPS FOR NAMING
BINARY COVALENT COMPOUNDS
N 2 O4
dinitrogen
tetroxide
Step 1: Write the name of the first nonmetal.
Step 2: Write the name of the second nonmetal
changing its ending to -ide.
Step 3: Add prefixes to specify how many of each
element are present.
IMPORTANT FACT
Because hydrogen only has 1 proton and 1 electron, it
behaves differently than any other element on the
periodic table of elements.
H+
H-
Hydrogen
can donate
its 1 electron.
Hydrogen
can gain 1
electron.
H2
Hydrogen
can share
electrons.
This means that hydrogen can act as either a metal
or a nonmetal!
NAMING
IONIC COMPOUNDS
When metals lose electrons they become ions, but
their name does not change.
Na
Na+
sodium
sodium
Mg
magnesium
Mg2+
+
eelectron
+
magnesium
2e2 electrons
RULES FOR NAMING IONS
When nonmetals gain electrons they become ions,
and their name does change.
F
+
fluorine
S
sulfur
+
e-
F-
electron
fluoride
2e-
S2-
2 electrons
sulfide
RULES FOR NAMING IONS
1. The names of metals do not change.
2. Changing the name of nonmetals:
root of element name + -ide =
name of ion
Examples:
The name of chlorine’s ion:
chlor- + -ide = chloride
The name of nitrogen’s ion:
nitr- + -ide = nitride
EXAMPLES OF NAMING
IONS:
The name of calcium’s ion:
calcium
(The names of metals don’t change!)
The name of oxygen’s ion:
ox- + -ide = oxide
The name of aluminum’s ion:
aluminum
(The names of metals don’t change!)
STEPS FOR NAMING IONIC
COMPOUNDS
• Step 1: Write the name of the cation. In a formula unit, the
cation is given first. If the cation is an element, write its name.
If the cation is a polyatomic ion, write its name.
• Step 2: Write the name of the anion. If the anion is an
element, change the ending to -ide. If the anion is a
polyatomic ion, do not change its name. There are no
prefixes to add to ionic compound names.
• Step 3: Many metals in the center of the periodic table
have more than one possible charge. These metals include
iron, chromium, manganese, nickel, copper, tin, lead, and
gold. If the cation in a formula unit is one of these, the
correct charge needs to be shown in the name. The correct
charge is the one that makes the compound neutral. It is
shown by adding a Roman numeral in parentheses after the
cation’s name.
Be very careful that you do not mix up the names of
ions. This is very common for beginners to naming.
Decide which name goes with each ion.
N-3
nitrate
NO3-
nitride
S-2
sulfide
SO3-2
sulfite
P-3
phosphate
phosphide
PO4-3
HELPFUL HINT:
If the ion ends in –ide, it is probably from the
periodic table. If the ion ends in –ate or –ite, it is a
polyatomic ion.
Examples:
sulfate
sulfide
sulfite
-2
SO4
-2
S
-2
SO3
nitride
nitrite
nitrate
-3
N
NO2
NO3
ACIDS
• Acid
• A compound that produces H1+ ions when dissolved in
water.
Table 3.5.2 Common Acids
Formula
Name
HCl
Hydrochloric acid
HBr
Hydrobromic acid
HNO3
Nitric acid
NClO3
Chloric acid
HClO4
Perchloric acid
H2SO4
Sulfuric acid
H3PO4
Phosphoric acid
HC2H3O2
Acetic acid