ACTIVITY 1
Naming and Writing Formulas for Binary Chemical
Compounds
WHY?
Without an accepted system for naming and writing formulas for compounds chaos would
result. You will learn the accepted system for naming simple binary chemical compounds.
LEARNING OUTCOMES
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Identify if a compound is covalent or ionic.
Name a simple binary compounds given its formula.
Write the formula for a simple binary compound given its name.
INFORMATION
Previously you discovered the charge that will result on certain atoms when they react to
form an ion. Positively charged ions (called cations) and negatively charged ions (called anions)
are attracted to each other and can come together to form an ionic bond and the resulting
compound is called an ionic compound. Oppositely charged ions come together in such a way to
be electrically neutral, meaning that the sum of the positively charged ions and negatively
charged ions must be zero.
Review Questions, 1 through 3, to be done before class.
1. What is always the charge (positive or negative) of a metal when it reacts with a
nonmetal? What is always the charge of a nonmetal when it reacts with a metal?
2. Write the charge of ion in the table that will result for the following atoms when they
react. Additionally, indicate if the ion is a cation or anion.
Atoms
Charge of the ion upon
Cation or Anion
reacting
Column 1A (Li, Na, K, Rb, Cs)
Column 2A (Be, Mg, Ca, Sr,
Ba)
Column 6A (O, S, Se, Te)
Column 7A (F, Cl, Br, I)
3. Based on the trends observed in the table what do you think will be the charge on the
nonmetals in group 5A (N and P) when they form ions? What will be the charge (value
and sign) of the ion form from aluminum? Note: Aluminum is a metal.
Model 1: The reaction of magnesium (a metal) and chlorine (a nonmetal) to form magnesium
chloride. The formula is given below.
MgCl2
Key Questions:
1. The compound, MgCl2, is an ionic compound. How do you know?
2. Magnesium underwent a reaction to form an ion in this compound. What is its charge?
3. Likewise, chlorine underwent a reaction to form an ion in this compound. What is the
charge on each ion?
4. What is the ratio of cations to anions in magnesium chloride?
5. Using the fact that the ions must come together in a way to be electrically neutral, explain
the ratio of cations to anions in this compound.
Note: The subscripts in a chemical formula for an ionic compound are always written in the
smallest whole-number ratio.
Exercises:
1. Write the chemical formula for the following.
a. An ionic compound formed from Li and I.
b. An ionic compound formed from Na and O.
c. An ionic compound formed from Al and O.
d. An ionic compound formed from Fe2+ and Cl.
Ions can also come in the form of polyatomic ions. This is a group of atoms bound together that
contain a specified charge. An example would be hydroxide which has a formula of OH-. The
oxygen and hydrogen bound together would contain a -1 charge. If more than one polyatomic
ion is needed to obtain electrical neutrality, parentheses are use for the polyatomic ion. The
formula for magnesium hydroxide would be Mg(OH)2. A table of polyatomic ions is included at
the end of this activity.
2. Write the chemical formula for ionic compound formed from Ca and the polyatomic ion
C2H3O2-.
Model 2: Naming an Ionic Compound
Name of compound
NaCl
CaF2
Na3N
Sodium chloride
Calcium fluoride
Sodium nitride
Key Questions:
1. What is the name of the cation in each ionic compound?
2. How does the name of the cation compare to the name of the element on the periodic
table before it forms a cation?
3. What are the names of the anions?
4. How does the name of anion compared to the name of the element on the periodic table
before it forms an anion?
5. Are the subscripts in the formula included in the naming of the ionic compound?
The changes reflected in questions #2 and #4 always hold when naming ionic compounds with
one type of atom for the cation and one type of atom for the anion. There are minor changes in
naming depending on the type of cation and/or anion. These are listed below.
Many metals can form ions of differing positive charges. For example, Fe atoms can form Fe2+
or Fe3+ cations. This is especially prevalent for transition metals (see periodic table from
previous activity). A table listing some of these metals is shown at the end of this activity.
When writing a formula for an ionic compound that contains such a metal, a roman numeral must
be placed after the name of the cation specifying the charge. For example, FeO would be iron(II)
oxide.
6. Write the name for CuF2 and Cr2S3.
There are ionic compounds that contain polyatomic ions. The same rules are used as specified
previously. The only difference is that you must name the polyatomic ion as given in the table
shown at the end of activity. For example, Na2SO4 would be sodium sulfate. You need to
memorize the polyatomic ions given in this table.
7. Name of the following compounds.
a. Ca(NO2)2
b. (NH4)2S
Be sure to practice doing some naming of and formula writing for ionic compounds.
Table 2.5.1[Table 2.2]
Important and Common Polyatomic Ions
The names of many polyatomic ions end in “-ate”.
Nitrate
Sulfate
NO3⁻
CO32⁻ Carbonate
SO42−
PO43− Phosphate
Chlorate
Chromate
ClO3⁻
SiO32⁻ Silicate
CrO42−
2−
2−
Bromate
Thiosulfate
Oxalate
BrO3⁻
S2O3
C2O4
Iodate
IO3⁻
If they have one less oxygen than the “-ate” ion, use the suffix “-ite” instead.
Nitrite
Sulfite
NO2⁻
SO32−
Chlorite
ClO2⁻
Bromite
BrO2⁻
Iodite
IO2⁻
If they have one less oxygen than the “-ite” ion, add the prefix “hypo-”.
Hypochlorite
ClO⁻
Hypobromite
BrO⁻
Hypoiodite
IO⁻
If they have one more oxygen than the “-ate” ion, add the prefix “per-“.
Perchlorate
ClO4⁻
Perbromate
BrO4⁻
Periodate
IO4⁻
If H is present, add the prefix “bi-“ or “hydrogen-“ and add +1 to the charge (but if that
makes it electrically neutral it is no longer a polyatomic ion). If “hydrogen-“ is used, emphasize
that it is an ion.
Bicarbonate or the hydrogen carbonate ion
HCO3−
−
Bisulfide or the hydrogen sulfide ion
HS
Bisulfate or the hydrogen sulfate ion
HSO4−
Bisulfite or the hydrogen sulfite ion
HSO3−
The hydrogen phosphate ion or the monohydrogen phosphate ion (“bi-“ is not used
HPO42−
here)
The dihydrogen phosphate ion (“bi-“ is not used here)
H2PO4−
Miscellaneous ions
NH4⁺
Ammonium
OH−
Hydroxide MnO4−
Permanganate
+
−
H 3O
Hydronium
CN
Cyanide
Cr2O72− Dichromate
Hg22+
Mercury(I)
O22−
Peroxide
OCN−
Cyanate
SCN−
Thiocyanate
C2H3O2− Acetate (also CH3COO− or
CH3CO2−)
Part 2
Model 1: The reaction of nitrogen (a nonmetal) and oxygen (a nonmetal) to form nitrogen
dioxide. The formula is given below.
NO2
Key Questions:
1. The compound, NO2, is a covalent compound. How do you know?
2. What is the ratio of nitrogen to oxygen in this compound? Does the name it is given,
nitrogen dioxide, have any connection to this ratio?
Exercises:
1. Write the chemical formula for the following using table 2.3 found at the end of this
section.
a. A covalent compound named nitrogen monoxide.
b. A covalent compound named sulfur hexafluoride.
c. A covalent compound named dichlorine heptaoxide.
d. A covalent compound named dinitrogen tetraoxide
It is not uncommon to encounter covalent compounds that the number of electrons being shared
varies. In time we will learn about how the number of shared electrons increases the number of
bonds found between different atoms. However, for now we will focus on learning to
understand the rules associated with naming these compounds.
Covalent compounds formed between carbon and hydrogen also have more commonly used
alternate names. This is a group of molecules are called hydrocarbons. You are responsible to
understand how to name the saturated hydrocarbon molecules of fitting the pattern CnH(2n+2) for
compounds with one carbon up to compounds with 10 carbons. List of these common saturated
hydrocarbons is included at the end of this section.
2. What would be the number of expected hydrogens for the compound propane which
contains 3 carbons? Can you determine this formula without using the table?
Model 2: Naming a Covalent Compound
Name of compound
H2O
Dihydrogen
CF4
C2H6
monoxide (water)
Carbon tetrafluoride
Dicarbon Hexahydride (ethane)
1. Write the name for P4O6 and SeBr4.
Table 2.3
Prefix
Meaning
Mono-*
1
Di-
2
Tri-
3
Tetra-
4
Penta-
5
Hexa-
6
Hepta-
7
Octa-
8
Nona-
9
Deca-
10
Common Saturated Hydrocarbons
CH4
C2H6
C3H8
C4H10
C5H12
C6H14
C7H16
C8H18
C9H20
C10H22
methane (“meth-“ indicates 1 C atom)
ethane (“eth-“ indicates 2 C atoms)
propane (“prop-“ indicates 3 C atoms)
butane (“but-“ indicates 4 C atoms)
pentane
hexane
heptane
octane
nonane
decane