Lab 5
Name_____________________________
How Are Ionic and Covalent Compounds Named
and Represented Symbolically?
Pre-Lab Assignment
There is no written pre-lab assignment for this laboratory exercise.
Recommended: Review the element names, symbols, and ions they form as well as the polyatomic ions.
Learning Goals
Write the proper name of the ionic or binary covalent compound from the formula.
Write the proper formula for the ionic or binary covalent compound from the name.
ChemActivity
From “Explorations in Conceptual Chemistry,” by Jeffrey Paradis.
Answer the following critical thinking questions to help you understand the rules for naming ionic compounds.
Part 1
Information: NaCl is called sodium chloride.
1.
Ionic compounds contain a metal and a nonmetal. Which is the metal? Which is the nonmetal?
2.
Where is the metal written in the formula?
3.
Where is the nonmetal written in the formula?
4.
What happened to the name of the metal when it went from being a pure element to being part of an ionic compound?
5.
What happened to the name of the nonmetal when it went from being a pure element to being part of an ionic compound?
6.
Part 1 Summary: What you have learned from Part 1 about naming ionic compounds?
Part 2
Information: MgI2 is called magnesium iodide.
7.
Does the name of this compound follow the rules determined in questions 1-5?
8.
What is the charge on the magnesium ion?
9.
What does the charge on the magnesium ion have to do with the number of valence electrons that an atom of magnesium has?
10. How many iodide ions are needed to cancel out the charge of a magnesium ion making a neutral compound?
11. How is the number of iodide ions needed in question 9 indicated in the formula?
12. Part 2 Summary: How are subscripts in formulas for ionic compounds determined? Are they specifically reflected in the name
of the compound? Why or why not?
Lab 5: How Are Ionic and Covalent Compounds Named and Represented Symbolically?
Part 3
2
Information: CuCl is called copper (I) chloride. CuCl2 is called copper (II) chloride. FeO is called iron (II) oxide.
Fe2O3 is called iron (III) oxide.
13. What is the charge on the chloride ion?
14. Knowing the charge on the chloride ion, what must be the charge on the copper ion in the first compound?
15. How is the charge on the copper ion indicated in the name of the first compound?
16. Knowing the charge on the chloride ion, what must be the charge on the copper in the second compound?
17. How is the charge on the copper ion indicated in the name of the second compound?
18. Why don’t we need to use Roman numerals with Group IA and Group IIA elements (and aluminum)?
19. Part 3 Summary: Based on the information from Part 3, what do you think is the general rule for naming main group metals
versus transition metals in ionic compounds?
Part 4
Information: Na2CO3 is called sodium carbonate. Mg(NO3)2 is called magnesium nitrate. Pb(NO2)2 is called lead
(II) nitrite. CaCO3 is called calcium carbonate. NaNO3 is called sodium nitrate.
20. What do we do to the name of a polyatomic ion when we include it in an ionic compound? Refer to Appendix I on p. 6.
21. When do we use parentheses in writing the formula for an ionic compound? Your answer should explain why Mg(NO3)2 has
parentheses, but NaNO3 does not.
22. Will the formula for a compound such as calcium chloride need parentheses? Why or why not?
Background
An ionic compound can be recognized by the presence of a metal and a nonmetal in the formula or name.
A covalent compound can be recognized by the presence of two or more nonmetals present in the formula or name.
In an ionic compound, metals form positive ions (cations) and non-metals form negative ions (anions).
Chemical formulas of ionic compounds result from combining cations with anions in ratios that result in a net charge of zero for
the compound. All compounds are neutral – no overall charge.
Cations and anions take different forms:
•
Type I metal cations always take the same positive charge. Examples: Na+, Mg2+, Al3+
•
Type II metal cations can vary in charge, but are always positive. Examples: Fe2+/Fe3+, Cu+/Cu2+
•
Most representative (main group) elements are Type I and most transition elements are Type II. Exceptions to memorize: Zn2+,
Ag+, Cd2+ are Type I. Sn2+/Sn4+, Pb2+/Pb4+ are Type II.
•
Polyatomic cations contain groups of atoms acting as a single positive ion. The most common is NH4+, ammonium ion.
•
Representative nonmetal anions always take the same negative charge. (e.g. chloride ion is always Cl-, oxide ion is always O2-)
•
Polyatomic anions contain groups of atoms acting as a single negative ion. There are many - see a partial list of polyatomic
ions in Appendix I.
Lab 5: How Are Ionic and Covalent Compounds Named and Represented Symbolically?
3
Writing the name from the formula
Flowchart
Refer the following flow chart when studying and applying the steps for writing a compound name from its formula. The specific
steps are given on the next page.
Steps
1.
Is the compound ionic or covalent?
Ionic compounds contain a cation and an anion. Covalent compounds share electrons in bonds.
A. Two or more nonmetals bonded (no metals) is a covalent compound.
• Exception: polyatomic cation bonded with any anion (e.g. NH4Cl, ammonium chloride, is ionic).
• We will consider only binary covalent compounds here for simplicity (two nonmetals bonded).
Note: Acids are a special type of covalent compound that have their own nomenclature rules. Acids will be covered next
term.
B. A metal and a nonmetal bonded (cation+anion) is an ionic compound.
• One metal + one nonmetal is a binary ionic compound.
• One metal + more than one nonmetal is a polyatomic ionic compound.
Note: in this course we will not consider two or more metals bonded (no nonmetals).
2.
Use the appropriate rules (ionic or covalent) to name the compound.
A. Rules for binary covalent compounds (nonmetals bonded by sharing electrons)
• List the first element in the formula using a prefix for the number of atoms (except mono-).
• List the second element in the formula using a prefix for the number of atoms (except mono-) as well as the suffix “ide”. For a list of common prefixes, see Appendix II.
Examples: NO is nitrogen oxide; NO2 is nitrogen dioxide, N2O is dinitrogen oxide. (Note that carbon monoxide, CO, is an
exception to the rule.)
B. Rules for ionic compounds (cation+anion)
List cations first, then anions. Note: if there are more than two types of atoms in the formula, a polyatomic ion is present.
• Cations: name of the metal or polyatomic ion.
− Type I (only one possible charge on the cation): just the metal name
− Type II (more than one possible charge on the cation): metal name and Roman numeral corresponding to the
charge on the cation
− Polyatomic ion: memorize the name and formula in order to recognize it. (e.g. NH4+ is ammonium ion).
• Anions: in monatomic anion, change ending to –ide; if polyatomic ion, use memorized name.
− e.g. Cl is chlorine, but Cl- is chloride.
− Polyatomic ion: memorize the name and formula (e.g. NO3- is nitrate ion)
Examples: KCl is potassium chloride; KNO3 is potassium nitrate; NH4NO3 is ammonium nitrate.
Lab 5: How Are Ionic and Covalent Compounds Named and Represented Symbolically?
4
Writing the formula from the name
Steps
1.
2.
Is the compound ionic or covalent?
Use the appropriate rules (ionic or covalent) to determine the formula from the name.
A. For covalent compounds, write the symbols for each nonmetal in the compound name. Include subscripts describing the
number of each type of atom in a molecule of the compound as indicated by the prefixes in the name.
Examples: sulfur dioxide is SO2; dinitrogen pentoxide is N2O5.
B. For ionic compounds:
i. Write the symbol for each element or polyatomic ion.
ii. Determine the charges on the cation and the anion.
iii. If charges are not equal (they do not add to 0), balance the charges to make a neutral formula. To do this, determine
how many of each charged particle must be present to balance out to neutral charge.
iv. Write the formula with subscripts showing how many of each ion is present in the compound.
For polyatomic ions, the same rules apply; if multiple polyatomic ions are needed to balance the formula, use
parentheses to show multiple polyatomic ions in the formula.
Examples:
i. & ii.
iii.
iv.
magnesium oxide
Mg2+ O2(+2) + (-2) = 0
Charges balance.
one Mg and one O
needed for a
neutral compound
MgO
manganese (IV) oxide
Mn4+ O2(+4) + (-2)(2) = 0
Must multiply -2 by 2 for
charges to balance, so two
O2- ions are needed
one Mn and two O needed
for a neutral compound
MnO2
aluminum phosphate
Al3+ PO43(+3) + (-3) = 0
Charges balance.
one Al and one PO4
needed for a neutral
compound
AlPO4
no parentheses
calcium phosphate
Ca2+ PO43(+2)(3) + (-3)(2) = 0
Must multiply +2 by
3 and -3 by 2 for
charges to balance
three Ca and two PO4
needed for a neutral
compound
Ca3(PO4)2
use parentheses to
show two PO4 units
Critical Thinking Question 1: If the compound potassium chloride is written in words, how do you know to write the
formula with only one potassium and one chloride? Could it be KCl2 or K2Cl? Why or why not?
Critical Thinking Question 2: Write the formula for potassium oxide. Why do you not need prefixes in the name?
(e.g. why not name it dipotassium oxide?)
Critical Thinking Question 3: Part A: What is the formula for sulfur dioxide? Sulfur trioxide?
Part B: Why do we need prefixes such as di- and tri- for binary covalent compounds, but not for ionic compounds?
Critical Thinking Question 4: Do the formulas CaOH2 and Ca(OH)2 describe the same compound? Explain.
Lab 5: How Are Ionic and Covalent Compounds Named and Represented Symbolically?
5
Practice Problems
Part A
Use the flow chart on p. 2 and the steps on p. 3 as a guide to name the following compounds from their formulas.
Chemical
Formula
Type of Compound
Circle One
1
SrS
ionic covalent
2
Cs3PO4
ionic covalent
3
P 2O 5
ionic covalent
4
(NH4)2SO4
ionic covalent
5
V 2O 5
ionic covalent
6
ZnI2
ionic covalent
Compound Name
Part B
Use the steps on p. 4 to as a guide to write the formulas for the following compounds from their names.
Compound Name
Type of Compound
Circle One
1
potassium bromide
ionic covalent
2
chromium (IV) chloride
ionic covalent
3
barium nitrate
ionic covalent
4
sodium hydrogen phosphate
ionic covalent
5
dinitrogen tetroxide
ionic covalent
6
silver hydroxide
ionic covalent
Chemical Formula
Instructor Initials ___________
Lab Report
Fill in the report sheet on pages 7 and 8. Use this handout as a guide.
• For each chemical, classify the compound as ionic or covalent.
• Then use the rules for that type of compound to:
− write the formula for the compound if the name is given.
− write the name for the compound if the formula is given.
Turn in the pages specified by your lab instructor.
Grade breakdown for this lab:
5 points: Full participation and completion of the ChemActivity, CTQs and practice problems.
15 points: Completion of the report sheet on pages 7 – 8.
Lab 5: How Are Ionic and Covalent Compounds Named and Represented Symbolically?
Appendix I: Common Polyatomic Ions
*Memorize the polyatomic ions specified by your lecture instructor.
+1 cation
Ion Formula
NH4+
Ion Name
ammonium ion
-1 anions
C2H3O2-
acetate ion
-
CN
ClOClO2ClO3ClO4OH-
cyanide ion
hypochlorite ion
chlorite ion
chlorate ion
perchlorate ion
hydroxide ion
NO3NO2MnO4-
H2PO4-
nitrate ion
nitrite ion
permanganate ion
hydrogen carbonate ion
(also called bicarbonate ion)
dihydrogen phosphate
CO32Cr2O72-
carbonate ion
dichromate ion
SO42SO32HPO42-
sulfate ion
sulfite ion
hydrogen phosphate
PO43PO33-
phosphate ion
phosphite ion
HCO3-
-2 anions
-3 anions
Appendix II: Common Prefixes for Covalent Compounds
1
mono-
2
di-
3
tri-
4
tetra-
5
penta-
6
hexa-
7
hepta-
8
octa-
9
nona-
10
deca-
6
Lab 5: How Are Ionic and Covalent Compounds Named and Represented Symbolically?
Name ____________________________________________________________
Chemical
Formula
Type of Compound
Circle One
1
KCl
ionic covalent
2
SO2
ionic covalent
3
Cr(OH)3
ionic covalent
4
Na3PO4
ionic covalent
5
NH4Br
ionic covalent
6
Cd(C2H3O2)2
ionic covalent
7
Fe2(SO3)3
ionic covalent
8
NaClO4
ionic covalent
9
SnF4
ionic covalent
10
NH4NO3
ionic covalent
11
FeO
ionic covalent
12
CCl4
ionic covalent
13
CaS
ionic covalent
14
CsNO2
ionic covalent
15
SF6
ionic covalent
16
AgMnO4
ionic covalent
17
P4S3
ionic covalent
18
SO3
ionic covalent
19
NaClO
ionic covalent
20
Zn(OH)2
ionic covalent
21
IF7
ionic covalent
22
CuCr2O7
ionic covalent
23
PbS2
ionic covalent
24
Al(HCO3)3
ionic covalent
25
V(CN)4
ionic covalent
Compound Name
7
Lab 5: How Are Ionic and Covalent Compounds Named and Represented Symbolically?
Name ____________________________________________________________
Compound Name
Type of Compound
Circle One
1
ammonium oxide
ionic covalent
2
silver chloride
ionic covalent
3
carbon disulfide
ionic covalent
4
strontium iodide
ionic covalent
5
cobalt (IV) sulfate
ionic covalent
6
barium hydrogen carbonate
ionic covalent
7
xenon tetroxide
ionic covalent
8
cadmium sulfide
ionic covalent
9
copper (II) chlorate
ionic covalent
10
copper (I) chlorate
ionic covalent
11
bromine pentaiodide
ionic covalent
12
magnesium carbonate
ionic covalent
13
lithium phosphate
ionic covalent
14
aluminum perchlorate
ionic covalent
15
iron (III) nitrate
ionic covalent
16
magnesium hydride
ionic covalent
17
sodium hydroxide
ionic covalent
18
nickel (II) sulfate
ionic covalent
19
lead (II) acetate
ionic covalent
20
tin (IV) cyanide
ionic covalent
21
rubidium hypochlorite
ionic covalent
22
sulfur hexafluoride
ionic covalent
23
potassium dichromate
ionic covalent
24
aluminum chlorite
ionic covalent
25
triphosphorus tetraselenide
ionic covalent
Chemical Formula
8