chemistry

Naming Chemical Substances & Writing Chemical Formulas

Purpose:

The purpose of this lab is to name ionic compounds, molecular compounds and aqueous acids from chemical formulas. Chemical formulas will also be derived from substance names.

Introduction to Nomenclature:

1) Chemists have developed a systematic way of naming chemical substances.

2) Most substances discussed in introductory chemistry classes are inorganic (made up of elements other than carbon).

3) The first step in naming a substance is to determine if it is an ionic compound, a molecular compound or an aqueous acid.

a. An ionic compound contains a metal cation and a nonmetal anion.

i. Most cations are metal ions.

1. Hydrogen (H+) and the ammonium ion (NH4+) are exceptions.

ii. Anions are usually made of one or more nonmetal ions.

1. Hydrogen can also be an anion, when grouped with a metal, like CaH2 (calcium hydride).

2. Most polyatomic ions are anions (ClO3-).

iii. Sodium chloride (NaCl) is an example of an ionic compound. The sodium (a metal) is the cation (Na+) and the Cl (a nonmetal) is the anion (Cl-).

b. A molecular compound (or a covalent compound) contains two or more nonmetals.

i. Carbon dioxide (CO2) is an example of a molecular compound. The carbon and oxygen are both nonmetals.

c. An aqueous acid contains hydrogen and an anion. Acids are easy to identify, as the hydrogen is usually first in the chemical formula.

i. Hydrochloric acid (HCl) is an example of an aqueous acid.

Naming Binary Ionic Compounds:

1) When naming a binary ionic compound, where the metal can form only one charge of ion, name the cation first and then the non-metal stem + -ide.

a. For example, Al2S3 is aluminum sulfide.

metal – aluminum; non-metal – sulfur, which becomes

sulf- + -ide

2) When naming a binary ionic compound, where the metal can form ions with different charges, name the metal first, place the charge of the metal in parentheses (using Roman numerals) and then the non-metal + -ide.

a. For example, FeBr3 is iron (III) bromide.

i. Iron in its ionic form can exist as Fe+2 or Fe+3.

ii. The sum of the charges for a neutral ionic compound equal zero. This compound contains one iron ion and three bromide ions. The charge for bromide is -1. Algebra can be used to determine the charge for iron.

Fe + 3 Br = 0

Fe + 3 (-1) = 0

Fe = +3

Naming Ternary Ionic Compounds:

1) When naming a ternary ionic compound, where the metal forms an ion of one charge, name the cation first and then the polyatomic ion. Do not change the formula or ending of the polyatomic ion for ionic compounds.

a. For example, Ca(OH)2 is calcium hydroxide.

Metal – calcium; Polyatomic ion – hydroxide

b. Another example, Na2CO3 is sodium carbonate.

Metal – sodium; Polyatomic ion – carbonate

2) When naming a ternary ionic compound, where the metal can form ions with different charges, name the metal first, place the charge of the metal in parentheses (using Roman numerals) and then the polyatomic ion.

a. For example, Co(ClO3)2 is cobalt (II) chlorate.

i. Cobalt in its ionic form can exist as Co+2 or Co+3.

ii. The sum of the charges for a neutral ionic compound equal zero. This compound contains one cobalt ion and two chlorate ions. The charge for chlorate is -1. Algebra can be used to determine the charge for iron.

Co + 2 ClO3 = 0

Co + 2 (-1) = 0

Co = +2

Naming Binary Molecular Compounds:

1) When naming a molecular compound (two nonmetals), Greek prefixes are used to indicate the number of each atom.

Prefix	Number of Atoms	Prefix	Number of Atoms
mono -	1	hexa-	6
di-	2	hepta-	7
tri-	3	octa-	8
tetra-	4	nona-	9
penta-	5	deca-	10

For the first element, name the Greek prefix + element name. For the second element, name the Greek prefix + element name stem + -ide

a. If only one atom is present for the first element, omit mono-.

b. For example, PCl3 is phosphorous (no need for mono-) trichloride

c. Another example, Cl2O7 is dichlorine heptoxide. Since hepta- ends in a vowel and oxide begins with a vowel, the “a” in hepta- can be dropped.

Naming Binary Acids:

1) When naming a binary aqueous acid, use the prefix “hydro-“ + the nonmetal stem + the suffix “–ic acid”.

a. For example, HF is hydrofluoric acid.

b. Another example, H2S is hydrosulfuric acid.

Naming Ternary Acids (Oxoacids/Oxyacids):

1) When naming a ternary aqueous acid, also known as an oxyacid,

the name depends on the anion from which it forms. If the anion ends in “-ate”, replace the “-ate” with “-ic acid”. If the anion ends in “-ite”, replace the “-ite” with “-ous acid”.

a. For example, H2CO3 is carbonic acid. The two ions present are H+ and CO3-2. The ion CO3-2 is carbonate; therefore, the acid is carbonic acid.

b. Another example, HNO2 is nitrous acid. The two ions present are H+ and NO2-. The ion NO2- is nitrite; therefore, the acid is nitrous acid.

Introduction to Writing Chemical Formulas

1) Ionic compounds are composed of a cation and an anion. The chemical formula will contain the symbol/formula and number of each ion. The sum of the charges of the cation must equal the sum of the charges of the anion.

a. For ionic compounds, the crossover rule is used in writing formulas.

b. The charge for the anion becomes the subscript of the cation and the charge for the cation becomes the subscript for the anion. If the subscript is a 1, no number is written.

c. Do not bring down the + and – signs, just the numbers.

d. For example, the chemical formula for aluminum oxide is Al2O3. The aluminum ion is Al+3 and the oxide ion is O-2. The crossover rule yields Al2O3.

e. The crossover rule is also used for compounds containing a polyatomic ion.

f. For example, the chemical formula for iron (II) nitrate is Fe(NO3)2. The iron (II) ion is Fe+2 and the nitrate ion is NO3-. The crossover rule yields Fe(NO3)2.

g. Parentheses must be used if a subscript is needed to indicate more than one polyatomic ion is present.

h. In addition, the lowest ratio of elements must be present.

i. For example, magnesium oxide is MgO, rather than Mg2O2. Aluminum phosphate is AlPO4, rather than Al3(PO4)3.

2) Molecular compounds are composed of two or more nonmetals. The chemical formula is derived from the name of the compound. The Greek prefixes indicate the number of each atom present.

a. For example, dinitrogen tetroxide is N2O4.

b. Another example, nitrogen monoxide is NO.

3) Aqueous acids contain hydrogen and an anion.

a. Acids containing both “hydro-“ and “–ic acid” are binary acids. One element is hydrogen and the other is a single nonmetal. The crossover rule also applies for acids.

i. For example, the formula for hydrochloric acid is HCl. The formula is derived from H+ and Cl-.

b. Acids containing just “–ic acid” are oxyacids from polyatomic ions ending in “-ate”.

i. For example, the formula for chromic acid is H2CrO4. The formula is derived from H+ and CrO4-2.

c. Acids containing “–ous acid” are oxyacids from polyatomic ions ending in “-ite”.

i. For example, the formula for chlorous acid is HClO2. The formula is derived from H+ and ClO2-.

Procedure:

Part 1

1) Classify the following substances as an ionic compound, a molecular compound or an aqueous acid.

2) Provide the correct name of each substance.

Part 2

1) Classify the following substances as an ionic compound, a molecular compound or an aqueous acid.

2) Provide the correct chemical formula of each substance.

Part 3

1) Provide the correct name of each substance.

2) Explain why the information provided is incorrect.

Part 4

1) Provide the correct chemical formula of each substance.

2) Explain why the information provided is incorrect.

Conclusion

1. What is the difference between an ionic compound and a molecular compound? How can one identify an acid?

2. Which substances use the Stock system for naming compounds?

3. What is the difference between acids ending in “-ous” and acids ending in “-ic” ?

4. What is the difference between hydrochloric acid, perchloric acid, chloric acid, chlorous acid and hypochlorous acid?

5. Create your own flow chart for naming compounds. It should include ionic compounds, molecular compounds and aqueous acids. Be sure to include the different systems used in naming ionic compounds, the omission of “mono-“ for molecular compounds and the different systems for naming acids.

The lab must be completed and turned in before you leave.

Data Tables

Part 1

Substance	Classification	Name
CCl4
KBr
HCl
LiNO3
CuF
(NH4)2SO4
H2CO3
N2O4
Fe(CN)2
NH4I
HNO2
MgO
P4S3
HClO
Pb(ClO4)2
H2S (aq)
CoN
CrI3
Ag3PO4
PCl5
HC2H3O2
Cl2O7
HBr
Sn(ClO2)4
H2SO3
Zn3P2
HgSe
NO
H2CrO4
Ca(OH)2

Part 2

Substance	Classification	Chemical Formula
chloric acid
carbon monoxide
cobalt (II) chloride
sodium bicarbonate
ammonium chromate
sulfurous acid
diphosphorous pentasulfide
copper (II) nitrite
potassium permanganate
perchloric acid
strontium iodide
hydrofluoric acid
diboron tetrachloride
chromium (II) phosphate
chlorous acid
phosphorous triiodide
cadmium sulfide
hydroiodic acid
mercury (I) oxide
lead (IV) carbonate
ammonium sulfite
aluminum bromide
dichlorine monoxide
nitric acid
tin (IV) sulfate
sulfur hexafluoride
nitrous acid
iron (III) iodide
lithium dichromate
dioxygen difluoride

Part 3

Substance	Incorrect Name	Correct Name	Explanation
PbI2	lead iodide
Mg(NO3)2	magnesium (II) nitrate
P2O3	diphosphorous oxide
H2CO3	hydrocarbonic acid
CI4	carbon (IV) iodide

Part 4

Name	Incorrect Chemical Formula	Correct Chemical Formula	Explanation
calcium sulfate	CaSO3
carbon tetrabromide	CBr3
aluminum chlorate	Al(ClO4)3
nitrous acid	H2NO2
barium sulfide	BaS2

Introductory Chemistry Lab

Jones