Ch. 9 - Chemical Names and Formulas
What are some guidelines for helping you name a chemical compound from the chemical formula?
1. Follow the rules for naming acids when H is the first element in the formula. 2. If the compound is binary, generally the name ends with the suffix -ide. If the compound is a molecular binary compound, use prefixes to indicate the number of atoms. 3. When a polyatomic ion that includes oxygen is in the formula, the compound name generally ends in -ite or -ate. 4. If the compound contains a metallic cation that can have different ionic charges, use a Roman numeral to indicate the numerical value of the ionic charge in the compound.
What is the method called that you place a Roman numeral in parentheses after the name of the element to indicate the numerical value of the charge. For example, the cation Fe2+ is named iron(II) ion and is read "iron two ion." The Fe3+ ion is named iron(III) ion and is read "iron three ion."
Stock system
A compound that contains one or more hydrogen atoms and produces hydrogen ions when dissolved in water.
acid
Prefixes in the names of binary molecular compounds help distinguish compounds containing different numbers of ______, such as CO and CO2.
atoms
A ________ is generally an ionic compound that produces hydroxide ions when dissolved in water.
base
How to write the formula of a binary molecular compound....
first use the prefixes in the name to tell you the subscript of each element in the formula. Then, write the correct symbols for the two elements with the appropriate subscripts.
How to write the formula for a compound with a polyatomic ion...
first write the symbol (or formula) for the cation followed by the symbol (or formula) for the anion. Then, add subscripts as needed to balance the charges.
How to write the formula for a base?
first write the symbol for the metal cation followed by the formula for the hydroxide ion. Then, balance the ionic charges just as you would for any ionic compound.
Dalton postulated that atoms combine in simple whole-number ratios. If the ratio of atoms of each element in a compound is fixed, then it follows that the ratio of their masses is also....
fixed
When the formula for a polyatomic ion begins with H, you can think of the H as representing a ....
hydrogen ion (H+) combined with another polyatomic ion. For example, HCO₃⁻ is a combination of H+ and CO₃ ²⁻.
Anion names start with the stem of the element name and end in... For example, two elements in Group 7A are fluorine and chlorine. The anions for these nonmetals are....
ide the fluoride ion (F-) and the chloride ion (Cl-).
Acids are a group of ____________________ with unique properties.
ionic compounds
Binary compounds can be _________ compounds or _________ compounds. If you know the name of a binary ionic compound, you can write the ____________.
ionic or molecular formula
Whenever the same two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers. This is called....
law of multiple proportions
Binary ionic compounds are composed of two elements, a...
metal and a nonmetal.
CO is named carbon ____________ and CO2 is named carbon ____________.
monoxide and dioxide
An older, less useful method for naming these cations uses a root word based on the classical name of the element with different suffixes at the end of the word. • The suffix -ous is used to.... • The suffix -ic is used....
name the cation with the lower of the two ionic charges. with the higher of the two ionic charges.
Binary molecular compounds are composed of two...
nonmetals.
Whenever more than one polyatomic ion is needed to balance the charges in an ionic compound, use ____________ to set off the polyatomic ion in the formula.
parentheses
To name any binary ionic compound....
place the cation name first, followed by the anion name. For example, the name of NaBr is sodium bromide, and the name of SrF₂ is strontium fluoride.
A few transition metals have only one ionic charge. The names of these cations do not have a Roman numeral. These exceptions include.....
silver, with cations that have a 1+ charge (Ag+), as well as cadmium and zinc, with cations that have a 2+ charge (Cd2+ and Zn2+).
Before the science of chemistry developed, compounds were often named to describe...
some property of the substance or its source.
To name a compound containing a polyatomic ion,...
state the cation name first and then the anion name. If the cation is a metallic element that has more than one common ionic charge, include a Roman numeral in the cation name.
The French chemist Antoine-Laurent Lavoisier (1743-1794) found...
that it was becoming impossible to memorize all the unrelated names of the compounds.
The charges of the cations of many transition metal ions must be determined from...
the number of electrons lost.
Recall from Ch. 7 that you can use the crisscross method to write a formula unit. In this method, the numerical value of the charge of each ion is crossed over and becomes the subscript for....
the other ion.
Two laws—the law of definite proportions and the law of multiple proportions— describe....
the proportions in which elements combine to form compounds.
A binary compound is composed of...
two elements.
How to write the formula for an acid....
use the rule for writing the name of the acid in reverse. Then, balance the ionic charges just as you would for any ionic compound.
Binary molecular compounds are composed of molecules, so ionic charges cannot be used to....
write formulas or to name them.
Ionic compounds consist of a positive metal ion (cation) and a negative nonmetal ion (anion) combined in amounts that cause their charges to add up to....
zero.
The net ionic charge of the formula must be....
zero.
How can you tell which of the cations forms the compound CuO?
• The formula indicates that the copper cation and oxide anion combine in a 1:1 ratio. • The oxide anion always has a 2- charge. • Therefore, the charge of the copper cation must be 2+ in order to balance the 2- charge.
Aluminum hydroxide consists of the aluminum cation (Al³⁺) and the hydroxide anion (OH-). You need three hydroxide ions to balance the 3+ charge of the aluminum cation. Thus, the formula for aluminum hydroxide is....
Al(OH)₃
How are bases named?
Bases are named in the same way as other ionic compounds—the name of the cation is followed by the name of the anion.
Explain how to determine charges of monatomic ions.
Cations: The names of the cations of Group 1A, Group 2A, and Group 3A metals are the same as the name of the metal, followed by the word ion or cation. (Thus, Na+ is the sodium ion (or cation).) Anions: Nonmetals tend to gain electrons to form anions, so the charge of a nonmetallic ion is negative. The charge of any ion of a Group A nonmetal is determined by subtracting 8 from the group number. (The elements in Group 7A form anions with a 1- charge (7 - 8 = -1).)
Consider hydrobromic acid. Rule 1 states: When the name of the anion ends in -ide, the acid name begins with the prefix hydro-. The stem of the anion has the suffix -ic and is followed by the word acid. Hydrobromic acid (hydro- prefix and -ic suffix) must be a combination of hydrogen ion (H+) and bromide ion (Br-). The formula is....
HBr
When naming an acid, think of it as an anion combined with as many hydrogen ions as needed to make the molecule electrically neutral. Therefore, the chemical formulas of acids are in the general form....
HnX
What is the formula for sulfuric acid? Rule 3 states: When the anion name ends in -ate, the acid name is the stem of the anion with the suffix -ic, followed by the word acid. Sulfuric acid (-ic ending) must be a combination of hydrogen ion and sulfate ion (SO₄²⁻).
H₂SO₄ because two hydrogen ions are needed to balance the 2- charge of the sulfate anion.
How do you write the formula for phosphorous acid? Rule 2 states: When the anion name ends in -ite, the acid name is the stem of the anion with the suffix -ous, followed by the word acid. The hydrogen ion and phosphite ion (PO₃ ³⁻) must be the components of phosphorous acid. You need three hydrogen ions to balance the 3- charge of the phosphite ion.
H₃PO₃
The ionic compound potassium chloride is composed of potassium cations (K+) and chloride anions (Cl-), so potassium chloride is a binary ionic compound. The charge of each K+ cation is balanced by the charge of each Cl- anion in a 1:1 ration, so the formula for potassium chloride is...
KCI
Which law does the following describe? • A chemical formula tells you, by means of subscripts, the ratio of atoms of each element in the compound. • Ratios of atoms can also be expressed as ratios of masses. • For example, magnesium sulfide (MgS) is composed of magnesium cations and sulfide anions.
Law of Definite Proportions
The following describes... • Two familiar compounds, water (H₂O) and hydrogen peroxide (H₂O₂), are formed by the same two elements. • They have different physical and chemical properties. • For example, hydrogen peroxide bleaches the dye in most fabrics, but water does not. • Both water and hydrogen peroxide obey the law of definite proportions.
Law of Multiple Proportions
___________________ consist of a single atom with a positive or negative charge.
Monatomic ions
In writing a chemical formula from a chemical name, it is helpful to remember the following guidelines.
Prefixes in a name generally indicate that the compound is molecular.
An interesting example of a Binary Molecular Compound is tetraphosphorus trisulfide, which is used in some matches. The name tetraphosphorus trisulfide has the prefixes tetra- and tri-, so the subscripts of phosphorus and sulfur must be 4 and 3, respectively. Thus, the formula for tetraphosphorus trisulfide is.....
P₄S₃.
If the metallic element in a binary ionic compound has more than one common ionic charge, a.....
Roman numeral must be included in the cation name.
Know how to do all the sample problems throughout Chapter 9.
......
mono-
1
Three rules can help you name an acid with the general formula HnX dissolved in water.
1. When the name of the anion ends in -ide, the acid name begins with the prefix hydro-. The stem of the anion has the suffix -ic and is followed by the word acid. (HCl (X= chloride) is named hydrochloric acid.) 2. When the anion name ends in -ite, the acid name is the stem of the anion with the suffix -ous, followed by the word acid. (Thus, H₂SO₃ (X = sulfite) is named sulfurous acid.) 3. When the anion name ends in -ate, the acid name is the stem of the anion with the suffix -ic, followed by the word acid. (Thus, HNO₃ (X = nitrate) is named nitric acid.)
How to name a binary molecular compound?
1. Write the names of the elements in the order listed in the formula. 2. Use prefixes appropriately to indicate the number of each kind of atom. If just one atom of the first element is in the formula, omit the prefix mono- for that element. Also, the vowel at the end of a prefix is sometimes dropped when the name of the element begins with a vowel. 3. End the name of the second element with the suffix -ide.
deca-
10
di-
2
If a sample of hydrogen peroxide has the same amount of hydrogen as a sample of water, the ratio of the amount of oxygen in the two compounds is exactly...
2:1
tri-
3
tetra-
4
penta-
5
hexa-
6
hepta-
7
octa-
8
nona-
9
Iron(III) oxide contains Fe3+ cations combined with oxide anions (O2-). To balance a 3+ charge and a 2- charge, you must find the least common multiple of the charges, which is 6. The balanced formula is......
Fe₂O₃
How to write the formula of a binary ionic?
First write the symbol of the cation and then the anion. Then add subscripts as needed to balance the charges.
When two nonmetallic elements combine, they often do so in more than one way. For example....
The elements carbon and oxygen combine to form CO and CO₂.
What is a major disadvantage of using classical names for ions?
They do not tell you the actual charge of the ion.
How many methods are used to name ions that can have more than one common ionic charge?
Two
Explain how polyatomic ions differ from and are similar to monatomic ions.
Unlike a monatomic ion, a polyatomic ion is composed of more than one atom. But like a monatomic ion, a polyatomic ion behaves as a unit and carries a charge.