Chapter 5

Question 1

A mixture

Answer 1

This balloon is filled with a mixture of hydrogen and oxygen gas. The relative amounts of hydrogen and oxygen are variable.

Question 2

A chemical compound

Answer 2

This balloon is filled with water, composed of molecules that have a fixed ratio of hydrogen to oxygen.

Question 3

Joseph Proust

Answer 3

formally stated the idea that elements combine in fixed proportions to form compounds.

Question 4

The law of constant composition states:

Answer 4

All samples of a given compound have the same proportions of their constituent elements.

Question 5

chemical formula

Answer 5

indicates the elements present in a compound and the relative number of atoms of each.

Question 6

H2O is the chemical formula for water:

Answer 6

it indicates that water consists of hydrogen and oxygen atoms in a 2:1 ratio.

Question 7

NaCl for table salt

Answer 7

indicating sodium and chlorine atoms in a 1:1 ratio.

Question 8

C12H22O11 for table sugar (sucrose),

Answer 8

indicating carbon, hydrogen, and oxygen atoms in a 12:22:11 ratio.

Question 9

How to List the Elements in Order in Compounds

Answer 9

• Chemical formulas list the most metallic elements first. The formula for table salt is NaCl, not ClNa.
• In compounds that do not include a metal, the more metal-like element is listed first.
• Metals are found on the left side of the periodic table and nonmetals on the upper right side.
• Among nonmetals, those to the left in the periodic table are more metal-like than those to the right and are normally listed first. We write NO2 and NO, not O2N and ON.
• Within a single column in the periodic table, elements toward the bottom are more metal-like than elements toward the top. We write SO2, not O2S.

Question 10

polyatomic ions

Answer 10

Some chemical formulas contain groups of atoms that act as a unit. When several groups of the same kind are present, their formula is set off in parentheses with a subscript to indicate the number of that group. Many of these groups of atoms have a charge associated with them

Question 11

How to determine the total number of each type of atom in a compound containing a group within parentheses

Answer 11

multiply the subscript outside the parentheses by the subscript for each atom inside the parentheses.

Question 12

empirical formula

Answer 12

gives the relative number of atoms of each element in a compound.

Question 13

molecular formula

Answer 13

gives the actual number of atoms of each element in a molecule of the compound.

Question 14

structural formula

Answer 14

uses lines to represent chemical bonds and shows how the atoms in a molecule are connected to each other.

Question 15

Pure substances may be

Answer 15

either elements or compounds.

Question 16

Elements may be

Answer 16

either atomic or molecular.

Question 17

Compounds may be

Answer 17

either molecular or ionic.

Question 18

Atomic elements

Answer 18

are those that exist in nature with single atoms as their basic units. Most elements fall into this category.

Question 19

Molecular elements

Answer 19

do not normally exist in nature with single atoms as their basic units. Instead, these elements exist as diatomic molecules—two atoms of that element bonded together—as their basic units.

Question 20

Molecular compounds

Answer 20

are compounds formed from two or more nonmetals. The basic units of molecular compounds are molecules composed of the constituent atoms.

Question 21

Ionic compounds

Answer 21

• When a metal, which has a tendency to lose electrons, combines with a nonmetal, which has a tendency to gain electrons, one or more electrons transfer from the metal to the nonmetal, creating positive and negative ions that are attracted to each other.
• A compound composed of a metal and a nonmetal is considered ionic.
• Unlike molecular compounds, ionic compounds do not contain individual molecules but rather cations and anions in an alternating three-dimensional array.

Question 22

formula unit

Answer 22

The basic unit of ionic compounds

Question 23

Write formulas for ionic compounds that form from aluminum and oxygen and magnesium and oxygen.
Al3+ O2- Mg2+ O2-

Answer 23

Al2O3 Mg2O2

Question 24

The first step in naming an ionic compound is identifying it as one.

Answer 24

Remember, any time you have a metal and one or more nonmetals together in a chemical formula, you can assume the compound is ionic.

Question 25

Categorize Ionic Compounds Depending on the Metal

Answer 25

-The first type (called Type I) contains a metal with an invariant charge—one that does not vary from one compound to another.
-The second type of ionic compound (called Type II) contains a metal with a charge that can differ in different compounds.
Such metals are usually (but not always) found in the transition metals section of the periodic table.
Some transition metals, such as Zn and Ag, form cations with the same charge in all of their compounds: Zn2+, Ag+.
Some main group metals, such as Pb and Sn, form more than one type of cation.

Question 26

Binary compounds

Answer 26

are those that contain only two different elements.

Question 27

Binary Ionic Compounds with Metal Whose Charge May Vary

Answer 27

Since the charge of the metal cation in these types of compounds is not always the same, the charge must be specified in the metal’s name.
We specify the charge with a Roman numeral (in parentheses) following the name of the metal.

Question 28

Binary Ionic Compounds with Metal Whose Charge May Vary EXAMPLE

Answer 28

For example,
we distinguish between Cu+ and Cu2+ by writing a (I) to indicate the 1+ ion or a (II) to indicate the 2+ ion:
Cu+ Copper(I)
Cu2+ Copper(II)

Question 29

Naming Binary Ionic Compounds with Roman Numerals

Answer 29

The name for the compound FeCl3 is the name of the cation, iron, followed by the specific charge of the cation in parentheses (III), followed by the base name of the anion, chlor, with the ending -ide.

The full name is iron(III) chloride.
FeCl3 iron(III) chloride

Question 30

oxyanions

Answer 30

anions containing oxygen.

Question 31

Acids

Answer 31

are molecular compounds that form ions when dissolved in water.

Question 32

binary acids

Answer 32

those containing only hydrogen and a nonmetal

Question 33

oxyacids

Answer 33

those containing hydrogen, a nonmetal, and oxygen.

acids that contain oxyanions—found in the table of polyatomic ions.

Question 34

Formula Mass

Answer 34

For any compound, the formula mass is the sum of the atomic masses of all the atoms in its chemical formula