Chapter 5 Flashcards
A mixture
This balloon is filled with a mixture of hydrogen and oxygen gas. The relative amounts of hydrogen and oxygen are variable.
A chemical compound
This balloon is filled with water, composed of molecules that have a fixed ratio of hydrogen to oxygen.
Joseph Proust
formally stated the idea that elements combine in fixed proportions to form compounds.
The law of constant composition states:
All samples of a given compound have the same proportions of their constituent elements.
chemical formula
indicates the elements present in a compound and the relative number of atoms of each.
H2O is the chemical formula for water:
it indicates that water consists of hydrogen and oxygen atoms in a 2:1 ratio.
NaCl for table salt
indicating sodium and chlorine atoms in a 1:1 ratio.
C12H22O11 for table sugar (sucrose),
indicating carbon, hydrogen, and oxygen atoms in a 12:22:11 ratio.
How to List the Elements in Order in Compounds
- 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.
polyatomic ions
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
How to determine the total number of each type of atom in a compound containing a group within parentheses
multiply the subscript outside the parentheses by the subscript for each atom inside the parentheses.
empirical formula
gives the relative number of atoms of each element in a compound.
molecular formula
gives the actual number of atoms of each element in a molecule of the compound.
structural formula
uses lines to represent chemical bonds and shows how the atoms in a molecule are connected to each other.
Pure substances may be
either elements or compounds.
Elements may be
either atomic or molecular.
Compounds may be
either molecular or ionic.
Atomic elements
are those that exist in nature with single atoms as their basic units. Most elements fall into this category.
Molecular elements
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.
Molecular compounds
are compounds formed from two or more nonmetals. The basic units of molecular compounds are molecules composed of the constituent atoms.
Ionic compounds
- 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.
formula unit
The basic unit of ionic compounds
Write formulas for ionic compounds that form from aluminum and oxygen and magnesium and oxygen.
Al3+ O2- Mg2+ O2-
Al2O3 Mg2O2
The first step in naming an ionic compound is identifying it as one.
Remember, any time you have a metal and one or more nonmetals together in a chemical formula, you can assume the compound is ionic.
Categorize Ionic Compounds Depending on the Metal
-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.
Binary compounds
are those that contain only two different elements.
Binary Ionic Compounds with Metal Whose Charge May Vary
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.
Binary Ionic Compounds with Metal Whose Charge May Vary EXAMPLE
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)
Naming Binary Ionic Compounds with Roman Numerals
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
oxyanions
anions containing oxygen.
Acids
are molecular compounds that form ions when dissolved in water.
binary acids
those containing only hydrogen and a nonmetal
oxyacids
those containing hydrogen, a nonmetal, and oxygen.
acids that contain oxyanions—found in the table of polyatomic ions.
Formula Mass
For any compound, the formula mass is the sum of the atomic masses of all the atoms in its chemical formula
