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Chapter 5
Molecules and Compounds

05-06-01un
Title
Anatomy of a chemical formula
Caption
Chemical formulas express which elements have bonded to form a compound. The subscripts express the elements' numerical relationships to one another, as ratios.
Notes
The subscripts are used to represent simple, whole-number ratios among the elements. However, the number "1" is not written, but is implied when a chemical symbol lacks any other subscript. For example, in H2O, there are two H's to one O. The formulas are usually written with the metallic element first, following the order in the periodic table. For example, table salt is NaCl, never ClNa.
Keywords
compound, formula, element, chemical symbol
05-06-02a
Title
Spacefilling models of CO and CO2 molecules
Caption
Spacefilling models reveal the three-dimensional structure of molecules, while expressing the formula.
Notes
The subscript "2" in CO2 tells us that carbon dioxide is a different substance than carbon monoxide, CO.
Keywords
carbon monoxide, carbon dioxide, carbon, oxygen, molecule, covalent, spacefilling, model
05-06-03un
Title
Anatomy of a chemical formula that contains polyatomic ions
Caption
Chemical formulas express which elements have bonded to form a compound. The subscripts express the elements' numerical relationships to one another, as ratios. Polyatomic ions, or groups, (NO3-, in this example) can appear more than once in a formula; if they do, they are set off by parentheses, and the subscript to the right of the parentheses tells how many ions are present.
Notes
The subscripts are used to represent simple, whole-number ratios among the elements. However, the number "1" is not written, but is implied when a chemical symbol lacks any other subscript. For example, in H2O, there are two H's to one O. The formulas are usually written with the metallic element first, following the order in the periodic table. For example, table salt is NaCl, never ClNa. When a polyatomic ion appears more than once in a formula, it is set off by parentheses, followed by a subscript.
Keywords
compound, formula, element, chemical symbol, polyatomic ion
05-07
Title
A molecular view of elements and compounds
Caption
This classification flowchart reveals the categories of pure substances: atoms, molecules, and formula units. Note that both elements and compounds can be molecular.
Notes
The flowchart distinguishes between unbonded elements (atoms), covalently bonded elements and compounds (molecules), and ionically bonded compounds (formula units).
Keywords
compound, formula, element, molecule, formula unit, atom, pure substance
05-10
Title
Elements commonly found as diatomic molecules are shown in yellow
Caption
Elements forming diatomic molecules are all nonmetals. The diatomic molecules are formed by covalent bonding.
Notes
Other elements form polyatomic molecules (e.g., S, P). Students might be sent on a scavenger hunt in reference texts, such as the CRC Handbook of Chemistry and Physics, to find such examples.
Keywords
formula, element, molecule, atom, pure substance, diatomic molecule
05-12-01un
Title
Example of ionic bonding: Al2O3
Caption
Two Al3+ ions and three O2- ions can attract each other to form Al2O3, an ionic compound.
Notes
Students should note that the total of the positive charge (+3 + +3 = +6) has exactly the same magnitude as the total of the negative charge (-2 + -2 + -2 = -6). The compound forms by moving electrons from Al to O, so that the atoms' energy becomes less.
Keywords
alumina, aluminum, oxygen, ionic compound, ion, cation, anion
05-13
Title
Ionic compounds are Type I or Type II, depending on the metal's behavior
Caption
A Type I compound forms when a nonmetal bonds with a metal that forms ions of only a single charge. A Type II compound forms when a nonmetal bonds with a metal that can form ions of multiple charges.
Notes
BaCl2 is an example of a Type I compound: Ba is known to form only the +2 ion. FeCl3 is a Type II compound, because Fe can form either +2 or +3 ions.
Keywords
ionic compound, ion, metal, nonmetal, anion, cation
05-14
Title
The metal element in a Type II compound is generally a transition metal
Caption
Transition metals can display variety in their ion charges. For example, Cu can be +1 or +2; Fe can be +2 or +3.
Notes
Students might be asked to speculate on the reason for the transition metals' ion formation behavior: The highest energy electrons in main group elements are in s and p sublevels, but the highest energy electrons in transition metals are in d and f sublevels.
Keywords
transition metal, element, ion, cation, charge
05-14-01un
Title
Form for naming binary Type II ionic compounds
Caption
The form requires you to know the metal's name, its charge, and the name of the anion. Note that for binary compounds, the anion's name ends in -ide.
Notes
Students may benefit from having a list of commonly found Type II ions provided to them, so that the learning can focus on the naming system, rather than memorizing the ion list.
Keywords
ionic compound, binary, cation, anion, metal, nonmetal
05-14-03un
Title
Form for naming binary Type I ionic compounds
Caption
The form requires you to know the metal's name and the name of the anion. Note that for binary compounds, the anion's name ends in -ide.
Notes
Students should be able to determine the charge of a Type I ion from the metal's location in the periodic table.
Keywords
ionic compound, binary, cation, anion, metal, nonmetal
05-15
Title
An acid can be either a binary acid or an oxyacid
Caption
A binary acid consists of hydrogen and one other nonmetal element; an oxyacid consists of hydrogen, oxygen, and some other element.
Notes
In a binary acid, hydrogen ion (H+) is the cation to a monatomic anion. In an oxyacid, hydrogen ion (H+) is again the cation, but the anion is a polyatomic ion in which one or more oxygen atoms bond with another element.
Keywords
acid, binary, oxyacid, hydrogen ion
05-15-01un
Title
Form for naming binary molecular compounds
Caption
The form requires you to know the name of both elements. The less metallic element's name will be modified to take an -ide suffix. Greek prefixes tell how many atoms of each element are present.
Notes
Binary molecular compounds are identified as compounds made when two nonmetal elements bond covalently.
Keywords
binary, molecular compound, nonmetal
05-15-02un
Title
Form for naming binary acids
Caption
The prefix "hydro" indicates that the acid is a binary acid.
Notes
The "base name" is usually obtained from the first syllable of the nonmetal's elemental name. For example, chlor is the base name for chlorine.
Keywords
acid, binary, hydrogen ion, nonmetal
05-16
Title
Oxyanion names will end with -ite or -ate
Caption
In general, the -ite suffix is reserved for oxyanions with fewer oxygens; the -ate suffix for oxyanions with more oxygens.
Notes
Students will probably have to memorize or consult a table of oxyanions to get the names right.
Keywords
oxyacid, acid, polyatomic ion, hydrogen ion, oxyanion
05-16-01un
Title
Form for naming an oxyacid containing an -ate oxyanion
Caption
Formation of the base name works much the same as for binary acids: The first syllable of the oxyanion name receives an -ic suffix. For example, the nitrate ion yields the base name "nitr", which then takes the -ic suffix, to become "nitric".
Notes
Students will probably have to memorize or consult a table of oxyanions to get the names right.
Keywords
oxyacid, acid, polyatomic ion, hydrogen ion, oxyanion
05-16-02un
Title
Form for naming an oxyacid containing an -ite oxyanion
Caption
Formation of the base name works much the same as for binary acids: The first syllable of the oxyanion name receives an -ous suffix. For example, the nitrite ion yields the base name "nitr", which then takes the -ous suffix, to become "nitrous".
Notes
Students will probably have to memorize or consult a table of oxyanions to get the names right.
Keywords
oxyacid, acid, polyatomic ion, hydrogen ion, oxyanion
05-17
Title
Flowcharts for naming compounds
Caption
This image summarizes the naming forms for the compounds studied in Chapter 5.
Notes
The forms follow three paths: ionic compounds, molecular compounds, and acids.
Keywords
ionic compound, molecular compound, metal, nonmetal, hydrogen ion, binary, oxyanion, oxyacid, polyatomic ion
05-17-01un
Title
Solution map for calculating a formula mass
Caption
The formula mass is the sum of the atomic masses of all the atoms in the chemical formula. The units are amu's.
Notes
This is nothing more than an application of the Law of Conservation of Mass.
Keywords
formula mass, chemical formula, atom, atomic mass

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