1. Introductory Chemistry, 2nd Edition Nivaldo Tro
Chapter 5
Molecules and
Compounds

2. Molecules and Compounds
Compounds = composed of 2 or more elements chemically combined
Properties completely different from component elements
Salt
Sodium (Na) – shiny, reactive, poisonous
Chlorine (Cl) – pale yellow gas, reactive, poisonous
Sodium chloride (NaCl) – table salt, flavor enhancer
Tro's Introductory Chemistry, Chapter 5

3. Law of Constant Composition
Pure substances have constant composition
all samples of a pure substance contain same elements in same ratios or proportions regardless of source
mixtures have variable composition
Tro's Introductory Chemistry, Chapter 5

4. Compounds Display Constant Composition
Water (H2O) decomposed by electrolysis yields 16.0 grams of oxygen to every 2.00 grams of hydrogen.
Water has a constant Mass Ratio of Oxygen to Hydrogen of 8.0.
Tro's Introductory Chemistry, Chapter 5

5. Formulas Describe Compounds
Compound = a distinct substance that is composed of atoms of two or more elements
Formulas give the number and type of each atom in the simplest unit of the compound
Molecules (H2O) or ions (CaCl2)
Number of atoms of each element is written to the right of the element as a subscript
if only one atom, 1 subscript is not written
Polyatomic groups are placed in parentheses
if more than one, i. e. Ca(NO3)2
Tro's Introductory Chemistry, Chapter 5

6. Formulas Describe Compounds
Examples:
water = H2O \ two atoms of hydrogen and 1 atom of oxygen
table sugar (sucrose) = C12H22O11 \12 atoms of C, 22 atoms of H and 11 atoms O
Tro's Introductory Chemistry, Chapter 5

7. Classifying Materials
Atomic elements = elements whose particles are single atoms; Na, Ne, Hg, Ag
Molecular elements = elements whose particles are multi-atom molecules; H2, O2, N2, Cl2
Tro's Introductory Chemistry, Chapter 5

8. Molecular Elements H2 Cl2 Br2 I2 N2 O2 F2
Certain elements occur as 2 atom molecules
Rule of 7’s
there are 7 common diatomic elements
find the element with atomic number 7, N
make a figure 7 by going over to Group 7A, then down
don’t forget to include H2 H2
Cl2
Br2 I2
VIIA
N2 O F2 7

9. Classifying Materials
Molecular compounds = compounds whose particles are molecules made of only nonmetals, i.e. CO2
Ionic compounds = compounds whose particles are cations (+) and anions (-), i.e. NaCl
Tro's Introductory Chemistry, Chapter 5

10. Tro's Introductory Chemistry, Chapter 5
Molecular Compounds
Two or more nonmetals, i.e. H2O, CO2, C6H12O6
Smallest unit is a molecule
Tro's Introductory Chemistry, Chapter 5

11. Order of Elements in a Formula
Metals written first
NaCl
Nonmetals written in order from Table 5.1
CO2
occasional exceptions for historical or informational reasons
H2O, but NaOH
Order of Listing Nonmetals
in Chemical Formulas
Table 5.1 F O Cl Br I S H N P C
Tro's Introductory Chemistry, Chapter 5

12. Tro's Introductory Chemistry, Chapter 5
Ionic Compounds
Metals + nonmetals
No individual molecule units, instead have a 3-dimensional array of cations and anions made of formula units
Tro's Introductory Chemistry, Chapter 5

13. Molecular View of Elements and Compounds

14. Tro's Introductory Chemistry, Chapter 5
Classify each of the following as either an atomic element, molecular element, molecular compound or ionic compound
aluminum, Al
aluminum chloride, AlCl3
chlorine, Cl2
acetone, C3H6O
carbon monoxide, CO
cobalt, Co
Tro's Introductory Chemistry, Chapter 5

15. Tro's Introductory Chemistry, Chapter 5
Classify each of the following as either an atomic element, molecular element, molecular compound or ionic compound
aluminum, Al = atomic element
aluminum chloride, AlCl3 = ionic compound
chlorine, Cl2 = molecular element
acetone, C3H6O = molecular compound
carbon monoxide, CO = molecular compound
cobalt, Co = atomic element
Tro's Introductory Chemistry, Chapter 5

16. Major Classes of Compounds
Ionic
metal + nonmetal
metal first in formula
Binary Ionic
compounds with polyatomic ions
Molecular
2 nonmetals
Binary Molecular (or Binary Covalent)
Acids – formula starts with H
though acids are molecular, they behave as ionic when dissolved in water
may be binary or oxyacid
Tro's Introductory Chemistry, Chapter 5

17. Binary Ionic Compounds: Writing a correct formula
1. Write down the charges of the stable ions with the positive ion first.
Ex: for Chlorine and magnesium
Mg Cl 2+ 1-

18. 2. Cross-over charges to get subscripts. Drop all +/- signs.
Ex: for Chlorine and magnesium
Mg Cl 2+
1 - 1 2

19. 3. Reduce/Simplify subscripts to get the lowest whole number ratio
3. Reduce/Simplify subscripts to get the lowest whole number ratio. The subscript “1” does not have to be shown.
Ex: for Chlorine and magnesium
MgCl2
Ex: calcium and sulfur
Ca+2S-2
Ca2S2
cross-over
CaS
simplify

20. How many electrons will an atom lose or gain in an ionic compound?
lose 1 e-
lose 2 e-
lose 3 e-
gain 3 e-
gain 2 e-
gain 1 e-

21. What will be the charge on the “stable ion” formed?+1 +2 +3 -3 -2 -1

22. Rules for Naming Ionic Compounds from Formula
Made of cation and anion
Name by simply naming the ions
If cation is:
Type I metal (main group) = metal name
Type II metal (transition element) = metal name(charge)
Polyatomic ion = name of polyatomic ion
If anion is:
Nonmetal = root of nonmetal name + ide
Tro's Introductory Chemistry, Chapter 5

23. How do you know a metal cation is Type II?
Metal Cations
Type I
metals whose ions can only have one possible charge
IA, IIA, (Al, Ga, In)
determine charge by position on the Periodic Table
IA = +1, IIA = +2, (Al, Ga, In = +3)
Type II
metals whose ions can have more than one possible charge (transition elements)
determine charge by charge on anion
How do you know a metal cation is Type II?
its not Type I !!!
Tro's Introductory Chemistry, Chapter 5

24. Tro's Introductory Chemistry, Chapter 5
Determine if the following metals are Type I or Type II. If Type I, determine the charge on the cation it forms.
lithium, Li
copper, Cu
gallium, Ga
tin, Sn
strontium, Sr
Tro's Introductory Chemistry, Chapter 5

25. Tro's Introductory Chemistry, Chapter 5
Determine if the following metals are Type I or Type II. If Type I, determine the charge on the cation it forms.
lithium, Li Type I +1
copper, Cu Type II
gallium, Ga Type I +3
tin, Sn Type II
strontium, Sr Type I +2
Tro's Introductory Chemistry, Chapter 5

26. Determining Charge and Naming Monatomic Nonmetal Anions
Determine the charge from position on the Periodic Table
To name anion, change ending on the element name to –ide
4A = -4
5A = -3
6A = -2
7A = -1
C = carbide
N = nitride
O = oxide
F = fluoride
Si = silicide
P = phosphide
S = sulfide
Cl = chloride
Tro's Introductory Chemistry, Chapter 5

27. Naming Type I Binary Ionic Compounds
Contain Metal Cation + Nonmetal Anion
Metal listed first in formula & name
name metal cation first, name nonmetal anion second
cation name is the metal name
nonmetal anion named by changing the ending on the nonmetal name to -ide

28. What is the correct formula and name for a compound made from:
1. nitrogen and potassium
2. magnesium and oxygen
3. chlorine and calcium
4. oxygen and aluminum

29. 1. nitrogen and potassium
K3N potassium nitride
2. magnesium and oxygen
MgO magnesium oxide
3. chlorine and calcium
CaCl2 calcium chloride
4. oxygen and aluminum
Al2O3 aluminum oxide

30. Naming Type II Binary Ionic Compounds
Name metal cation first, name nonmetal anion second
Metal cation name is the metal name followed by a Roman Numeral in parentheses to indicate its charge
determine charge from anion charge
Common Type II cations in Table 5.5
Nonmetal anion named by changing the ending on the nonmetal name to -ide
Tro's Introductory Chemistry, Chapter 5

31. Example – Naming Binary Ionic, Type II Metal CuCl
Identify Major Class
Cu = metal, on left side of Periodic Table
Cl = nonmetal, on right side of Periodic Table
 Ionic
Identify the Subclass 2 elements,
 Binary Ionic
Is the metal Type I or Type II
Cu not in Group IA, IIA, or (Al, Ga, In)  Type II
Tro's Introductory Chemistry, Chapter 5

32. Example – Naming Binary Ionic, Type II Metal CuCl
Identify cation and anion
Cl = Cl- because it is Group 7
Cu = Cu+ to balance the charge
Name the cation
Cu+ = copper(I)
Name the anion
Cl- = chloride
Write the cation name first, then the anion name
copper(I) chloride
Tro's Introductory Chemistry, Chapter 5

33. Give the formula and name for a compound from Cu+1 and sulfur
Cu+1 S-2
formula = Cu2S
name = copper(I) sulfide

34. name = iron(II) chloride
Give the formula and name for a compound from Fe+2 and chlorine
Fe+2 Cl-1
formula = FeCl2
name = iron(II) chloride
Give the formula and name for a compound from Cu+2 and sulfur
Cu+2 S-2
formula = CuS
name = copper(II) sulfide

35. What is the formula for copper(II) oxide?
Cu+2 O-2
formula = CuO

36. Compounds with Polyatomic Ions
Polyatomic ions are single ions that contain more than one atom
Formula: cation first, polyatomic anion or polyatomic cation, monatomic anion
Name cation first and then anion
Non-polyatomic cations named like Type I and II
Non-polyatomic anions named with –ide
Polyatomic ions = use name of polyatomic ion
Tro's Introductory Chemistry, Chapter 5

37. Some Common Polyatomic Ions (be able to recognize these)
Name
Formula and Charge
acetate
C2H3O2–
carbonate
CO32–
hydrogen carbonate
(aka bicarbonate)
HCO3–
hydroxide
OH–
nitrate
NO3–
nitrite
NO2–
sulfate
SO42–
chlorate
ClO3–
ammonium
NH4+
Tro's Introductory Chemistry, Chapter 5

38. Naming Ionic Compounds with Polyatomic Ion Na2SO4
Identify Major Class
Na = metal, on the left side of Periodic Table
SO4 = is a polyatomic ion,  Ionic
Identify the Subclass
compound has 3 elements  Ionic with Polyatomic Ion
Is the metal Type I or Type II
Na is in Group IA,  Type I
Tro's Introductory Chemistry, Chapter 5

39. Naming Ionic Compounds with Polyatomic Ion Na2SO4
Identify the ions
Na = Na+ because in Group 1
SO4 = SO42- a polyatomic ion
Name the cation
Na+ = sodium (Type I)
Name the anion
SO42- = sulfate
Write the name of the cation followed by the name of the anion
sodium sulfate
Tro's Introductory Chemistry, Chapter 5

40. Naming Ionic Compounds with Polyatomic Ion Fe(NO3)3
Identify Major Class
Fe = metal, on left side of Periodic Table
NO3 = is a polyatomic ion because it is in ( )
 Ionic
Identify the Subclass
Have 3 elements  Ionic with Polyatomic Ion
Is the metal Type I or Type II
Fe not in Group IA, IIA, or (Al, Ga, In)  Type II
Tro's Introductory Chemistry, Chapter 5

41. Naming Ionic compounds with Polyatomic Ion Fe(NO3)3
Identify the ions
NO3 = NO3- a polyatomic ion
Fe = Fe+3 to balance the charge of the 3 NO3-1
Name the cation
Fe+3 = iron(III) (Type II)
Name the anion
NO3- = nitrate
Write the name of the cation followed by the name of the anion
iron(III) nitrate
Tro's Introductory Chemistry, Chapter 5

42. Rules for Naming Binary Molecular Compounds
Binary molecular compounds = composed of 2 nonmetal elements
for binary molecular compound:
name first nonmetal
then name second nonmetal with ide ending
then give each name a prefix to indicate number of atoms (subscript) of each element in formula
Tro's Introductory Chemistry, Chapter 5

43. Naming Binary Molecular Compounds
Name first element in formula first
use the full name of the element
Name the second element in the formula with an -ide
as if it were an anion, however, remember these compounds do not contain ions!
Use a prefix in front of each name to indicate the number of atoms
Never use the prefix mono- on the first element

44. Tro's Introductory Chemistry, Chapter 5
Subscript - Prefixes
1 = mono-;
not used on first nonmetal
2 = di-
3 = tri-
4 = tetra-
5 = penta-
6 = hexa-
7 = hepta-
8 = octa-
drop last “a” if name begins with vowel
Tro's Introductory Chemistry, Chapter 5

45. Naming Binary Molecular Compounds BF3
Identify Major Class
B = nonmetal, on right side of Periodic Table
F = nonmetal, on right side of Periodic Table
 Molecular
Identify the Subclass
2 elements  Binary Molecular
Tro's Introductory Chemistry, Chapter 5

46. Naming Binary Molecular Compounds BF3
Name the first element: boron
Name the second element with an –ide
fluorine  fluoride
Add a prefix to each name to indicate the subscript
monoboron, trifluoride
Write the first element with prefix, then the second element with prefix
Drop prefix mono from first element
boron trifluoride
Tro's Introductory Chemistry, Chapter 5

47. Tro's Introductory Chemistry, Chapter 5
Formula Mass
Formula mass = mass of an individual molecule or formula unit
also known as molecular mass or molecular weight
Sum of the masses of the atoms in a single molecule or formula unit
whole = sum of the parts!
mass of 1 molecule of H2O
= 2(1.01 amu H) amu O = amu
Tro's Introductory Chemistry, Chapter 5