1. Chapter 2 Atoms, Molecules, and Ions
General Chemistry: An Integrated Approach Hill, Petrucci, 4th Edition
Chapter 2 Atoms, Molecules, and Ions
Mark P. Heitz
State University of New York at Brockport
© 2005, Prentice Hall, Inc.

2. Laws of Chemical Composition
Conservation of Mass - The total mass remains constant during a chemical reaction.
Example: Decomposition of mercuric oxide (HgO)
EOS
HgO(s) = Hg(l) + O2(g)
Chapter 2: Atoms, Molecules, and Ions

3. Law of Definite Proportions
All samples of a compound have the same composition; that is, all samples have the same proportions, by mass, of the elements present
EOS
Water always contains:
~89% oxygen
~11% hydrogen
Chapter 2: Atoms, Molecules, and Ions

4. Basic Copper Carbonate
EOS
Chapter 2: Atoms, Molecules, and Ions

5. Law of Multiple Proportions
When two or more different compounds of the same two elements are compared, the masses of one element that combine with the a fixed mass of the second element are in the ratio of small whole numbers.
Multiple proportions illustrated
EOS
Chapter 2: Atoms, Molecules, and Ions

6. Law of Multiple Proportions
EOS
Chapter 2: Atoms, Molecules, and Ions

7. Atomic Theory of Matter
All matter is composed of extremely small, indivisible particles called atoms
All atoms of a given element are alike in mass and other properties, but atoms of one element differ from the atoms of every other element
Compounds are formed when atoms of different elements unite in fixed proportions
A chemical reaction involves a rearrangement of atoms. No atoms are created, destroyed, or broken apart in a chemical reaction
EOS
Chapter 2: Atoms, Molecules, and Ions

8. Atomic Theory Illustrated …
Note the laws of constant composition and conservation of mass
EOS
Chapter 2: Atoms, Molecules, and Ions

9. Chapter 2: Atoms, Molecules, and Ions
Subatomic Particles
Protons and neutrons are located at the center of an atom called the nucleus.
Electrons are dispersed around the nucleus.
EOS
Chapter 2: Atoms, Molecules, and Ions

10. Chapter 2: Atoms, Molecules, and Ions
Isotopes
Atoms that have the same number of protons but different numbers of neutrons are called isotopes
Atomic number (Z) = number of protons
Hydrogen has 1 proton, 0 neutrons - Z = 1
Deuterium has 1 proton, 1 neutron - Z = 1
Tritium has 1 proton, 2 neutrons - Z = 1
EOS
Chapter 2: Atoms, Molecules, and Ions

11. Other Examples of Isotopes
Carbon-14 Z = 6 so 8 neutrons
Chlorine-35 Z = 17 so 18 neutrons
Uranium Z = 92 so 142 neutrons
EOS
The number of neutrons = A – Z
Chapter 2: Atoms, Molecules, and Ions

12. Chapter 2: Atoms, Molecules, and Ions
Atomic Masses
EOS
Chapter 2: Atoms, Molecules, and Ions

13. Chapter 2: Atoms, Molecules, and Ions
Atomic Masses
An atomic mass unit (amu) is defined as exactly one-twelfth the mass of a carbon-12 atom
1 u = × 10–24 g
The atomic mass of an element is the weighted average of the masses of the naturally occurring isotopes of that element
EOS
Chapter 2: Atoms, Molecules, and Ions

14. Chapter 2: Atoms, Molecules, and Ions
Periodic Table
Arranged the known elements in order of increasing atomic weight from left to right and from top to bottom in groups.
EOS
Elements that tend to most closely resemble each other are arranged in the same vertical group.
Chapter 2: Atoms, Molecules, and Ions

15. Chapter 2: Atoms, Molecules, and Ions
Modern Periodic Table
Elements are divided into two main classes
EOS
Chapter 2: Atoms, Molecules, and Ions

16. Chapter 2: Atoms, Molecules, and Ions
Modern Periodic Table
Except for hydrogen, those elements to the left of the line are metals
EOS
Chapter 2: Atoms, Molecules, and Ions

17. Chapter 2: Atoms, Molecules, and Ions
Modern Periodic Table
Elements to the right of the line are nonmetals
EOS
Chapter 2: Atoms, Molecules, and Ions

18. Chapter 2: Atoms, Molecules, and Ions
Modern Periodic Table
Elements around the line are referred to as metalloids
EOS
Chapter 2: Atoms, Molecules, and Ions

19. Introduction to Compounds
A molecule is a group of two or more atoms held together by covalent bonds.
A chemical formula is a symbolic representation of the composition of a compound in terms of its constituent elements.
EOS
Chapter 2: Atoms, Molecules, and Ions

20. Chapter 2: Atoms, Molecules, and Ions
Molecular Compounds
EOS
Ball-and-stick model vs. Space-filling model
Chapter 2: Atoms, Molecules, and Ions

21. Empirical and Molecular Formulas
Empirical formula: the simplest whole number ratio of elements in a compound
Example:
Molecular formula of glucose – C6H12O6
EOS
The elemental ratio C:H:O is 1:2:1, so the empirical formula is CH2O
EOS
Chapter 2: Atoms, Molecules, and Ions

22. Chapter 2: Atoms, Molecules, and Ions
Structural Formulas
Shows how atoms are attached to one another.
EOS
Chapter 2: Atoms, Molecules, and Ions

23. Chapter 2: Atoms, Molecules, and Ions

24. Chapter 2: Atoms, Molecules, and Ions

25. Chapter 2: Atoms, Molecules, and Ions

26. Binary Molecular Compounds
Compounds that are typically comprised of two nonmetallic elements:
e.g., CO, NO, HF
EOS
Molecular formulas are usually written with the more “metallic” first – “metallic” means farther left in the period and lower in the group
Chapter 2: Atoms, Molecules, and Ions

27. Binary Molecular Formulas
The lines trace a continuous path from boron (B) to fluorine (F). The element closer to the beginning of this path is generally written first in the formula of a binary molecular compound.
EOS
Chapter 2: Atoms, Molecules, and Ions

28. Formulas and Subscripts
Subscripts are used when a given atom is used more than once
e.g., H2O, CO2, N2O, HF, B2O3
The presence of subscripts is reflected in the names of compounds
EOS
Chapter 2: Atoms, Molecules, and Ions

29. Names of Binary Compounds
Consider the compounds CO and CO2
The compound name consists of two words, one for each element in the compound
Name the element that appears first in the formula: CARBON
The second element has an altered name: retain the stem of the element name and replace the ending by -ide
OXYGEN
 OXIDE
EOS
However, both compounds cannot be carbon oxide
Chapter 2: Atoms, Molecules, and Ions

30. Names of Binary Compounds
Consider the compounds CO and CO2
The names are further modified by adding prefixes to denote the numbers of atoms
EOS
Chapter 2: Atoms, Molecules, and Ions

31. Ions and Ionic Compounds
Atoms that gain or lose electrons are called ions
Positive ions: CATIONS Negative ions: ANIONS
Atoms that lose electrons form cations
Na  Na+ + e–
EOS
Atoms that gain electrons form anions
Cl + e–  Cl–
Chapter 2: Atoms, Molecules, and Ions

32. Chapter 2: Atoms, Molecules, and Ions
Monatomic Ions
Group A metals usually lose the number of electrons equal to their Group number.
Nonmetal atoms usually gain electrons and have a charge equal to their Group number minus eight.
The periodic table cannot be used to determine the charge on Group B metals.
EOS
For naming, Group B metals capable of multiple charges have the corresponding Roman numeral in parentheses added after the element name.
Chapter 2: Atoms, Molecules, and Ions

33. Chapter 2: Atoms, Molecules, and Ions
Common Monatomic Ions
EOS
Chapter 2: Atoms, Molecules, and Ions

34. Names and Formulas for Ionic Compounds
Ionic compounds form when oppositely charged ions are attracted to each other
NaCl
Resulting compound is electrically neutral
Na+ Cl–
(+1) + (–1) = 0
Ionic compound names use the cation name followed by the anion name
EOS
Sodium chloride
Chapter 2: Atoms, Molecules, and Ions

35. Chapter 2: Atoms, Molecules, and Ions
Polyatomic Ions
Polyatomic ions are charged groups of covalently bonded atoms
EOS
Chapter 2: Atoms, Molecules, and Ions

36. Chapter 2: Atoms, Molecules, and Ions
Hydrates
A hydrate is an ionic compound in which the formula unit includes a fixed number of water molecules associated with cations and anions
EOS
Examples:
BaCl2 . 2 H2O
CuSO4 . 5 H2O
Chapter 2: Atoms, Molecules, and Ions

37. Chapter 2: Atoms, Molecules, and Ions
Acids
Taste sour
Turn blue litmus paper red
React with metals to form hydrogen gas
Neutralize a base
IntroToAcids
EOS
Chapter 2: Atoms, Molecules, and Ions

38. Chapter 2: Atoms, Molecules, and Ions
Bases
Taste bitter
Turn red litmus paper blue
Feel slippery on skin
Neutralize an acid
IntroToBases
EOS
Chapter 2: Atoms, Molecules, and Ions

39. Chapter 2: Atoms, Molecules, and Ions
Arrhenius Concepts
Acids are compounds that ionize in water to form a solution of H+ ions and anions
Bases are compounds that ionize in water to form solutions of OH– and cations
Acids and bases react to form a salt and water
= neutralization
EOS
Chapter 2: Atoms, Molecules, and Ions

40. Chapter 2: Atoms, Molecules, and Ions
Arrhenius Concepts
Acids and bases react to form a salt and water
= neutralization
HCl + NaOH  “Salt” + Water
Acid Base Na
cation Cl
/anion
EOS
HOH
Chapter 2: Atoms, Molecules, and Ions

41. Formulas and Names for Acids
Binary acids start with hydro and end with “ic” plus the word acid
EOS
Ternary acids simply use the polyatomic anion name with “ate” changing to “ic” plus the word acid
Chapter 2: Atoms, Molecules, and Ions

42. Formulas and Names for Bases
Arrhenius bases always have hydroxide ions
The name follows ionic compound convention
e.g., NaOH – sodium hydroxide
EOS
Molecular bases form OH– after reacting with water
NH3 + HOH  NH4OH
Ammonia  ammonium hydroxide
Chapter 2: Atoms, Molecules, and Ions

43. Formulas and Names for Salts
Binary salts use the “ide” ending on the anion name
e.g., sodium chloride
Polyatomic salts use “ate” ending on the anion name
e.g., sodium sulfate
EOS
Chapter 2: Atoms, Molecules, and Ions

44. Electrolytic Dissociation and Conduction
Molten (liquid) ionic compounds and aqueous solutions of ionic compounds are good electrical conductors:
they form cations and anions in solution
EOS
Electrons can flow in these solutions, resulting in an electric current
Chapter 2: Atoms, Molecules, and Ions

45. Nonelectrolyte Solutions
Solutions of nonelectrolytes don’t conduct electricity since the solute is exclusively as molecules
Electrolytes and Nonelectrolytes
EOS
Chapter 2: Atoms, Molecules, and Ions

46. Strong/Weak Electrolytes
Strong electrolytes generate ions and are good conductors of electricity
Weak electrolytes partially ionize and are poor conductors of electricity
EOS
Chapter 2: Atoms, Molecules, and Ions

47. Ion Concentrations in Solutions
Brackets [ ] are used to represent molar concentrations in units of molarity, moles per liter, M
In a M solution of NaCl:
Since NaCl(s)  Na+(aq) + Cl–(aq)
in solution there is M Na+
and M Cl–
Dissolution Video
In a M solution of Na2SO4:
EOS
Na2SO4(s)  2 Na+(aq) + SO4–2(aq)
in solution there is M Na+ and M SO4–2
Chapter 2: Atoms, Molecules, and Ions

48. Chapter 2: Atoms, Molecules, and Ions
Strong and Weak Acids
Strong acids are acids that are completely ionized in water and are good conductors of electricity
Introduction to
Acids Clip
Weak acids are acids in which only some of the molecules are ionized in water; the rest remain as intact molecules
The dissociation of a weak acid in solution is written using a double arrow to indicate that the dissociation does not go to completion
EOS
Chapter 2: Atoms, Molecules, and Ions

49. Chapter 2: Atoms, Molecules, and Ions
Limited Ionization
Organic acids such as acetic acid are typical weak acids that have limited ionization in solution
CH3COOH(aq) CH3COO–(aq) + H+(aq)
EOS +
Chapter 2: Atoms, Molecules, and Ions

50. Recognizing Strong/Weak Acids
Molecular formulas of compounds with ionizable H atoms have the H atom written first – strong acids
e.g., HCl, H2SO4
EOS
Condensed structural formulas for weakly ionizable H atoms show the H at the end – weak acids
e.g., CH3COOH
Chapter 2: Atoms, Molecules, and Ions

51. Recognizing Strong/Weak Acids
Memorize the six strong acids
EOS
Chapter 2: Atoms, Molecules, and Ions

52. Chapter 2: Atoms, Molecules, and Ions
Strong and Weak Bases
Strong bases are ionic hydroxides that completely ionize in water - good conductors of electricity
Weak bases are substances that act as bases but remain mostly molecular at equilibrium in water
The dissociation of a weak base in solution is written using a double arrow to indicate that the dissociation does not go to completion
EOS
Ammonia, NH3, is a weak base
Chapter 2: Atoms, Molecules, and Ions

53. Recognizing Strong/Weak Bases
As with acids, memorize the few strong bases
EOS
Chapter 2: Atoms, Molecules, and Ions

54. Chapter 2: Atoms, Molecules, and Ions
Organic Compounds
Organic Chemistry is the study of carbon and its compounds
Carbon compounds containing one or more of the elements H, O, N, or S are especially common
Most organic compounds are molecular compounds
Can exist as acids, bases, and salts
Compounds have systematic names AND common names
EOS
Chapter 2: Atoms, Molecules, and Ions

55. Representations of Molecules
Structural Formula
Ball and Stick
EOS
Condensed Structural Formula CH3CH2CH3
Chapter 2: Atoms, Molecules, and Ions

56. Saturated Hydrocarbons
Hydrocarbons have only hydrogen and carbon atoms
Saturated hydrocarbon:
has the maximum number of hydrogen atoms possible for each carbon atom
EOS
Alkanes are saturated hydrocarbons
Methane (CH4) is the first molecule in the alkane series
Chapter 2: Atoms, Molecules, and Ions

57. Prefixes for Number of Carbon
Used for simple organic molecules
Combined with alkane ending “ane”
e.g., propane is a 3-carbon alkane
EOS
Chapter 2: Atoms, Molecules, and Ions

58. Chapter 2: Atoms, Molecules, and Ions
Table 20.2
Chapter 2: Atoms, Molecules, and Ions

59. Chapter 2: Atoms, Molecules, and Ions
Ethane Propane
Second most simple alkane
Minor ingredient of natural gas
Also known as bottled gas
Found in natural gas, but separately for commercial purposes
Chapter 2: Atoms, Molecules, and Ions

60. Chapter 2: Atoms, Molecules, and Ions
Butane
Gas used in Butane lighters
Four carbon chain allows for possible isomerizations
- Compounds which share
the same molecular
formula but differ in their
structural formula
Chapter 2: Atoms, Molecules, and Ions

61. Chapter 2: Atoms, Molecules, and Ions
Isomers
Compounds with the same molecular formula but different structural formulas
EOS
Chapter 2: Atoms, Molecules, and Ions

62. Chapter 2: Atoms, Molecules, and Ions
Cyclic Alkanes
Alkane compounds that have carbons arranged in a ring structure are called cycloalkanes.
use the prefix cyclo-
EOS
cyclohexane
methylcyclopropane
Chapter 2: Atoms, Molecules, and Ions

63. Chapter 2: Atoms, Molecules, and Ions
Ethene
Simplest member if the alkene family, also called ethylene
Most important commercial organic chemical
U.S. production over 20 billion kg, more than have is used in the production of polyethylene, one of the most familiar plastics.
Chapter 2: Atoms, Molecules, and Ions

64. Chapter 2: Atoms, Molecules, and Ions
Higher Level Alkenes
alkenes of containing four carbons provide the opportunity for isomerization, a change in the location of the double bond.
Different double bond positions result in different chemical properties
Chapter 2: Atoms, Molecules, and Ions

65. Chapter 2: Atoms, Molecules, and Ions
Ethyne
Commercially known as acetylene
Used as a fuel in welding torches
Past used a surgical anesthetic
Chapter 2: Atoms, Molecules, and Ions

66. Chapter 2: Atoms, Molecules, and Ions
Functional Groups
Specific groupings of atoms attached to a carbon chain that give the compound unique properties
Most-common functional groups include:
Alcohols
Ethers
Carboxylic Acids
Esters
Amines
EOS
Chapter 2: Atoms, Molecules, and Ions

67. Chapter 2: Atoms, Molecules, and Ions
Table 20.5
Chapter 2: Atoms, Molecules, and Ions

68. Chapter 2: Atoms, Molecules, and Ions
Alcohols
Alcohols are molecules that contain a hydroxyl group (OH)
EOS
Chapter 2: Atoms, Molecules, and Ions

69. Chapter 2: Atoms, Molecules, and Ions
Ethanol
Alcohol found in wine, liquor or beer
Industrial ethanol made from ethene is cheaper because it generally lacks the same taxes on the “recreational” alcohol
Although identical, industrial contains a noxious substance to prevent people from drinking it.
A solution of 70% ethanol by volume acts as an antiseptic by coagulating bacterial proteins
Chapter 2: Atoms, Molecules, and Ions

70. Chapter 2: Atoms, Molecules, and Ions
Iso-propanol
Commonly called rubbing alcohol
Used to give sponge baths to reduce high fevers.
Alcohol quickly evaporates removing heat from the skin surface, lowering one’s temperature
Chapter 2: Atoms, Molecules, and Ions

71. Chapter 2: Atoms, Molecules, and Ions
Propanetriol
Commonly known as glycerol, or glycerin
Very think, sweet tasting compound
Nontoxic, excellent carrier of medicine
Used by cosmetic industry in hand and skin creams because it acts as a good lubricant
Chapter 2: Atoms, Molecules, and Ions

72. STRUCTURE
Aldehyde
Ketone

73. EXAMPLES
2-Pentanone
4-Ethyl-3-hexanone

74. Example of Common Names
Methyl propyl ketone
Diethyl ketone

75. IUPAC Nomenclature of Aldehydes
Choose the longest continuous carbon chain that contains the carbonyl carbon
Number from the end of the chain closest to the carbonyl carbon (carbon #1!)
Aldehyde ending is -al
Do the aldehydes section of Organic Nomenclature
program.

76. EXAMPLES aldehyde group is always carbon 1 pentanal3 1 4 2
2-chloro-3-methylbutanal

77. SPECIAL CASES
formaldehyde
benzaldehyde
KNOW
THESE
acetaldehyde

78. Chapter 2: Atoms, Molecules, and Ions
Ethers
Ethers are molecules in which two alkane groups (R-) are attached to a central oxygen atom
The general formula is R-O-R´
EOS
CH3CH2OCH2CH3
CH3CH2OCH2CH2CH3
R and R´ may be the same or different groups
Chapter 2: Atoms, Molecules, and Ions

79. Chapter 2: Atoms, Molecules, and Ions
Carboxylic Acids
Carboxylic acids are alkanes that also contain a carboxyl group and are weak acids
Acts like an Arrhenius acid, loses a hydrogen ion
HCOO– + H+
EOS
Chapter 2: Atoms, Molecules, and Ions

80. Chapter 2: Atoms, Molecules, and Ions
Esters
Esters are molecules in which two alkanes are attached to each side of a carboxyl group
(R’-COO-R)
EOS
Chapter 2: Atoms, Molecules, and Ions

81. Chapter 2: Atoms, Molecules, and Ions
Amines
Amines are molecules in which alkanes and hydrogen(s) are attached to a central nitrogen
NH2(CH2)4NH2
EOS
Amines are weak bases
Chapter 2: Atoms, Molecules, and Ions

82. Chapter 2: Atoms, Molecules, and Ions
Summary of Concepts
The basic laws of chemical combination are the laws of conservation of mass, constant composition, and multiple proportions.
The three main subatomic particles are the protons, neutrons, and electrons.
Atoms with the same number of protons but different numbers of neutrons are called isotopes.
A chemical formula indicates the relative numbers of atoms of each type in a compound.
EOS
Chapter 2: Atoms, Molecules, and Ions

83. Chapter 2: Atoms, Molecules, and Ions
Summary (cont.)
The periodic table is an arrangement of the elements by atomic number that places elements with similar properties into the same vertical group.
Ions are formed by the gain or loss of electrons. Positive ions are cations and negative ions are anions.
Many compounds are classified as either acids (H+), bases (OH–), or salts (neutralization of acid and base).
Organic compounds are based on the element carbon.
Functional groups confer distinctive properties on an organic molecule.
EOS
Chapter 2: Atoms, Molecules, and Ions