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.
Laws of Chemical Composition
Conservation of Mass - The total mass
remains constant during a chemical
reaction.
Example: Decomposition
of mercuric oxide (HgO)
HgO(s) = Hg(l) + O2(g)
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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
Water always contains:
~89% oxygen
~11% hydrogen
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Basic Copper Carbonate
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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
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Law of Multiple Proportions
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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
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Atomic Theory Illustrated …
Note the laws of constant composition and
conservation of mass
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Subatomic Particles
Protons and neutrons are located at the center of
an atom called the nucleus.
Electrons are dispersed around the nucleus.
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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 Deuterium has 1 proton, 1 neutron Tritium has 1 proton, 2 neutrons -
Z=1
Z=1
Z=1
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Other Examples of Isotopes
Carbon-14
Z=6
so 8 neutrons
Chlorine-35
Z = 17
so 18 neutrons
Uranium-234
Z = 92
so 142 neutrons
The number of neutrons = A – Z
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Atomic Masses
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Atomic Masses
An atomic mass unit (amu) is defined as
exactly one-twelfth the mass of a carbon-12
atom
1 u = 1.66054 × 10–24 g
The atomic mass of an element is the
weighted average of the masses of the
naturally occurring isotopes of that element
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Periodic Table
Arranged the known elements in
order of increasing atomic weight
from left to right and from top to
bottom in groups.
Elements that tend to most
closely resemble each other are
arranged in the same vertical
group.
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Modern Periodic Table
Elements
are
divided
into two
main
classes
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Modern Periodic Table
Except for
hydrogen,
those
elements to
the left of the
line are
metals
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Modern Periodic Table
Elements to
the right of
the line are
nonmetals
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Modern Periodic Table
Elements
around the
line are
referred to as
metalloids
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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.
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Molecular Compounds
Ball-and-stick model vs. Spacefilling model
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Empirical and Molecular
Formulas
Empirical formula: the simplest whole number
ratio of elements in a compound
Example:
Molecular formula of glucose – C6H12O6
The elemental ratio C:H:O is 1:2:1, so the
empirical formula is CH2O
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Structural Formulas
Shows how atoms are attached to one another.
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Binary Molecular Compounds
Compounds that are typically comprised of two
nonmetallic elements:
e.g., CO, NO, HF
Molecular formulas are usually written with the
more “metallic” first – “metallic” means farther
left in the period and lower in the group
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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.
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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
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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
However, both compounds cannot be carbon oxide
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Names of Binary Compounds
Consider the compounds CO and CO2
The names are further modified by adding prefixes
to denote the numbers of atoms
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Ions and Ionic Compounds
Atoms that gain or lose electrons are called ions
Positive ions: CATIONS
Atoms that lose
electrons form cations
Na  Na+ + e–
Negative ions: ANIONS
Atoms that gain
electrons form anions
Cl + e–  Cl–
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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.
For naming, Group B metals capable of multiple
charges have the corresponding Roman numeral
in parentheses added after the element name.
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Common Monatomic Ions
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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
Sodium chloride
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Polyatomic Ions
Polyatomic
ions are
charged groups
of covalently
bonded atoms
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Hydrates
A hydrate is an ionic compound in which the
formula unit includes a fixed number of water
molecules associated with cations and anions
Examples:
BaCl2 . 2 H2O
CuSO4 . 5 H2O
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Acids
• Taste sour
• Turn blue litmus paper red
• React with metals to form
hydrogen gas
• Neutralize a base
IntroToAcids
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Bases
•
•
•
•
Taste bitter
Turn red litmus paper blue
Feel slippery on skin
Neutralize an acid
IntroToBases
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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
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Arrhenius Concepts
Acids and bases react to form a salt and water
= neutralization
HCl + NaOH  “Salt” + Water
Acid
Base
NaCl
HOH
cation/anion
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Formulas and Names for Acids
Binary acids start with
hydro and end with “ic”
plus the word acid
Ternary acids simply
use the polyatomic
anion name with “ate”
changing to “ic” plus
the word acid
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Formulas and Names for Bases
Arrhenius bases always have hydroxide ions
The name follows ionic compound convention
e.g., NaOH – sodium hydroxide
Molecular bases form OH– after reacting with
water
NH3 + HOH  NH4OH
Ammonia  ammonium hydroxide
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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
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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
Electrons can flow in these
solutions, resulting in an
electric current
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Nonelectrolyte Solutions
Solutions of nonelectrolytes
don’t conduct electricity since
the solute is exclusively as
molecules
Electrolytes and Nonelectrolytes
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Strong/Weak Electrolytes
Strong electrolytes
generate ions and are good
conductors of electricity
Weak electrolytes partially
ionize and are poor
conductors of electricity
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Ion Concentrations in Solutions
Brackets [ ] are used to represent molar concentrations
in units of molarity, moles per liter, M
In a 0.010 M solution of NaCl:
Since NaCl(s)  Na+(aq) + Cl–(aq)
in solution there is 0.010 M Na+
and 0.010 M Cl–
Dissolution Video
In a 0.010 M solution of Na2SO4:
Na2SO4(s)  2 Na+(aq) + SO4–2(aq)
in solution there is 0.020 M Na+ and 0.010 M SO4–2
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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
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Limited Ionization
Organic acids such as acetic acid are typical weak
acids that have limited ionization in solution
CH3COOH(aq)
CH3COO–(aq) + H+(aq)
+
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Recognizing Strong/Weak Acids
Molecular formulas of compounds with ionizable H
atoms have the H atom written first – strong acids
e.g., HCl, H2SO4
Condensed structural formulas for weakly ionizable
H atoms show the H at the end – weak acids
e.g., CH3COOH
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Recognizing Strong/Weak Acids
Memorize the six strong acids
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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
Ammonia, NH3, is a weak base
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Recognizing Strong/Weak Bases
As with acids, memorize the few strong bases
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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
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Representations of Molecules
Structural Formula
Ball and Stick
Condensed Structural Formula
CH3CH2CH3
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Saturated Hydrocarbons
Hydrocarbons have only hydrogen and carbon
atoms
Saturated hydrocarbon:
has the maximum number of
hydrogen atoms possible for
each carbon atom
Alkanes are saturated hydrocarbons
Methane (CH4) is the first molecule in
the alkane series
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Prefixes for Number of Carbon
Used for simple
organic molecules
Combined with
alkane ending
“ane”
e.g., propane is a
3-carbon alkane
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Table 20.2
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Ethane
Propane
• Second most simple
alkane
• Minor ingredient of
natural gas
H
H C
H
H
C
H
• Also known as bottled
gas
• Found in natural gas,
but separately for
commercial purposes
H
H
H C
H
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H
C
H
H
C
H
H
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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
H
H
H C C
H
H
H
H
H
C
H
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H
H
C
C H
H
H
H
C
C
H
H
H
C H
H
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Isomers
Compounds with the same molecular formula but
different structural formulas
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Cyclic Alkanes
Alkane compounds that have carbons arranged in a
ring structure are called cycloalkanes.
use the prefix cyclo-
methylcyclopropane
cyclohexane
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Ethene
• Simplest member if the
alkene family, also called
ethylene
H
• Most important
commercial organic
C
chemical
H
• U.S. production over 20
billion kg, more than have
is used in the production of
polyethylene, one of the
most familiar plastics.
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H
C
H
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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
H
C C
H
H
H
C
H
H
C H
H
H
H C C
H
H
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H
C
H
C H
H
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Ethyne
• Commercially
known as acetylene
• Used as a fuel in
welding torches
• Past used a surgical
anesthetic
H C C H
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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
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Table 20.5
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Alcohols
Alcohols are molecules that contain a hydroxyl
group (OH)
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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
H
H
H
C
H
C
H
OH
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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
H
H
C
H
OH
C
H
H
C
H
H
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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
HO
H
C
OH
C
OH
C
H
H
H
H
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STRUCTURE
Aldehyde
O
C
R
H
R = H, alkyl, aryl
Ketone
O
C
R
R'
R and R' = alkyl or aryl
R and R' cannot be hydrogen!
EXAMPLES
O
C
CH 3
CH 2
CH 2
CH 3
2-Pentanone
O
CH3
C
CH2
CH2
CH
CH3
CH2
CH3
4-Ethyl-3-hexanone
Example of Common Names
O
C
CH 3
CH 2
CH 2
CH 3
Methyl propyl ketone
O
CH3
C
CH2
CH3
CH2
Diethyl ketone
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.
EXAMPLES
H3C
CH2
CH2
CH2
C
aldehyde group is
always carbon 1
O
H
pentanal
Cl
4
CH3
3
CH
1
2
C
CH
CH3
O
H
2-chloro-3-methylbutanal
O
SPECIAL CASES
C
H
H
O
C H
formaldehyde
O
benzaldehyde
C
H
CH3
acetaldehyde
KNOW
THESE
Ethers
Ethers are molecules in which two alkane
groups (R-) are attached to a central oxygen
atom
The general formula is R-O-R´
R and R´ may be the same
or different groups
CH3CH2OCH2CH3
CH3CH2OCH2CH2CH3
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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+
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Esters
Esters are molecules in which two alkanes are
attached to each side of a carboxyl group
(R’-COO-R)
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Amines
Amines are molecules in which alkanes and
hydrogen(s) are attached to a central nitrogen
Amines are weak bases
NH2(CH2)4NH2
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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.
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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.
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