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Lecture Presentation
Chapter 2
Atoms, Molecules,
and Ions
John D. Bookstaver
St. Charles Community College
Cottleville, MO
© 2012 Pearson Education, Inc.
Atomic Theory of Matter
The theory that
atoms are the
fundamental
building blocks
of matter
reemerged in
the early
nineteenth
century,
championed by
John Dalton.
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Atoms,
Molecules,
and Ions
Dalton's Postulates
Each
element is
composed of
extremely
small
particles
called
atoms.
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Atoms,
Molecules,
and Ions
Dalton's Postulates
All atoms of a
given element are
identical to one
another in mass
and other
properties, but the
atoms of one
element are
different from the
atoms of all other
elements.
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Atoms,
Molecules,
and Ions
Dalton's Postulates
Atoms of an
element are not
changed into
atoms of a
different
element by
chemical
reactions;
atoms are
neither created
nor destroyed
in chemical
Atoms,
reactions. Molecules,
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and Ions
Dalton's Postulates
Compounds
are formed
when atoms
of more than
one element
combine; a
given
compound
always has
the same
relative
number and
kind of
atoms. Atoms,
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Molecules,
and Ions
Law of Conservation of Mass
The total mass of substances present at the
end of a chemical process is the same as the
mass of substances present before the
process took place.
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Atoms,
Molecules,
and Ions
The Electron
• Streams of negatively charged particles were found to
emanate from cathode tubes, causing fluorescence.
• J. J. Thomson is credited with their discovery (1897).
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Atoms,
Molecules,
and Ions
The Electron
Thomson measured the charge/mass ratio of
the electron to be 1.76  108 coulombs/gram
(C/g).
Atoms,
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Molecules,
and Ions
Millikan Oil-Drop Experiment
Once the
charge/mass
ratio of the
electron was
known,
determination of
either the
charge or the
mass of an
electron would
yield the other.
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Atoms,
Molecules,
and Ions
Millikan Oil-Drop Experiment
Robert Millikan
(University of
Chicago)
determined the
charge on the
electron in
1909.
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Atoms,
Molecules,
and Ions
Radioactivity
• Radioactivity is the spontaneous emission of
radiation by an atom.
• It was first observed by Henri Becquerel.
• Marie and Pierre Curie also studied it.
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Atoms,
Molecules,
and Ions
Radioactivity
• Three types of radiation were discovered by
Ernest Rutherford:
  particles
  particles
  rays
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Atoms,
Molecules,
and Ions
The Atom, circa 1900
• The prevailing theory
was that of the “plum
pudding” model, put
forward by Thomson.
• It featured a positive
sphere of matter with
negative electrons
imbedded in it.
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Atoms,
Molecules,
and Ions
Discovery of the Nucleus
Ernest
Rutherford shot
 particles at a
thin sheet of
gold foil and
observed the
pattern of scatter
of the particles.
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Atoms,
Molecules,
and Ions
The Nuclear Atom
Since some
particles were
deflected at
large angles,
Thomson’s
model could
not be correct.
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Atoms,
Molecules,
and Ions
The Nuclear Atom
• Rutherford
postulated a very
small, dense
nucleus with the
electrons around the
outside of the atom.
• Most of the volume
of the atom is empty
space.
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Atoms,
Molecules,
and Ions
Other Subatomic Particles
• Protons were discovered by Rutherford in
1919.
• Neutrons were discovered by James
Chadwick in 1932.
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Atoms,
Molecules,
and Ions
Subatomic Particles
• Protons and electrons are the only particles that
have a charge.
• Protons and neutrons have essentially the same
mass.
• The mass of an electron is so small we ignore it.
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Atoms,
Molecules,
and Ions
Symbols of Elements
Elements are symbolized by one or two
letters.
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Atoms,
Molecules,
and Ions
Symbols of Elements
All atoms of the same element have the same
number of protons, which is called the atomic
number, Z.
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Atoms,
Molecules,
and Ions
Symbols of Elements
The mass of an atom in atomic mass units
(amu) is the total number of protons and
neutrons in the atom.
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Atoms,
Molecules,
and Ions
Structure of the Nucleus
• Soddy discovered that the same element could
have atoms with different masses, which he
isotopes
called _______
there are 2 isotopes of chlorine found in nature, one
that has a mass of about 35 amu and another that
weighs about 37 amu
• The observed mass is a weighted average of the
weights of all the naturally occurring atoms
the atomic mass of chlorine is 35.45 amu
24
Isotopes
• Isotopes are atoms of the same element with
different masses.
• Isotopes have different numbers of neutrons.
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Atoms,
Molecules,
and Ions
Isotopes
• all isotopes of an element have the same number
of protons, but different number of neutrons
• isotopes of an element have different masses
numbers (A)
• isotopes are identified by their mass
_______________
protons + neutrons
26
Isotopes
• Cl-35 makes up about 75% of chlorine
atoms in nature, and Cl-37 makes up the
remaining 25%
• the average atomic mass of Cl is 35.45 amu
• Cl-35 has a mass number = 35, 17 protons
and 18 neutrons (35 - 17)
35
17
Cl
Atomic Symbol
A = mass number
Z = atomic number
AX
Z
27
Atomic Mass
Atomic and
molecular
masses can
be measured
with great
accuracy
using a mass
spectrometer.
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Atoms,
Molecules,
and Ions
Average Mass
• Because in the real world we use large
amounts of atoms and molecules, we use
average masses in calculations.
• Average mass is calculated from the
isotopes of an element weighted by their
relative abundances.
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Atoms,
Molecules,
and Ions
Periodic Table
• The periodic table is a systematic catalog of the
elements.
• Elements are arranged in order of atomic number.
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Atoms,
Molecules,
and Ions
Periodic Table
• The rows on the
periodic chart are
periods.
• Columns are
groups.
• Elements in the
same group have
similar chemical
properties.
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Atoms,
Molecules,
and Ions
The Modern Periodic Table
• Elements with similar chemical and physical
properties are in the same column
Families
Groups
• columns are called _______ or ________
– designated by a number and letter at top
Periods
• rows are called _______
• Main Group = ‘A’ groups
• Transition Elements = ‘B’ groups
– all metals
• Bottom rows = Inner Transition Elements
32
Atoms,
Molecules,
and Ions
Periodicity
When one looks at the chemical properties of
elements, one notices a repeating pattern of
reactivities.
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Atoms,
Molecules,
and Ions
Groups
These five groups are known by their names.
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Atoms,
Molecules,
and Ions
Important Groups – IA, Alkali Metals
• hydrogen usually
placed here, though it
doesn’t belong
• soft, low melting
points,low density
• flame tests  Li =
red, Na = yellow, K =
violet
• very reactive, never
find uncombined in
nature
35
lithium
sodium
potassium
rubidium
cesium
Atoms,
Molecules,
and Ions
Important Groups – IIA, Alkaline Earth
Metals
• harder, higher
melting, and denser
than alkali metals
beryllium
• flame tests  Ca =
red, Sr = red, Ba =
magnesium
yellow-green
calcium
• reactive, but less
strontium
than corresponding
barium
alkali metal
36
Atoms,
Molecules,
and Ions
Important Groups – VIIA, Halogens
• nonmetals
• F2 & Cl2 gases;
Br2 liquid; I2
solid
• all diatomic
• very reactive
fluorine
chlorine
bromine
iodine
37
Atoms,
Molecules,
and Ions
Important Groups – VIIIA, Noble
Gases
• all gases at room
temperature,
– very low melting and
boiling points
• very unreactive,
practically inert
• very hard to remove
electron from or give an
electron to
38
Atoms,
Molecules,
and Ions
Periodic Table
Nonmetals are on the right side of the periodic
table (with the exception of H).
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Atoms,
Molecules,
and Ions
Nonmetals
• poor conductors of heat
• poor conductors of
electricity
• solids are brittle
• gain electrons in reactions
to become anions
• upper right on the table
– except H
40
Atoms,
Molecules,
and Ions
Periodic Table
Metalloids border the stair-step line (with the
exception of Al, Po, and At).
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Atoms,
Molecules,
and Ions
Metalloids
• show some
properties of
metals and some
of nonmetals
• also known as
semiconductors
Properties of Silicon
shiny
conducts electricity
does not conduct heat well
brittle
42
Atoms,
Molecules,
and Ions
Periodic Table
Metals are on the left side of the chart.
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Atoms,
Molecules,
and Ions
Metals
• solids at room temperature, except Hg
• reflective surface
– shiny
• conduct heat
• conduct electricity
• malleable
– can be shaped
• ductile
– drawn or pulled into wires
• lose electrons and form cations in
reactions
• about 75% of the elements are metals
• lower left on the table
44
Atoms,
Molecules,
and Ions
Atomic Structures of Ions
• Metals form cations
• For each positive charge the ion has 1 less electron than
the neutral atom
 Na atom = 11 p+ and 11 e-, Na+ ion = 11 p+ and 10 e Ca atom = 20 p+ and 20 e-, Ca2+ ion = 20 p+ and 18 e-
• Cations are named the same as the metal
sodium
Na  Na+ + 1esodium ion
calcium
Ca  Ca2+ + 2ecalcium ion
• The charge on a cation can be determined from the
Group number on the Periodic Table
 Group 1A  1+, Group 2A  2+, (Al, Ga, In)  3+
45
Atomic Structures of Ions
• Nonmetals form anions
• For each negative charge the ion has 1 more electron
than the neutral atom
 F = 9 e-, F- = 10 e P = 15 e-, P3- = 18 e-
• Anions are named by changing the ending of the name
to -ide
fluorine
F + 1e-  Ffluoride ion
oxygen
O + 2e-  O2oxide ion
• The charge on an anion can be determined from the
Group number on the Periodic Table
 Group 7A  1–, Group 6A  2–
46
Atomic Structures of Ions
+
-
Ion
p
e
Cl–
17
19
18
18
2–
16
18
2+
38
36
K+
S
Sr
47
Classifying Materials
• atomic elements = elements whose
particles are single atoms (i.e. Cu)
• molecular elements = elements whose
particles are multi-atom molecules
(i.e. O2)
• 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)
48
Molecular Elements
• 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
VIIA
H2
N2
7
O2
F2
Cl2
Br2
I2
49
Ionic Compounds
cation + _________
anion
• _______
• no individual
molecule units, instead
have a 3-dimensional
array of cations and
anions made of
formula units
50
Molecular View of
Elements and Compounds
51
Nomenclature
Common Names - Exceptions
•
•
•
•
•
water
H2O = _______
ammonia
NH3 = ___________
CH4 = methane
__________
salt
NaCl = table
__________
sugar
C12H22O11 = table
____________
52
Chemical Formulas
The subscript to the right
of the symbol of an
element tells the number
of atoms of that element
in one molecule of the
compound.
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Atoms,
Molecules,
and Ions
Chemical Formulas
Molecular compounds
are composed of
molecules and almost
always contain only
nonmetals.
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Atoms,
Molecules,
and Ions
Diatomic Molecules
• These seven elements occur naturally
as molecules containing two atoms:
– Hydrogen
– Nitrogen
– Oxygen
– Fluorine
– Chlorine
– Bromine
– Iodine
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Atoms,
Molecules,
and Ions
Types of Formulas
• Empirical formulas give the lowest wholenumber ratio of atoms of each element in a
compound.
• Molecular formulas give the exact number
of atoms of each element in a compound.
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Atoms,
Molecules,
and Ions
Types of Formulas
• Structural formulas show
the order in which atoms are
bonded.
• Perspective drawings also
show the three-dimensional
array of atoms in a
compound.
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Atoms,
Molecules,
and Ions
Ions
• When atoms lose or gain electrons, they
become ions.
– Cations are positive and are formed by elements
on the left side of the periodic chart.
– Anions are negative and are formed by elements
on the right side of the periodic chart.
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Atoms,
Molecules,
and Ions
Ionic Bonds
Ionic compounds (such as NaCl) are
generally formed between metals and
nonmetals.
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Atoms,
Molecules,
and Ions
Writing Formulas
• Because compounds are electrically neutral,
one can determine the formula of a
compound this way:
– The charge on the cation becomes the subscript
on the anion.
– The charge on the anion becomes the subscript
on the cation.
– If these subscripts are not in the lowest wholenumber ratio, divide them by the greatest common
Atoms,
factor.
Molecules,
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and Ions
Common Cations
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Atoms,
Molecules,
and Ions
Common Anions
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Atoms,
Molecules,
and Ions
• Ionic
Nomenclature
Major Classes
 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
63
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
 mostly transition metals
64
Type I Binary Ionic Compounds
• Contain Metal Cation + Nonmetal Anion
• Metal listed first in formula & name
1. name metal cation first, name nonmetal anion
second
2. cation name is the metal name
3. nonmetal anion named by changing the ending
on the nonmetal name to -ide
65
Type II Binary Ionic Compounds
•
•
Contain Metal Cation + Nonmetal Anion
Metal listed first in formula & name
1. name metal cation first, name nonmetal anion second
2. metal cation name is the metal name followed by a
Roman Numeral in parentheses to indicate its charge
3. nonmetal anion named by changing the ending on the
nonmetal name to -ide
66
Examples
•
•
•
•
•
•
•
lithium chloride
LiCl = _________________
chloride
AlCl3 = aluminum
____________________
oxide
PbO = lead(II)
______________
oxide
PbO2 = lead(IV)
_______________
manganese(III) oxide
Mn2O3 = _______________________
zinc chloride
ZnCl2 = ______________
chloride
AgCl = silver
_______________
67
Example – Name the following
compounds:
Na2SO4  sodium sulfate
Fe(NO3)3  iron(III) nitrate
68
Binary Molecular Compounds
of 2 Nonmetals
1. Name first element in formula first
 use the full name of the element
2. Name the second element in the formula with an -ide
 as if it were an anion, however, remember these
compounds do not contain ions!
3. Use a prefix in front of each name to indicate the
number of atoms
a) Do not use the prefix mono- on the first element
69
Subscript - Prefixes
mono• 1 = ________;
 not used on first nonmetal
•
•
•
•
•
•
•
•
•
•
2 = di_______
3 = tri_______
4 = tetra_______ Example – Name the
5 = penta_______ following compound:
6 = hexa_______
boron
trifluoride
BF

3
7 = hepta_______
8 = octa_______
9 = nona_______
10 = deca_______
70
drop last “a or o” if name begins with vowel
Acids
• Contain H+ cation in
aqueous solution
• Binary acids have H+
cation and nonmetal
anion
• Oxyacids have H+
cation and
polyatomic anion
containing oxygen
71
Acids
• acids are molecular compounds that often behave like they
are made of ions
• All names have acid at end
• Binary Acids = hydro prefix + stem of the name of the
nonmetal + ic suffix
72
• Oxyacids
Acids
 if polyatomic ion ends in –ate = name of polyatomic ion with –ic
suffix
 if polyatomic ion ends in –ite = name of polyatomic ion with –ous
suffix
73
Example – Name the following
compounds:
HCl 
hydrochloric acid
H2SO4 
sulfuric acid
H2SO3 
sulfurous acid
74
Inorganic Nomenclature
• Write the name of the cation.
• If the anion is an element, change its
ending to -ide; if the anion is a polyatomic
ion, simply write the name of the
polyatomic ion.
• If the cation can have more than one
possible charge, write the charge as a
Roman numeral in parentheses.
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Atoms,
Molecules,
and Ions
Patterns in Oxyanion Nomenclature
• When there are two oxyanions involving the
same element:
– The one with fewer oxygens ends in -ite.
– The one with more oxygens ends in -ate.
• NO2− : nitrite; SO32− : sulfite
• NO3− : nitrate; SO42− : sulfate
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Atoms,
Molecules,
and Ions
Patterns in Oxyanion Nomenclature
• Central atoms on the second row have bond
to at most three oxygens; those on the third
row take up to four.
• Charges increase as you go from right to left.
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Atoms,
Molecules,
and Ions
Patterns in Oxyanion Nomenclature
• The one with the second fewest oxygens ends in -ite.
– ClO2− : chlorite
• The one with the second most oxygens ends in -ate.
– ClO3− : chlorate
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Atoms,
Molecules,
and Ions
Patterns in Oxyanion Nomenclature
• The one with the fewest oxygens has the prefix
hypo- and ends in -ite.
– ClO− : hypochlorite
• The one with the most oxygens has the prefix
per- and ends in -ate.
– ClO4− : perchlorate
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Atoms,
Molecules,
and Ions
Acid Nomenclature
• If the anion in the acid
ends in -ide, change
the ending to -ic acid
and add the prefix
hydro- .
– HCl: hydrochloric acid
– HBr: hydrobromic acid
– HI: hydroiodic acid
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Atoms,
Molecules,
and Ions
Acid Nomenclature
• If the anion in the acid
ends in -ite, change the
ending to -ous acid.
– HClO: hypochlorous acid
– HClO2: chlorous acid
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Atoms,
Molecules,
and Ions
Acid Nomenclature
• If the anion in the acid
ends in -ate, change
the ending to -ic acid.
– HClO3: chloric acid
– HClO4: perchloric acid
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Atoms,
Molecules,
and Ions
Nomenclature of Binary Compounds
• The less electronegative
atom is usually listed first.
• A prefix is used to denote
the number of atoms of
each element in the
compound (mono- is not
used on the first element
listed, however) .
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Atoms,
Molecules,
and Ions
Nomenclature of Binary Compounds
• The ending on the more
electronegative element
is changed to -ide.
– CO2: carbon dioxide
– CCl4: carbon tetrachloride
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Atoms,
Molecules,
and Ions
Nomenclature of Binary Compounds
• If the prefix ends with a
or o and the name of the
element begins with a
vowel, the two
successive vowels are
often elided into one.
N2O5: dinitrogen pentoxide
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Atoms,
Molecules,
and Ions
Nomenclature of Organic Compounds
• Organic chemistry is the study of carbon.
• Organic chemistry has its own system of
nomenclature.
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Atoms,
Molecules,
and Ions
Nomenclature of Organic Compounds
The simplest hydrocarbons (compounds
containing only carbon and hydrogen) are
alkanes.
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Atoms,
Molecules,
and Ions
Nomenclature of Organic Compounds
The first part of the names just listed
correspond to the number of carbons
(meth- = 1, eth- = 2, prop- = 3, etc.).
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Atoms,
Molecules,
and Ions
Nomenclature of Organic Compounds
• When a hydrogen in an alkane is replaced with
something else (a functional group, like -OH in
the compounds above), the name is derived from
the name of the alkane.
• The ending denotes the type of compound.
– An alcohol ends in -ol.
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Atoms,
Molecules,
and Ions