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Chemistry, The Central Science, 11th edition
Theodore L. Brown; H. Eugene LeMay, Jr.;
and Bruce E. Bursten
Chapter 2
Atoms, Molecules,
and Ions
http://www.youtube.com/watch?v=vUzTQWn-wfE&feature=related
Mrs. Deborah Amuso
Camden High School
Camden, NY 13440
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Atomic Theory
The earliest philosophers questioned: Can matter be
subdivided into fundamental particles?
Democritus (460-380 B.C.) – He coined the word ‘atomos’
– he said matter is made of tiny hard indivisible
particles.
Recall from Chapter 1: Atoms are the building blocks
of matter. An atom is the smallest representative
particle of an element.
Atoms,
Molecules,
and Ions
John Dalton
John Dalton (1808) is famous for his Atomic
Theory because his 4 key postulates helped
to explain the known Laws of the time &
actually predicted the Law of Multiple
Proportions.
Atoms,
Molecules,
and Ions
Dalton's 4 Postulates
1. Elements are composed of atoms.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Dalton's 4 Postulates
2. All atoms of a given element are identical .
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Dalton's 4 Postulates
3. In chemical reactions atoms are not
changed into different types of atoms.
Atoms are neither created nor destroyed.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Dalton’s 4 Postulates
4. Compounds are formed when atoms of
elements combine.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Law of Constant Composition
Joseph Proust (1754–1826)
• This is also known as the Law of
Definite Proportions.
• It states that the elemental composition
of a pure substance never varies.
• In a given compound, the relative
numbers and kinds of atoms are always
the same, regardless of its source.
• Vitamin C is always C3H4O3
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Law of Conservation of Mass
• Matter cannot be created or destroyed during
ordinary chemical reactions, the atoms simply
rearrange to form new substances.
• Total mass before Rx = Total mass after Rx
• 5 grams A + 7 grams B = 12 grams AB
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Law of Multiple Proportions
• When elements A and B are able to form
more than one compound: The masses of B
than can combine with a given mass of A are
in small whole number ratios.
• For example: CO (carbon monoxide) & CO2 (carbon dioxide)
• Here’s the proof using sulfur-fluorine compounds as
an example:
Compound 1: 23.2 g S & 55.0 g F
Compound 2: 16.6 g S & 9.8 g F
Compound 3: 19.3 g S & 68.6 g F
Atoms,
Molecules,
and Ions
To Prove the Law
• Step 1: Find the F/S ratio
Compound 1: 55.0/23.2 = 2.37
Compound 2: 9.8/16.6 = 0.59
Compound 3: 68.6/19.3 = 3.55
• Step 2: Find simplest ratio
Compound 1: 2.37/0.59 = 4
Compound 2: 0.59/0.59 = 1
Compound 3: 3.55/0.59 = 6
• Surprised? The compounds are
SF4, SF, and SF6
Atoms,
Molecules,
and Ions
J. J. Thompson
J. J. Thompson (1897)
He used Cathode Ray Tubes to measure the charge/mass
ratio for an electron.
He is credited with discovery of the electron.
This lead to the Plum-Pudding Model of the atom.
http://www.youtube.com/watch?v=YG-Wz-arcaY&feature=related
Atoms,
Molecules,
and Ions
The Electron
• Streams of negatively charged particles were
found to emanate from cathode tubes.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Plum Pudding Model of the Atom
circa 1900
• The prevailing theory
was that of the “Plum
Pudding” Model, put
forward by Thompson.
• It featured a positive
sphere of matter with
negative electrons
imbedded in it.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Robert Millikan
Robert Millikan (1909) – He determined the
charge on an electron during his famous
Oil Drop Experiment.
http://www.youtube.com/watch?v=XMfYHag7Liw
Atoms,
Molecules,
and Ions
Millikan Oil Drop Experiment
Charge on the electron is
1.602 x 10-19
Coulombs
Atoms,
Molecules,
and Ions
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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.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Radioactivity
Three types of radiation were discovered by Ernest
Rutherford:
 particles (positively charged) = Alpha
 particles (negatively charged) = Beta
 rays (not a particle – no charge) = Gamma
http://www.youtube.com/watch?v=vuGvQjCOdr0&feature=related
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Ernest Rutherford
Ernest Rutherford (1911) – His Gold Foil Alpha
Scattering Experiment led to the discovery of
protons and the nucleus – He showed that
atoms have a positive center and are mostly
empty space.
http://www.youtube.com/watch?v=5pZj0u_XMbc
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.
Atoms,
Molecules,
and Ions
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The Nuclear Atom
Since some particles
were deflected at
large angles,
Thompson’s model
could not be correct.
Atoms,
Molecules,
and Ions
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Nuclear Model of the 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.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Bohr Model of the Atom
Niels Bohr (1913) – His work studying light
given off by excited atoms led to the
proposal that electrons move around the
nucleus in specific electron shells.
http://www.youtube.com/watch?v=wCCz20JOXXk
Atoms,
Molecules,
and Ions
James Chadwick
James Chadwick (1932) – He discovered
neutrons
Atoms,
Molecules,
and Ions
Most Modern Model of the Atom
The Modern Model – also called Electron Cloud
Model or Orbital Model or Wave Mechanical
Model – This model says it is impossible to
know exactly where an electron is at any given
time. Electrons are in regions of space called
orbitals.
You will learn more about this
model & the scientists that
contributed to the development
of this model in Chapter 6.
Atoms,
Molecules,
and Ions
The Periodic Table
1. Arranges the elements by increasing
ATOMIC NUMBER (not mass).
2. GROUPS (vertical columns) contain
atoms having the same # of valence
electrons & similar chemical properties.
3. PERIODS (horizontal rows) contain
atoms having the same # of occupied
electron shells. Their properties vary
from metal to metalloid to nonmetal.
Atoms,
Molecules,
and Ions
Periodicity
When one looks at the chemical properties of
elements, one notices a repeating pattern of
reactivities.
Atoms,
Molecules,
and Ions
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Group Names to Know
Group 1 = Alkali Metals
Group 2 = Alkaline Earth Metals
Groups 3 to 12 = Transition Metals
Group 16 = Chalcogens
Group 17 = Halogens
Group 18 = Noble Gases
Atoms,
Molecules,
and Ions
Classes of Elements
1. METALS – have luster, malleable,
ductile, conductors of heat & electricity.
2. METALLOIDS – have properties of
both metals & nonmetals.
3. NONMETALS – if solid, they are brittle
& poor conductors.
4. NOBLE GASES – inert (don’t react)
Atoms,
gases
Molecules,
and Ions
Location
• METALS – left of staircase
(except hydrogen which is a nonmetal)
• NONMETALS – right of staircase and hydrogen
• METALLOIDS – on staircase (B, Si, Ge, As, Sb, Te)
• NOBLE GASES – in Group 18 (often considered
nonmetals)
Atoms,
Molecules,
and Ions
Periodic Table
Nonmetals are
on the right
side of the
periodic table
(with the
exception of H).
Notice that some
textbooks consider
the noble gases to
also be nonmetals.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Periodic Table
Metalloids
border the
stair-step line
(with the
exception of
Al, Po, and
At).
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Periodic Table
Metals are
on the left
side of the
chart.
(except H)
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Subatomic Particles
1. Proton – Positive Charge, Mass = about 1 amu
2. Neutron – Neutral, Mass = about 1 amu
3. Electron – Negative Charge, Mass = 1/1836 amu
Atoms,
Molecules,
and Ions
Atoms: Bohr Model
Summary
1. While most of the volume of the atom is empty space,
atoms do have a central dense positive nucleus
(containing positive protons & neutral neutrons).
2. Negative electrons circle the nucleus in specific energy
levels.
3. Each atom is NEUTRAL because its # of protons
equals its # of electrons.
4. All atoms of a given element have the same ATOMIC
NUMBER (same # of protons).
Atoms,
5. The MASS NUMBER is the sum of the
Molecules,
# of protons + # of neutrons in an atom.
and Ions
Symbols of Elements
Elements are symbolized by one or two
letters.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Atomic Number
All atoms of the same element have the same
number of protons:
The atomic number (Z)
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Atomic Mass
The mass of an atom in atomic mass units
(amu) is the total number of protons and
neutrons in the atom.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Atomic Mass
Atomic and
molecular masses
can be measured
with great accuracy
with a mass
spectrometer.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Isotopes
1. ISOTOPES are atoms of the same element
with different masses due to differences in
# of neutrons.
2. Notation:
3
1H
3 = mass number
1 = atomic number
3. Another way: H-3
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.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Atomic Mass
1. The mass of an atom is measured in a
unit called the amu.
2. One ATOMIC MASS UNIT (amu) =
1/12 the mass of a carbon-12 atom or
1.66 x 10-24g.
3. The ATOMIC MASS or AVERAGE
ATOMIC MASS of an element is
calculated from the relative
abundances and atomic masses of that
element’s isotopes.
Atoms,
Molecules,
and Ions
Calculating Avg. Atomic Mass
(also called atomic weight – AW)
There are 3 steps:
1) For each isotope, multiply its atomic
mass times it percent abundance.
2) Add each of these values together.
3) Divide by 100 to obtain the avg atomic
mass if you didn’t use the % sign.
AW = [(atomic mass)(%)] + [(atomic mass)(%)]
Then, ask yourself if your answer for the average makes sense?
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Example
Rubidium has 2 naturally occurring isotopes. Rb-85
(atomic mass = 84.9118 amu, abundance 72.15%)
and Rb-87 (atomic mass = 86.9092 amu, abundance
27.85%)
1. Calculate its atomic weight using:
AW = [(atomic mass)(%)] + [(atomic mass)(%)]
2. Set-up:
AW = [(84.9118)(72.15%)] + [(86.9092)(27.85%)
3. Answer: AW = (61.26) + (24.20) = 85.46 amu*
*If you got 8546 amu for the answer, you need to divide by 100
Atoms,
Molecules,
and Ions
Calculating P, E, N for Neutral Atoms
# Protons = Atomic Number (42)
# Electrons = Atomic Number (42)
Mass number = Atomic Mass rounded-off to nearest whole number (96)
# Neutrons = Mass Number – Atomic Number (96 – 42 = 54)
Atoms,
Molecules,
and Ions
Chemical Formulas
1. 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.
2. There are 2 basic types of
compounds: Molecular or Ionic.
3. There are 3 types of chemical
formulas: molecular, empirical, &
structural.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Types of Compounds: Molecular or Ionic
Molecular compounds are
composed of molecules
and almost always
contain only nonmetals.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Types of Compounds: Molecular or Ionic
Diatomic Molecules: These seven elements
occur naturally as molecules containing two
atoms.
Remember: HOFBrINCl
While these are elements and not compounds, they should be
mentioned at this time because they are also examples of
molecules.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Types of Compounds: Molecular or Ionic
Ionic compounds (such as NaCl) are
generally formed between metals and
nonmetals and/or polyatomic ions.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Types of Formulas:
Empirical, Molecular, or Structural
• Empirical formulas give the lowest
whole-number ratio of atoms of each
element in a compound.
• Molecular formulas give the exact
number of atoms of each element in
one molecule of a compound.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Examples
• Molecular Formulas for Molecular
Compounds
CO2 , NH3
CH4 , HCl
• Empirical Formula for
an Ionic Compound
NaCl
Atoms,
Molecules,
and Ions
Types of Formulas:
Empirical, Molecular, or Structural
• Structural formulas
show the order in which
atoms are bonded.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Ions
• Ions are atoms that have lost or gained their
electrons and as a result are no longer
neutral in charge.
• The resulting ion has an octet (8 valence
electrons).
• Metals lose electrons & form positive ions.
• Nonmetals gain electrons & form negative
ions.
Atoms,
Molecules,
and Ions
Ions – Memorize these!
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.
These ions are formed from a single atom and are called
Monoatomic ions.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Ions with Multiple Charges
• Usually transition metals
• Two Examples: Memorize these two!
Cuprous (Cu 1+) vs Cupric (Cu 2+)
Ferrous (Fe 2+) vs Ferric (Fe 3+)
• Pattern:
Lois Lane is superman’s girlfriend.
The lower charge is the –ous ion.
Get it? Low-ous (Lois)
Atoms,
Molecules,
and Ions
Polyatomic Ions
1. Polyatomic Ion - A group of covalently
bonded atoms that have lost or gained
electron(s) and as a result have an
electronic charge.
2. Example:
SO4 2- = Sulfate Ion
Atoms,
Molecules,
and Ions
Common Anions - Memorize
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Common Cations - Memorize
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Finding # P, E, N for ions
Recall - For Neutral Atoms:
# p = atomic number
# e = atomic number
# n = mass number – atomic number
Ions are atoms that have lost or gained
electrons. While the # p and # n in the atom
and its corresponding ion are the same,
Atoms,
the # e differs.
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Finding # P, E, N for ions
Positive cations are formed from atoms that
have LOST electrons.
23
11Na atom
vs
23
1+ ion
Na
11
Atom: 11 Protons, 12 Neutrons, 11 Electrons
The +1 charge on the ion means it has one less electron.
Ion: 11 Proton, 12 Neutron, 10 Electrons
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Finding # P, E, N for ions
Negative anions are formed from atoms that
have GAINED electrons.
35
17Cl atom
vs
35
1- ion
Cl
17
Atom: 17 Protons, 18 Neutrons, 17 Electrons
The -1 charge on the ion means it has 1 extra electron.
Ion: 17 Proton, 18 Neutron, 18 Electrons
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Review: Formulas for Compounds
• Molecular formulas tell the exact # and
kind of atom in one molecule of the
compound. Molecular compounds
contain only nonmetallic elements.
Examples: H2O or C6H12O6
• Empirical formulas tell the simplest whole
number ratio between the atoms in the
compound. Ionic compounds contain
Atoms,
metals and nonmetals and/or polyatomicMolecules,
and Ions
ions. Examples: NaCl or NH4Br
Writing Formulas
• Because compounds are electrically neutral,
one can determine the formula of a
compound by criss-crossing ion charges.
– 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,
and Ions
© 2009, Prentice-Hall, Inc.
Steps to Writing Formulas
1.
2.
3.
4.
List symbol and charge of cation.
List symbol and charge of anion.
If either is polyatomic put ( ) around it.
If there is a Roman numeral in the name, it tells the
charge on the cation.
5. Criss-cross charges.
6. Simplify.
Example #1: Barium Phosphate
Ba2+ (PO4)3-

Ba3(PO4)2
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Writing Formulas
Example #2: Calcium Sulfide
Ca2+ S2- 
Ca2S2  simplify  CaS
Example #3: Magnesium Hydroxide
Mg2+ (OH)1- 
Mg(OH)2
Use must keep ( )
Example #4: Iron (III) Oxide – also named ferric oxide
Fe3+ O2- 
Fe2O3
Example #5: Copper (II) Sulfate – also named cupric sulfate
Cu2+ (SO4 )2- 
Cu2(SO4 )2  simplify  CuSO4
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Steps to Nomenclature (Naming)
1. Write the name of the cation.
2. 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.
3. If the cation can have more than one possible
charge, write the charge as a Roman numeral in
parentheses.
Example #1: (NH4)2CO3 
Ammonium Carbonate
Example #2: AgBr 
Silver Bromide
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Nomenclature (Naming)
Example #3: NaC2H3O2 
Sodium Acetate
Example #4: FeCl2 
Iron (II) Chloride or Ferrous Chloride
Example #5: Sr(NO3)2 
Strontium Nitrate
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Oxyanion Patterns
1. Oxyanions = Negative ions that contain
oxygen
2. Knowing this naming pattern can help you
memorize the ion names more easily.
2. Look at the pattern using chlorine w/ oxygen.
Chloride ion = Cl 1Hypochlorite ion = ClO 1Chlorite ion = ClO2 1Chlorate ion = ClO3 1Atoms,
Molecules,
Perchlorate ion = ClO4 1and Ions
Some Common Oxyanions
Nitrite = NO2 1-
Nitrate = NO3
1-
one more oxygen
Sulfite = SO3 2-
Sulfate = SO4 2-
Note: The –ite ion doesn’t always have 2 oxygen
atoms. However the -ate ion always has 1 more
oxygen atom than the –ite ion!
Atoms,
Molecules,
and Ions
You try:
1. If bromate ion = BrO3 1-, then bromite = ?
ans. BrO2 12. If carbonate = CO3 2- and hydrogen = H 1+, then
what is the hydrogen carbonate ion?
ans. HCO3 1Another name for hydrogen carbonate is
bicarbonate.
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
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Acid Nomenclature
• If the anion in the acid
ends in -ite, change
the ending to -ous
acid.
– HClO: hypochlorous
acid
– HClO2: chlorous acid
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Acid Nomenclature
• If the anion in the acid
ends in -ate, change
the ending to -ic acid.
– HClO3: chloric acid
– HClO4: perchloric acid
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Steps: Nomenclature of Binary Molecules
1. Binary Molecules contain just 2 different nonmetals.
2. The less electronegative atom is usually listed first.
3. 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).
4. The ending on the more electronegative element is changed
to –ide.
CO2 
carbon dioxide
CCl4 
carbon tetrachloride
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Nomenclature of Binary Molecules
Note: If the prefix ends with a or o and
the name of the element begins with
Memorize these prefixes!
a vowel, the two successive vowels
are often elided into one.
N2O5 
dinitrogen pentoxide
SO3 
sulfur trioxide*
*Don’t confuse this with the polyatomic ion SO3 2as SO3 is a neutral molecule.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Nomenclature
• Also be able to name or given formulas
for these compounds:
Water = H2O
Methane = CH4
Ammonia = NH3
Hydrogen Peroxide = H2O2
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.