SECTION 3.1
Atomic Structure
ATOMS AND THE PERIODIC TABLE
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Chapter Preview
 3.1 Atomic Structure
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3.2 A Guided Tour of The Periodic Table
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Organization of the Periodic Table
Some atoms form Ions
How Do the Structures of Atoms Differ?
3.3 Families of Elements
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What are Atoms?
What’s in an Atom?
Models of the Atoms
How Are Elements Classified?
 Metals
 Nonmetals
3.4 Using Moles to Count Atoms
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Counting Things
Calculating with Moles
UNDERSTANDING OF ATOMS
In the fourth century B.C., Democritus, a Greek
philosopher, suggested that the universe was
made of invisible units called atoms.
 Atom meaning “unable to be divided”
 However, Democritus theory of atoms was
unconvincing to other scientists, which led to
more research.
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DALTON’S ATOMIC THEORY
In 1808, an English teacher, John Dalton, proposed
his own theory:
 Every element is made of tiny, unique particles
called atoms that cannot be subdivided
 Atoms of the same element are exactly alike.
 Atoms of different elements can join to form
molecules. Ex. H2O
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WHAT’S IN THE ATOM?
At the center of the atom there is a nucleus made
of protons and neutrons.
 On the outside of the nucleus are where the
electrons are located.
 Protons have a positive charge
 Electrons have a negative charge
 Neutrons are neutral
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MODEL OF THE ATOM
In 1913, the Danish scientist, Niels Bohr,
suggested that electrons in an atom move in set
paths around the nucleus much like planets orbit
the sun.
 Each electron has a certain path known as the
energy level.
 However, the modern model determined that
electrons did not orbit the nucleus in set paths
but behaved more like waves on a vibrating
string
 It is impossible to determine both the exact
location of an electron and its speed and direction
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ORBITALS
Electrons are found in a region called an orbital
 There are 4 different types of orbitals:
 S orbital which is the simplest and more likely to
surround the nucleus
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Z
Y
X
ORBITALS
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The second is the P orbitals, which are dumbell
shaped and can be 3 different ways in space.
Z
Y
Z
Z
Y
X
X
Y
X
ORBITALS
The last are the d orbitals, which occur 5 ways in
space and the f orbitals, which occur 7 ways in
space.
 Each orbital can only hold 2 electrons
 Electrons will occupy the lowest energy levels
first, which mean they occupy orbitals with the
lowest energy.
 Orbitals are occupied in this order: s – p – d – f
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VALENCE ELECTRONS
Every atom has 1 or more valence electrons
 Valence electrons are in the outermost energy
level of an atom.
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SECTION 3.1 SUMMARY
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Elements are made of very small units called atoms.
The nucleus of an atom is made of positively charged
protons and uncharged neutrons.
Surrounding the nucleus are tiny negatively charged
electrons.
Atoms have an equal number of protons and electrons.
In Bohr’s model of the atom, electrons orbit the nucleus in
set paths much like the planets orbit the sun in our solar
system.
In the modern atomic model, electrons are found in orbitals
within each energy level.
Electrons in the outermost energy level are called valence
electrons.
SECTION 3.2
A GUIDED TOUR OF THE PERIODIC TABLE
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Section 3.2 Objective
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Relate the organization of the periodic table to the
arrangement of electrons within an atom.
Explain why some atoms gain or lose electrons to form ions.
Determine how many protons, neutrons, and electrons an
isotope has, given its symbol, atomic number, and mass
number.
Describe how the abundance of isotopes affects an element’s
average atomic mass.
ORGANIZATION OF PERIODIC TABLE
In a grocery store you know where everything is
because of the organization. The Periodic Table is
the same way!
 The Periodic Table is organized in a special way.
Elements are arranged by increasing number of
protons.
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PERIODIC LAW
States that elements are arranged in this special
way because similarities in properties will occur.
 Elements that are horizontal are the Period
 Elements that are Vertical in a column are a
Group and also have the same valence electrons.
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USING THE PERIODIC TABLE TO DETERMINE
ELECTRONIC ARRANGEMENT.
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Period: a horizontal row of elements in the periodic table.
Group (family): a vertical column of elements in the
periodic table.
Elements in the same group have
similar properties.
Period
group
SOME ATOMS FORM IONS
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Ionization: the process of adding electrons to or
removing electrons from an atom or group of atoms. For
example, ionization between sodium and chlorine.
Naming atoms that have completed the ionization
process.
Ion: an atom or group of atoms that has lost or gained one or
more electrons and therefore has a net electric charge.
 Cation: an ion with a positive charge. For Example; Na+
 Anion: an ion with a negative charge. For Example; Cl
IONIZATION
Remember what ionization means!
 When ionization occurs the atom no longer has
the same number of electrons and protons and an
ion is formed.
 If an atom loses an electron, it forms a positive
charged ion called a cation.
 Ex. Lithium atom
Lithium ion
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Li+
IONIZATION
If an atom gains an electron it forms a negative
charged ion called an anion.
 Ex. Fluorine atom
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F-
HOW DO THE STRUCTURES OF ATOMS
DIFFER?
As you have seen with sodium and chlorine, atoms of
different elements have their own unique structures.
 Because these atoms have different structures, they
have different properties. See below: it only took one
more or one less to make gold or to make mercury.
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ATOMIC NUMBER EQUALS THE NUMBER
OF PROTONS.
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Atomic number: the number of protons I the
nucleus of an atom.
MASS NUMBER EQUALS THE TOTAL NUMBER
OF SUBATOMIC PARTICLES IN THE NUCLEUS.
Number of
protons in an
atom (atomic
number of the
atom)
Number of
neutrons in an
atom
Mass number of
an atom
ISOTOPES
Isotopes: any atoms having the same number of
protons but different numbers of neutrons.
 For example; Hydrogen has three isotopes all
share similar chemical properties because each is
made of one proton and one electron.
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CALCULATING THE NUMBER OF
NEUTRONS IN AN ATOM
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If you know the atomic number and mass
number of an atom, you can calculate the number
of neutrons it has.
Mass number (A)
 Atomic Number (Z)
 Number of neutrons
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For Example: Uranium has an atomic number of 92
and has a mass number of 235. So, the number of
neutrons must be ?
 Mass number: 235
 Atomic Number: 92
 Number of neutrons: 143
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THE MASS OF AN ATOM
The mass of a single atom is very small.
 Atomic mass unit (amu): a quantity equal to
one-twelfth of the mass of a carbon-12 atom.
 Average atomic mass: the weighted average of
the masses of all naturally occurring isotopes of
an element.
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SECTION 3.2 SUMMARY
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Elements are arranged in
order of increasing atomic
number so that elements
with similar properties are
in the same column, or
group.
Elements in the same group
have the same number of
valence electrons.
Reactive atoms may gain or
lose valence electrons to
corm ions.
An atom’s atomic number is
its number of protons.
An atom’s mass number is
its total number of
subatomic particles in the
nucleus.
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Isotopes of an element have
different numbers of
neutrons, and therefore
have different masses.
An element’s average
atomic mass is weighted
average of the masses of its
naturally occurring isotopes.
SECTION 3.3
FAMILIES OF ELEMENTS
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Section 3.3 Objectives
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Locate alkali metals, alkaline-earth metals, and transition
metals in the periodic table.
Locate semiconductors, halogens, and noble gases in the
periodic table.
Relate an element’s chemical properties to electron
arrangement of its atoms.
HOW ARE ELEMENTS CLASSIFIED?
Elements are classified as metals or nonmetals.
 This classification groups elements that have
similar physical and chemical properties.
 Element Major Groups:
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Metals: the elements that are good conductors of
heat and electricity
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Semiconductors: the elements that are intermediate
conductors of heat and electricity.
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Alkali Metals: the highly reactive metallic elements
located in Group 1 of the periodic table.
Alkaline-earth metals: the reactive metallic
elements located in Group 2 of the periodic table.
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Transition metals: the metallic elements
located in groups 3-12 of the periodic table
NONMETAL: EXCEPT FOR HYDROGEN, NON
METALS ARE FOUND ON THE RIGHT SIDE OF
THE PERIODIC TABLE.
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Nonmetals: the elements that are usually poor
conductors of heat and electricity.
NON METALS INCLUDE SOME ELEMENTS IN
GROUPS 13-16 AND ALL THE ELEMENTS
GROUPS 17-18
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Carbon is found in three different forms and can
also form many compounds.
Glucose
 Chlorophyll
 Isooctane
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Nonmetals and their compounds are plentiful on
Earth
Chlorine is a halogen that protects you from
harmful bacteria
THE NOBEL GAS NEON IS INERT
Nobel (inert) gases: the unreactive gaseous
elements located in Group 18 of the periodic
table.
 Examples of Nobel
 Gases:
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He
Ne
Ar
Kr
Xe
Rn
SECTION 3.3 SUMMARY
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Metals are shiny solids
that conduct heat and
electricity.
Alkali metals, located in
group 1 of the periodic
table, are very reactive.
Alkaline-earth metals,
located in Group 2, are
less reactive than alkali
metals.
Transition metals,
located in Groups 3-12,
are not very reactive.
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Nonmetals usually do
not conduct heat or
electricity.
Nonmetals include the
inert noble gases in
Group 18, the reactive
halogens in Group 17,
and some elements in
Groups 13-16.
Semiconductors are non
metals that are
intermediate conductors
of heat and electricity.
SECTION 3.4
USING MOLES TO COUNT ATOMS
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Section 3.4 Objectives:
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Explain the relationship between a mole of a
substance and Avogadro’s constant.
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Find the molar mass of an element by using the
periodic table.
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Solve problems converting the amount of an element
moles to its mass in grams, and vice versa.
COUNTING THINGS
Eggs are counted by the dozen, peaches are
counted by the bushel, and paper is counted by
the ream.
 There are many different counting units.
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Feet
 Inches
 Miles
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gallons
quarts
meters
The unit used by Scientists to count atoms is the
mole:
Mole: the SI base unit that describes the amount of a
substance. Abbreviated mol.
 Note: A mole is a collection of a very large number of
particles.
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A mole has 602,213,670,000,000,000,000,000 particle
to be exact.
 This long number is usually written as 6.022 x 10 23 /
mole and is referred to as Avogadro’s constant.
 So, if you have 1 mole of gumballs how many
gumballs would you have?
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In chemistry, the conversion factor is molar
mass (the mass of one mole). This value has been
calculated for each element and is usually
included in a periodic table. In most periodic
tables of the elements, the molar mass value is
located in the top right hand corner of an
element's cell.
 The value 55.85 g/mol means that a mole of iron
atoms 6.02 x 1023 (atoms) has a mass of 55.85
grams. In the next lesson, you will see how molar
mass values can be used to convert mole amounts
to mass and vice versa.
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MOLE AND GRAMS ARE RELATED
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The mass in grams of 1 mol of a substance.
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Example 1,
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Example 2:
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1 mol of carbon – 12 atoms has a molar mass of 12.00 g. In
this 1 mol of carbon-12 there is 6.022 x 10 23 carbon-12
atoms / mol.
1 mol of Magnesium has a molar mass of 24.30 g. In this 1
mol of Magnesium there is 6.022 x 10 23 / Magnesium atoms
/ mol.
Let connect how Moles to Grams are related.
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Note: The molar mass of an element in grams is the
same as its average atomic mass in amu. This
information can be found in the periodic table.
CALCULATING WITH MOLES:
Because the amount of a substance and its mass
are related, it is often useful to convert moles to
grams, and vice versa. You can use conversion
factors to relate units. For example; 12 eggs
equal 1 dozen and 12 inches equal 1 foot.
 Conversion factor: a ration equal to one that
expresses the same quantity in two different
ways.
 Converting between the amount of an element in
moles and its mass in grams is outlined below.
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SECTION 3.4 SUMMARY
One mole of a
substance has as
many particles as
there are atoms in
exactly 12.
 Avogadro’s constant,
6.022 x 1023 / mol, is
equal to the number of
particles in one mol of
substance (pure).
 Molar mass is the
mass in grams of 1
mol of a substance.
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An element’s molar
mass in grams is
equal to its average
atomic mass in amu.
 An element’s molar
mass can be used to
convert from amount
to mass, and vice
versa.
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