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6.1
Searching For an Organizing Principle
Searching For an Organizing Principle
How did chemists begin to organize the
known elements?
6.1
Searching For an Organizing Principle
Certain chemical properties are repeating
- reactivity with water (Na, K, etc.)
- reactivity with other elements, etc.
6.1
Searching For an Organizing Principle
Chlorine, bromine, and iodine have very
similar chemical properties.
6.1
Mendeleev’s Periodic Table
Mendeleev
- Arranged elements by properties and atomic mass.
- First example of a Periodic Table of the Elements.
- Mendeleev's approach allowed him to successfully
predict the masses and properties of elements that were
not known at the time he developed his table.
6.1
Mendeleev’s Periodic Table
An Early Version of Mendeleev’s Periodic Table
The Modern Periodic Table
Moseley
- Mendeleev's arrangement was not completely uniform, some elements were
apparently 'out of place'. Note the masses of Te and I in Mendeleev's table.
- Moseley discovered that the nuclear charge increased for each increase of
atomic mass.
- This work provided experimental justification for the modern form of the
Periodic Table.
- This work also resulted in defining atomic number.
The Periodic Law
Moseley's refinement of Mendeleev's table gave us the modern statement of the
Periodic Law.
Periodic Table of the Elements
- Arrangement of elements by atomic number so that elements with similar properties
fall in the same column.
Periodic Law - physical and chemical properties of the elements are periodic functions
of their atomic numbers.
There have been a number of additions to Mendeleev's table since he first proposed it,
but the underlying principle that elements could be arranged by properties is still the
same.
6.1
The Periodic Law
In the modern periodic table, elements
are arranged in order of increasing
atomic number.
6.1
The Periodic Law
The periodic law: When elements are arranged
in order of increasing atomic number, there is a
periodic repetition of their physical and chemical
properties.
• The properties of the elements within a period
change as you move across a period from left
to right.
• The pattern of properties within a period
repeats as you move from one period to the
next.
6.1
Metals, Nonmetals, and Metalloids
Metals, Nonmetals, and Metalloids
What are three broad classes of
elements?
6.1
Metals, Nonmetals, and Metalloids
Three classes of elements are metals,
nonmetals, and metalloids.
Across a period, the properties of elements
become less metallic and more nonmetallic.
6.1
Metals, Nonmetals, and Metalloids
Metals, Metalloids, and Nonmetals in the Periodic Table
6.1
Metals, Nonmetals, and Metalloids
Metals, Metalloids, and Nonmetals in the Periodic Table
6.1
Metals, Nonmetals, and Metalloids
Metals, Metalloids, and Nonmetals in the Periodic Table
6.1
Metals, Nonmetals, and Metalloids
Metals, Metalloids, and Nonmetals in the Periodic Table
6.1
Metals, Nonmetals, and Metalloids
Metals
Metals are good conductors of heat and electric
current.
• 80% of elements are metals.
• Metals have a high luster, are ductile, and are
malleable.
6.1
Metals, Nonmetals, and Metalloids
Uses of Iron, Copper, and Aluminum
6.1
Metals, Nonmetals, and Metalloids
Uses of Iron, Copper, and Aluminum
6.1
Metals, Nonmetals, and Metalloids
Uses of Iron, Copper, and Aluminum
6.1
Metals, Nonmetals, and Metalloids
Nonmetals
In general, nonmetals are poor conductors of
heat and electric current.
• Most nonmetals are gases at room
temperature.
• A few nonmetals are solids, such as sulfur
and phosphorus.
• One nonmetal, bromine, is a dark-red liquid.
6.1
Metals, Nonmetals, and Metalloids
Metalloids
A metalloid generally has properties that are
similar to those of metals and nonmetals.
The behavior of a metalloid can be controlled by
changing conditions.
6.1
Metals, Nonmetals, and Metalloids
If a small amount of boron is mixed with silicon,
the mixture is a good conductor of electric
current. Silicon can be cut into wafers, and used
to make computer chips.
6.2
Classifying the Elements
A coin may contain much
information in a small
space—its value, the year it
was minted, and its country
of origin. Each square in a
periodic table also contains
information. You will learn
what types of information
are usually listed in a
periodic table.
6.2
Squares in the Periodic Table
Squares in the Periodic Table
What type of information can be displayed in a
periodic table?
6.2
Squares in the Periodic Table
The periodic table displays the symbols and
names of the elements, along with information
about the structure of their atoms.
6.2
Squares in the Periodic Table
The background colors in the squares are used
to distinguish groups of elements.
• The Group 1A elements are called alkali
metals.
• The Group 2A elements are called alkaline
earth metals.
• The nonmetals of Group 7A are called
halogens.
6.2
Squares in the Periodic Table
6.2
Electron Configurations in Groups
Electron Configurations in Groups
How can elements be classified based on their
electron configurations?
6.2
Electron Configurations in Groups
Elements can be sorted into noble gases,
representative elements, transition metals, or
inner transition metals based on their electron
configurations.
6.2
The blimp contains
helium, one of the noble
gases.
Electron Configurations in Groups
6.2
Electron Configurations in Groups
The Noble Gases
The noble gases are the elements in Group 8A
of the periodic table. The electron configurations
for the first four noble gases in Group 8A are
listed below.
6.2
Electron Configurations in Groups
The Representative Elements
Elements in groups 1A through 7A are often
referred to as representative elements because
they display a wide range of physical and
chemical properties.
• The s and p sublevels of the highest occupied
energy level are not filled.
• The group number equals the number of
electrons in the highest occupied energy level.
6.2
Electron Configurations in Groups
In atoms of the Group 1A elements below, there
is only one electron in the highest occupied
energy level.
6.2
Electron Configurations in Groups
In atoms of the Group 4A elements below, there
are four electrons in the highest occupied energy
level.
6.2
Representative Elements
Representative Elements
6.2
Representative Elements
Representative Elements
6.2
Representative Elements
Representative Elements
6.2
Representative Elements
Representative Elements
6.2
Transition Elements
Transition Elements
There are two types of transition elements—
transition metals and inner transition metals.
They are classified based on their electron
configurations.
6.2
Transition Elements
In atoms of a transition metal, the highest
occupied s sublevel and a nearby d sublevel
contain electrons.
In atoms of an inner transition metal, the
highest occupied s sublevel and a nearby f
sublevel generally contain electrons.
6.2
Blocks of Elements
Transition Elements
6.3
Trends in Atomic Size
Trends in Atomic Size
What are the trends among the elements for
atomic size?
6.3
Trends in Atomic Size
The atomic radius is one half of the distance
between the nuclei of two atoms of the same
element when the atoms are joined.
6.3
Trends in Atomic Size
Group and Periodic Trends in Atomic Size
• In general, atomic size increases from top to
bottom within a group and decreases from left
to right across a period.
6.3
Trends in Atomic Size
6.3
Trends in Atomic Size
Atomic radius
Defined as one-half the
distance between nuclei of
identical atoms joined in a
molecule.
Across period - as Z
increases, n remains the
same. Increased attraction
of electrons in same n.
Remember n gives some
indication of location of
electrons from nucleus.
Down group - Z increases, so
does n. Electrons are
farther away from positive
nucleus, attractive force
for valence electrons
decreases.
6.3
Ions
Some compounds are composed of particles
called ions.
• An ion is an atom or group of atoms that has
a positive or negative charge.
• A cation is an ion with a positive charge.
• An anion is an ion with a negative charge.
6.3
Ions
How do ions form?
Ions
6.3
Ions
Positive and negative ions form when
electrons are transferred between atoms.
6.3
Ions
Positive and negative ions form when
electrons are transferred between atoms.
6.3
Trends in Ionization Energy
The energy required to remove an electron from
an atom is called ionization energy.
• The energy required to remove the first
electron from an atom is called the first
ionization energy.
• The energy required to remove an electron
from an ion with a 1+ charge is called the
second ionization energy.
6.3
Trends in Ionization Energy
Group and Periodic Trends in Ionization Energy
First ionization energy tends to decrease from
top to bottom within a group and increase from
left to right across a period.
6.3
Trends in Ionization Energy
6.3
Trends in Ionization Energy
6.3
Trends in Ionization Energy
Ionization Energy (IE)
Defined as the amount of energy necessary to remove electrons
from an element in the gaseous state.
First Ionization
A + energy → A+ + eAcross period - increasing Z, increasing IE, e - held 'tightly'
Down group - increasing Z, decreasing IE, e - less tightly held
Higher Ionization Energies
A + energy → Ab+ + beb - number of the ionization
What is the reason for some of the other variations in ionization
energies?
Large jump between 1st and 2nd in Na
Large jump between 2nd and 3rd in Mg
Check out changes in electronic configurations.
6.3
Trends in Ionic Size
Trends in Ionic Size
During reactions between metals and
nonmetals, metal atoms tend to lose electrons,
and nonmetal atoms tend to gain electrons. The
transfer has a predictable effect on the size of
the ions that form.
6.3
Trends in Ionic Size
Cations are always smaller than the
atoms from which they form. Anions are
always larger than the atoms from
which they form.
6.3
Trends in Ionic Size
Relative Sizes of Some Atoms and Ions
6.3
Size generally increases
Trends in Ionic Size
Trends in Ionic Size
6.3
Trends in Electronegativity
Trends in Electronegativity
Electronegativity is the ability of an atom of an
element to attract electrons when the atom is in a
compound.
• In general, electronegativity values decrease
from top to bottom within a group. For
representative elements, the values tend to
increase from left to right across a period.
6.3
Trends in Electronegativity
Representative Elements in Groups 1A through 7A
Electronegativity (Pauling Scale)
Measure of the ability of an atom to attract
electrons
This does not necessarily mean anything about
reactivity under a given set of conditions.
F - has the highest
Fr - has the lowest
Electronegativity also gives an indication of the
tendency of atoms to form cations or
anions. High electronegativity usually means
an atom will favor forming anions.
Atoms tend to form ions in an effort to attain a
valence electronic configuration that is
isoelectronic with a Noble gas.
6.3
Summary of Trends
Summary of Trends
What is the underlying cause of periodic
trends?
6.3
Summary of Trends
The trends that exist among these
properties can be explained by
variations in atomic structure.
6.3
Summary of Trends
Increases Decreases
Size
Electronegativity
Ionic
Atomic
Nuclear
Shielding
Ionization
of
size
cations
Size
anions
Charge
energy
Increases
Decreases
Constant