Download Chemistry 1 Chapter 4, The Periodic Table

Chapter 6
The Periodic Table
J. W. Dobereiner
In 1829
-organized elements into “triads” (a group
of 3 elements with similar properties)
•History
• John Newlands in 1865
– He was the first to arrange the elements
according to their properties
– arranged the known elements according to
their properties and in order of their increasing
atomic mass
– He place the elements in a table and he
noticed that all of the elements in a given row
had similar properties and these properties
seemed to repeat every 8 elements, so he
called this pattern the law of octaves
•Dmitri Mendeleev in 1869
•used Newlands observation and other
information to produce the first orderly arrangement of
all the elements known at the time (63 elements)
•this arrangement is called a periodic table
•He arranged the elements in order of increasing
atomic mass
•he started a new row every time he noticed the
properties repeated placing elements in the new
row directly below elements of similar properties
in the preceding row
•Dmitri Mendeleev, continued
•Mendeleev’s table contained gaps
•he explained these gaps by predicting that there
were undiscovered elements
•he also predicted the properties of these missing
elements based on the column they were in
•Dmitri Mendeleev, continued
•he also noticed that some elements
didn’t fit in the correct column by property when
ordering them by atomic mass
• he switched the order of these elements to
group the elements in the column that matched
their properties
•at first he thought the atomic masses must have
been incorrect, but they were correct, so
Mendeleev couldn’t explain this irregularity
•Henry Moseley - about 40 years after
Mendeleev’s periodic table was published
• found a different physical basis for the
arrangement of the elements, discovered
atomic number
• He studied the Xrays of different elements and
found that they each had unique wavelengths
that correlate to the number of protons in the
element this number is now referred to as the
atomic number
•Henry Moseley, continued
• when the elements were arranged in the
periodic table by atomic number rather than
atomic mass, the discrepancies Mendeleev
found were no longer there
• Moseley’s work led to the modern definition
of atomic number and showed that atomic
number is the basis for organization of the
periodic table not atomic mass
•The Physical Basis of the Periodic Table
• The Periodic Law states: the repeating
properties of elements change periodically with
their atomic number
•Organization of the Periodic Table
•elements in each column have the same number
of electrons in their outer level
•This is why they have similar properties
•We can use this to predict the ending electron
configurations on the s and p blocks
•outer electrons are called valence electrons
• it is the valence electrons that participate in
chemical reactions, so elements with the same
number of valence electrons tend to react in a
similar fashion
•That is why groups of elements in the same
column share certain properties
•Arrangement on the Periodic Table
• vertical columns are called groups and
horizontal rows are called periods
• certain groups have specific names and we call
them families
• elements in the same period have the same
number of occupied energy levels (1-7)
• label these levels on the periodic table
• we can use the period numbers and ending
electron configurations for the groups to predict
an elements electron configuration
•The Main-Group Elements
• Elements in groups 1,2 and 13-18 are called
the main-group elements
• they are in the s and p blocks, meaning they are
adding electrons to their s and p sublevels
respectively
• their electron configurations are regular and
consistent
•Remember, the elements in each group have
the same number of valence electrons and
therefore the same ending configuration
•groups with family names
• group 1 – alkali metals, they have a single
valence electrons and are very reactive
• they are never found in nature as pure
elements because they are so reactive they
are always combined with other elements
as compounds
•group 2 – alkaline-earth metals, they have 2
valence electrons, they must lose 2 electrons to
have a stable configuration, they are slightly less
reactive than the alkali metals
•they are usually found in nature as
compounds rather than pure elements
•groups with family names, continued
• group 16 – chalcogens, they have 6 outer
electrons and are relatively reactive
•group 17 – halogens, the most reactive group of
nonmetals, they have 7 outer electrons, they often
gain one electron
•group 18 – noble gases, have a full set of outer
electrons, these elements are very stable, they
rarely react, they are also known as inert gases
•These groups are all nonmetals
•Helium is the only noble gas that has only 2 outer
electrons
-because it is in the first level, and 2 is the
maximum number of electrons that level 1
can hold
-so it has a full outer level
• Hydrogen is in a class by itself
• it is the most common element in the
universe
• it consists of only one proton and one
electron , so it behaves differently than any
other element
• it can react with many other elements
•Most Elements are Metals
• when looking at the periodic table; metals are on
the left, nonmetals are on the right, and the majority
of elements are metals
•there is a general dividing line, called the staircase
line, which separates metals and nonmetals
•elements along the staircase line that have
properties of both metals and nonmetals are referred
to as metalloids
•Metals Share Many Properties
• most metals are shiny (not all, and there are some
nonmetals that are shiny)
• all metals conduct electricity (this is one property
that distinguishes between metals and nonmetals)
• metals are conductors of heat (there are some
nonmetals that do this)
• metals are ductile (can be squeezed out into a wire)
• metals are malleable (can be hammered or rolled
into sheets)
•Metals Share Many Properties, continued
• Other Properties of Metals
– metals can be mixed with one or more other
elements (usually metals) to form alloys
• this mixing eliminates some of the
disadvantages of the
• independent elements and gives the new
alloy properties that are different than the
original elements
• Ex. – Brass is a yellowish alloy of copper and zinc,
sometimes including small amounts of other
metals, but usually 67 percent copper and 33
percent zinc.
•Transition Metals
• groups 3-12 are referred to as transition
elements
• they are the d group elements, therefore
some of them have “irregular” electron
configurations
• they do not always have identical
electron configurations within the
same group
•Transition Metals, continued
• even if these elements do not have the
same electron configurations within a
group, there is a pattern to there outer
electron configs
– the sum of the outer d and s electrons is
equal to the group number
• transition metals are generally less
reactive than the alkali and alkaline-earth
metals
– some transition metals are so unreactive that
they rarely form compounds with other
elements
•Properties of Nonmetals
• generally gases or brittle solids at room
temperature
• if they are solid their surfaces are dull
• they are insulators
•Lanthanides and Actinides
• there are 2 periods at the bottom of the periodic
table, they are referred to as a series
•the top period is called the lanthanide series
because it follows the element lanthanum
•their atomic numbers range from 58-71
•they are adding electrons to the 4f orbitals
•the bottom period is called the actinide series
because it follows the element actinium
•their atomic numbers range from 89-103
•they are adding electrons to the 5f orbitals
• they are all radioactive
•Trends in the Periodic Table
• Ionization Energy
•the energy required to remove an electron
from an atom is called the ionization energy
•Decreases as You Move Down a Group
•the further down the table you go, the more
energy levels you add
•therefore, the pull from the nucleus is less
due to the increased distance and the electron
shielding affect (the inner electrons shield the
outer electrons from the nucleus)
•Ionization Energy, continued
•
Increases as You Move Across a Period
–
–
from left to right across the periodic table,
you are adding one proton in the nucleus
and one electron in the same outer level
this additional positive charge allows the
nucleus to pull harder on the electrons, and
the electrons are being added in the same
level so the electron shielding is not
increasing
•
Atomic Radius
•
the size of an atom from its center to the outer
edge of its cloud
• Increases as You Move Down a Group
•as you move down the table you are adding
additional levels, this increases the size of the
cloud
•
Atomic Radius, continue
–
Atomic Radius Decreases as You Move
Across a Period
•
from left to right across the periodic table,
you are adding one proton in the nucleus
and one electron in the same outer level
•
this additional positive charge allows the
nucleus to pull harder on the electrons
and decrease the size of the cloud
•
Electronegativity
–
atoms often bond together to form compounds, these
bonds sometimes involve the sharing of electrons
•
this sharing is not always equal, one atom sometimes
pulls the electrons harder than the other
numerical values called electronegativities reflect how a
bonded atom attracts the shared electrons
•
the atom with the highest electronegativity value will
pull on the electrons harder than the other atom
•
Fluorine is the element with the highest value and it is 4
–
•
Electronegativity, continued
–
Decreases as You Move Down a Group
• as you move down the table you are
adding additional levels, this makes the
distance and between the outer electrons
and the nucleus more and increases the
shielding affect
• these two things account for the less pull
from the nucleus
•
Electronegativity, continued
–
Increases as You Move Across a Period
• from left to right across the periodic table,
you are adding one proton in the nucleus
and one electron in the same outer level
• this additional positive charge allows the
nucleus to pull harder on the electrons as
the shielding affect stays the same;
therefore the nucleus can pull harder on
the outer electrons
–
Electron Affinity
•
•
•
•
relates to a non-bonded atoms attraction for
electrons
the energy that occurs when a neutral atom
gains an electron
decreases as you move down the table for the
same reasons of electronegativity
increases as you move across the table for the
same reasons of electronegativity