Transcript 17.3: The Periodic Table

17.3:
The Periodic Table
Some Early Ideas About
Elements
Traditionally, early Greeks considered that there
were four classical elements: earth, air, fire,
and water.
Some Early Ideas About
Elements
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Later, around 1667, it was thought there was
the existence of, in addition to the classical
four elements of the Greeks, an additional
fire-like element called “phlogiston” that was
contained within combustible (burnable) or
rustable bodies, and released during
combustion or rusting .
The theory was an attempt to explain
oxidation processes such as combustion and
the rusting of metals.
What the heck is
“phlogiston?”
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The phlogiston theory from 1667 viewed
phlogiston as a component of matter.
The burning or rusting of a material was
considered to be the escaping of phlogiston
from the matter.
If a material did not burn or rust, it was
considered to contain no phlogiston.
Discovery of Modern Elements
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In the late 1700s, Antoine
Lavoisier of France suggested
that burning was actually a
chemical combination with
oxygen.
Lavoisier realized that there
needed to be a new concept of
elements, compounds, and
chemical change.
What we now know . . .
at least, for now.
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We now know that there are 89 naturallyoccurring elements and at least 23 short-lived
and artificially prepared elements.
The elements of the periodic table are
believed to be all the elements that exist in the
universe!
 Click here to see how we know:
http://spiff.rit.edu/classes/phys301/lectures
/spectra/spec_proper_orientation.gif
Naming the Elements
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The first 103 elements have internationally
accepted names, which can come from:
 an unusual or identifying property of the
element.
 places, cities, and countries.
 famous scientists.
 Greek mythology.
 Astronomical objects.
The elements of aluminum, Iron, Oxygen, and
Silicon make up about 88 percent of the earth's
solid surface.
 Water on the surface and in the air as clouds
and fog is made up of hydrogen and oxygen.
 The air is 99 percent nitrogen and oxygen.
 Hydrogen, oxygen, and carbon make up 97
percent of a person.
 Thus almost everything you see in this picture
is made up of just seven elements.
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Along Came
Mendeleev . . .
 Dmitri Mendeleev was born in 1834 in
Siberia, the youngest of 14 children, and
he died in 1907.
 He gave us a functional scheme with
which to classify elements.
Dmitri Mendeleev: Father
of the Periodic Table
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HOW HIS WORKED…
Put elements in rows by increasing atomic
mass
.
SOME
PROBLEMS…
Put had
elements
in columns
by the
they
He
to leave
blank spaces
forway
what
he said
were
undiscovered elements. (Turned out he was
reacted.
right!)
He was able to predict properties of
He
broke the pattern
of increasing atomic weight
undiscovered
elements.
to keep similar reacting elements together.
Mendeleev’s
Periodic Table
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Scientists have since
discovered the missing
elements and found
that their properties
were close to what
Mendeleev had
predicted.
On March 6, 1869, he
presented his periodic
table to the scientific
community.
Improvements
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Mendeleev wasn’t too far off.
In 1913, Henry Moseley of England put
elements in rows by increasing ATOMIC
NUMBER instead of increasing atomic mass!!
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If you look at cobalt and nickel, even though
cobalt has fewer protons, its average atomic
mass is greater than nickel’s.
Seaborgium and bohrium are the same way.
Groups or Families
Groups are columns of the periodic table.
 Columns are vertical, like columns that
hold up a porch roof.
 Elements in the same group have similar
chemical and physical properties!!
(Mendeleev did that on purpose.)
 Families have the same number of
valence electrons.
 They will form the same kinds of ions
(charged particles) and react similarly.
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 Valence electrons
are the electrons in
the outside energy
level of an atom.
 They are
responsible for
the bonding of
one atom to
another.
Valence
Electrons
http://www.chemicalelements.com/index.html
Valence
Electrons
Families on the Periodic Table
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Families may be one
column, or several
columns put together.
Families often have
names rather than
numbers (just like
some families have a
common last name).
http://www.periodicvi
deos.com/
Electron Dot Diagrams
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Another way to draw an atom model is with an
electron dot diagram, or Lewis Structure.
They simply use the symbol of the element and
the number of valence electrons that element
has.
All atoms become stable when they bond with
another so that their outside energy level
becomes stable.
They become stable when they have eight
valence electrons in their outside energy level.
Elements generally stop bonding with others
when they have eight electrons in the outermost
energy level. This is called the “Rule of Octet.”
Rows on the Periodic Table
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Rows are also called periods, and they are
horizontal.
The row an element is in tells you how many
energy levels it has.
There are up to 7 energy levels.
Forming Ions
Sodium (Na +)
Chlorine (Cl-)
Using Dot Diagrams to
Show Bonding
Na Cl
[Na]+ [ Cl ]-
• Sodium has one valence electron.
• Chlorine has 7 valence electrons.
• When they bond, you can see how chlorine
now has a stable outer shell.
• You also know sodium is now stable since it
got rid of its single valence electron.
Regions on the Table
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Elements on the upper right side of the
periodic table—AND hydrogen—are
nonmetals.
Elements on the left hand side—EXCEPT
hydrogen—are metals.
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That includes the rows at the very bottom.
A zigzag line separates the metals from the
nonmetals.
Many of the elements touching the zigzag
line are called metalloids.
Elements in the Universe
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Hydrogen is the most abundant element in the
universe.
Hydrogen, along with helium, form the building
blocks of the larger elements.
The largest of the elements (the ones with the
most protons) are believed to be formed in
supernovas and flung out into space.
Supernovas are stars that explode with a great
deal of heat and energy.
Elements with an atomic number above 92, AND
Pm (61), and Tc (43) are rare or nonexistent on
Earth.
They have been detected using a telescope with
a spectrometer.
Visible Spectra of Known Elements