The Periodic Table
The Chemist’s, Chemistry Teacher’s, Chemistry
Student’s Best Friend
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Poetry Assignment
• Pick an element
• Write a poem about it without using its
name
• Read the poem to the class and see if we
can figure it out!
What is the Periodic Table?
• The periodic table is an organized
arrangement of the elements
• Over time, and as more elements were
discovered, scientists noticed repeating
patterns of properties among elements
• They tried to organize the elements by these
properties
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JOHANN DOBEREINER (1829)
The Model of Triads
• Classified some elements into groups of three, which
he called triads
• The elements in a triad had similar chemical
properties and orderly physical properties
• One element in each triad had properties
intermediate of the other two elements
• Examples:
– Cl, Br, I
– Ca, Sr, Ba
4
JOHN NEWLANDS (1863)
The Law of Octaves
• Arranged elements in order of increasing atomic mass
• Noticed that certain properties repeated every eighth
element
• Elements should be arranged in “octaves” (like in music)
• His law of octaves failed beyond the element calcium
• His claim was dismissed out of hand
• But this idea of “repeating 8’s” will re-surface!
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DMITRI MENDELEEV (late 1800’s)
• He is credited with “inventing” the periodic table, although
other folks were also doing similar work around the same
time
• He arranged the known elements by increasing atomic mass
• When arranged this way, he noticed that properties did
repeat
• He left blank spaces to keep elements properly aligned by
their properties
• He felt that the blank spaces would someday be occupied by
elements that had not yet been discovered
• He predicted the properties of those elements –
his predictions were remarkably accurate
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But Mendeleev’s Periodic Table
Was Not Perfect …
• In spite of his great achievement, problems arose
when new elements were discovered and more
accurate atomic weights determined
• Examples:
– Ar and K
– Co and Ni
– Te and I
– Th and Pa
7
HENRY G.J. MOSELEY (1913)
• The old arrangement was not perfect – some
elements just didn’t fit
• Improved the periodic table by arranging elements
by atomic number instead of atomic mass
• For the most part, atomic masses also increase,
although there are some exceptions (examples are
cobalt and nickel)
• The new arrangement corrected the problems from
the old version
• Current arrangement of periodic table is by atomic
number
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Sad Ending …
• Henry Moseley was killed by a
sniper in 1915 during World War I
(Gallipoli, Turkey)
• Because of this, the British government
changed its policy and did not allow
“prominent and promising scientists” to enlist
for combat duty in the armed forces during
World War II
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The Periodic Law:
When elements are arranged in order of
increasing atomic number, there is a
periodic repetition of their physical and
chemical properties
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Periodic or cyclical events
• Can you think of some examples of
phenomena or events that are periodic or
cyclical?
•
•
•
•
•
Seasons
Weeks
Phases of the moon
Octaves in music
Waves
Let’s pretend we
are Mendeleev’s
partner trying to
figure out the
periodic table!
EXAMPLE PERIODIC TABLE
ENTRY
Note that the atomic number is a whole #
and the atomic mass is a decimal #
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NOMENCLATURE OF ELEMENTS –
CHEMICAL SYMBOLS
• Could be the 1st letter of the element – H=hydrogen
• May need the 2nd or another letter of the element –
C=carbon, so what about cobalt or calcium? Needed
2nd letter. What about chlorine? 6 elements have “C”
as 1st letter!
• Some derived from Latin name – Au=gold (aurum =
shining dawn)
• Some named to honor scientists (Cm=curium for
Marie Curie)
• Some named for planets (U=uranium,
Np=neptunium, Pu=plutonium)
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NOMENCLATURE OF ELEMENTS –
CHEMICAL SYMBOLS
• Some named for places (Eu = Europium, Ytterby in
Sweden has four elements named for it: Tb =
terbium, Y = yttrium, Er = erbium, Yb = ytterbium)
• Some named for properties (Cs = cesium because it
imparts a blue color to a flame, caesius = sky blue)
• Some named using rules established by an
international committee
• First letter is ALWAYS capitalized; second letter is
ALWAYS lower case
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Trivia Question:
What is the only letter of the
alphabet not to appear in the
periodic table?
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Trivia Question:
What is the only letter of the
alphabet not to appear in the
periodic table?
J
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There are many ways to “slice
up” the periodic table
Let’s look at some of them …
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One way to examine the periodic table –
Break it up element type
What’s up with the heavy black line?
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Metals, Non-Metals, Metalloids
• That heavy stair-step line separates the
metals from the non-metals
• The elements that straddle the line are called
“metalloids”
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Properties of Metals
• Metals are good conductors
of heat and electricity
• Metals are shiny
• Metals are ductile (can be
stretched into thin wires)
• Metals are malleable (can be
pounded into thin sheets)
• A chemical property of metal
is its reaction with water,
which results in corrosion
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Properties of Non-Metals
• Non-metals are poor
conductors of heat and
electricity
• Non-metals are not ductile or
malleable
• Solid non-metals are brittle
and break easily
• They are dull (non-lustrous);
they do not reflect light
• Some non-metals are gases
(O, N, Cl); some are brittle
solids (S); one is a orange
liquid (Br)
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Properties of Metalloids
• Metalloids (metal-like) have
properties of both metals and nonmetals
• Some of the metalloids are semiconductors. This means that they
can carry an electrical charge
under special conditions. This
property makes metalloids useful
in computers and calculators
• They are solids that can be shiny
or dull
• They conduct heat and electricity
better than non-metals but not as
well as metals
• They are ductile and malleable 22
Another Way to Divvy Up the
Periodic Table
What about rows and columns?
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Rows on the Periodic Table
• Each horizontal row of the periodic table is called a
period
– There are 7 periods
– The elements in a period are not alike in
properties
– The properties change greatly across even given
row
– The first element in a period is always an
extremely active solid; the last element in a period
is always an inactive gas
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Columns on the Periodic Table
• The vertical columns of elements on the periodic
table are called groups or families
– The elements in any group/family of the periodic
table have similar, but not identical, physical and
chemical properties
– Groups/Families have names in addition to numbers
– Groups/Families are numbered from 1-18 (left-right)
or I-IIA, B, III-VIIIA (left-right)
– The elements in each column have the same number
of electrons in the outermost energy level or shell
(one to eight → remember John Newland’s “law of
octaves”?)
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Elements Investigation Lab
• Now’s it is your turn to get to see some of
these elements up close and personal
• You and a partner will visit a
representative sample of elements and
record physical information about each
Let’s Explore Yet Another Way to
Divvy Up the Periodic Table
- by Families!
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GROUP 1 - ALKALI METALS
•Group 1
•very reactive metals
that do not occur
freely in nature
•malleable, ductile,
good conductors of
heat and electricity.
•can explode if they
are exposed to water
Alkali Metals
Alkali Metals
• The alkali metals form compounds that are
similar to each other.
• Alkali metals each have one valence electron
• This electron is removed when alkali metals
react.
• The easier it is to remove an electron, the
more reactive the atom is.
• TREND: Reactivity of alkali metals increase
as you go down the group.
ALKALINE EARTH METALS
•Group 2
•metals
•very reactive
•not found free
in nature
Alkaline Earth Metals
• Alkaline Earth metals each have
TWO valence electrons
• These electrons are removed
when alkaline earth metals react.
• The easier it is to remove an
electron, the more reactive the
atom is.
• TREND: Reactivity of alkali metals
increase as you go down the
group.
TRANSITION METALS
•Group 3-12
•ductile and
malleable, and
conduct electricity
and heat
•iron, cobalt, and
nickel, are the only
elements known to
produce a magnetic
field.
RARE EARTH ELEMENTS
•many are man-made
From www.science-class.net
Boron, Carbon, Nitrogen
& Oxygen Families
Named after the head of each family
These elements are usually referred as either metals,
metalloids or non metals rather than their family names
P-block METALS
•are ductile
and malleable
•are solid, have
a high density,
HALOGENS – Group 17
•Group 17
•"halogen" means "salt-former" and
compounds containing halogens are
called "salts"
•exist in all three states of matter
Halogens – group 17
• Fluorine is the most
reactive of the halogens
because its outer energy
level is closest to the
nucleus.
• The reactivity of the halogens decreases
down the group as the outer energy levels of
each element’s atoms get farther from the
nucleus.
NOBLE GASES
•Group 18
•do not form compounds easily
•Happy/Inert Elements (Full outer shells)
From www.science-class.net
Noble gases – group 18
• Neon and the
elements below it in
Group 18 have eight
electrons in their
outer energy levels.
• Their energy levels
are stable, so they
do not combine
easily with other
elements.
Noble gases
• At one time these elements were thought
to be completely unreactive, and therefore
became known as the inert gases.
• When chemists learned that some of these
gases can react, their name was changed to
noble gases.
• They are still the most stable element group.
Coloring Activity
• Okay…need a way to organize all of this
information I just gave you?
• You and a partner will now work on the
Getting to know the Periodic Table
Coloring Activity