Development of the Periodic Table

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Development of the Periodic Table
In this presentation you will

• explore how the periodic table was developed

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Introduction
The modern periodic table is well knownto all
studying chemistry.
It arranges the known elements into both columns
(groups) and rows (periods).
The periodic table reflects both the atomic mass,
and the electron structure of elements.
How did this table come about?
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Discovery of Elements
Element Symbol
copper Cu
arsenic As
gold Au
silver Ag
tin Sn
carbon C
bismuth Bi
antimony Sb
mercury Hg
sulfur S
lead Pb
Iron Fe
phosphorous P
There were so few elements (less than 15) known
before 1700 that a table wasnt needed.
The known elements at this stage were primarily
metals that could be easily extracted.
Iron, copper, silver, gold, tin, lead, and
mercury were all known and used.
In addition carbon, sulfur, bismuth, antimony,
phosphorous, and arsenic were known.
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Discovery of Elements
During the next 100 years, 15 more elements were
discovered.
Element Symbol
titanium Ti
chromium Cr
molybdenum Mo
tungsten W
manganese Mn
cobalt Co
nickel Ni
nitrogen N
oxygen O
beryllium Be
chlorine Cl
strontium Sr
platinum Pt
yttrium Y
zinc Zn
These are shown in the table.
After 1800, the rate of discovery increased, so
that another 53 elements were added up to 1900.
There was now a need to arrange these elements in
a table.
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Question 1
There are over 100 elements in the modern
periodic table. Before 1700, how many had been
identified?
A) Less than 15
B) Less than 49
C) More than 50
D) More than 100
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Question 1
There are over 100 elements in the modern
periodic table. Before 1700, how many had been
identified?
A) Less than 15
B) Less than 49
C) More than 50
D) More than 100
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Early Attempts to Group Elements
We now know that the key property used to arrange
the elements is their atomic mass.
If only John Dalton had realized that, when he
proposed his theory of atomic structure in 1799.
His measurements of the mass of elements was not
very convincing, and did not show patterns.
Other scientists rejected the concept, misled by
the inaccurate measurements.
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Early Attempts to Group Elements
When Berzelius came up with a more accurate
analysis in 1828, it was rejected, since Daltons
earlier similar proposal had already been
discredited.
Li Na K
C N O
Ca Sr Ba
Cl Br I
Other attempts to bring order, started to look at
the physical and chemical properties of the
elements.
In 1817, Dobereiner suggested that elements could
be put into groups of three.
His triads all had a similar appearance and
reacted similarly.
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Dobereiners Triads
Dobereiner noticed that if he took his triads,
and compared their relative atomic mass (the mass
number), there was a pattern.
Element Atomic mass
Li 7
Na 23
K 39
His first triad was lithium, sodium, and
potassium.
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Dobereiners Triads
They are all soft metals that react with water,
to give alkalis.
Element Atomic mass
Li 7
Na 23
K 39
When he looked at their atomic masses, he saw
that the atomic mass of sodium (the middle
element) was the average of the sum of all their
atomic masses.
Sum 39 23 7 69
Average 69 3 23
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Dobereiners Triads
His second triad was chlorine, bromine, and
iodine.
Element Atomic mass
Cl 35.5
Br 80
I 127
Chlorine and bromine are gases, while iodine is a
solid. They are all colored.
Sum 35.5 80 127 242.5
They all react easily to form their salts
(chloride, bromide, and iodide).
Average 242.5 3 80.8
The average isnt perfect, but it is close.
Unfortunately, he could not get all the known
elements into triads.
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Question 2
What chemical property did Dobereiner use to
group Li, Na, and K?
A) They were all soft
B) They were all metallic
C) They all had related atomic masses
D) They all reacted with water to produce an
alkali
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Question 2
What chemical property did Dobereiner use to
group Li, Na, and K?
A) They were all soft
B) They were all metallic
C) They all had related atomic masses
D) They all reacted with water to produce an
alkali
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Other Theories The Telluric Spiral
In 1862, de Chancourtois proposed, a spiral table
based on the element tellurium.
He plotted the atomic weight of each element in a
spiral. One complete turn of the spiral was equal
to an increase of 16 in the atomic weight.
Unfortunately it was badly presented, and lacked
a diagram it was largely unrecognized.
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Other Theories Newlands Octaves
John Newlands arranged all the elements known in
1864, in order of their relative atomic mass.
He noted that each element had similar properties
to the element that was eight places further on.
For example, sodium was eight places on from
lithium, and potassium was eight places on from
sodium.
Note a musical octave has eight notes
As he hadnt allowed for undiscovered elements
there were too many exceptions for it to gain
acceptance from other scientists.
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Mendeleev and Meyer
The first universally accepted periodic table was
drawn up by Dimitri Mendeleev in 1869.
He just beat Julius Meyer to publication, so it
is Mendeleevs name that is usually associated
with the first periodic table.
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Mendeleev and Meyer
Meyer had plotted physical properties of the
known elements against their atomic mass, and
shown convincingly, that periodicity existed.
Mendeleev had done the same, but he had also
shown that there were missing elements that had
yet to be discovered.
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Mendeleev
Not only did Mendeleev identify elements still to
be discovered, he also predicted their properties.
In 1895 and 1896, two of the missing elements,
germanium and gallium, were discovered.
Their properties matched the predicted properties.
Mendeleev therefore strengthened his theory, and
assured that it was his name associated with the
discovery of the periodic table.
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Physical and Chemical Properties
Mendeleev also produced a critique of why it was
the atomic weight that was the significant
property to order the table, and not others that
had been tried in the past.
Property Metals/non-metalsFormation of
acidic/basic oxidesReaction with
oxygen/hydrogenElectrochemical
sequenceValenceColorOpticalElectrical
Magnetic
A list of some of the other properties is shown
in the table.
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Physical and Chemical Properties
In all cases, Mendeleev dismisses the
relationships on the grounds of too many
exceptions or difficulties in accurately
establishing the properties reliably.
Property Metals/non-metalsFormation of
acidic/basic oxidesReaction with
oxygen/hydrogenElectrochemical
sequenceValenceColorOpticalElectrical
Magnetic
One example phosphorous exists in two forms.
One is metallic and the other is not.
Is phosphorous metallic or not?
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Post Mendeleev Developments
In 1894, Lord Rayleigh and Sir William Ramsay
discovered Argon, one of the noble gases. They
proposed adding a new group, group 18.
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Post Mendeleev Developments
In 1911, Henry Moseley analyzed the spectra of 38
metals. He found that the pattern was better if
they were arranged in order of their atomic
numbers (the number of protons in the nucleus).
When the elements were all arranged in this way,
it resolved a few minor issues, and caused one or
two elements to swap places.
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Post Mendeleev Developments
Many new elements have been artificially
synthesized.
The lanthanide and actinide groups were separated
into a sub-table in the 1960s.
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Question 3
What was the crucial advantage Mendeleev had over
Meyer in developing the periodic table?
A) Mendeleev used all the known elements, Meyer
didnt
B) Mendeleev explained why other properties could
not be used, Meyer didnt
C) Mendeleev predicted the properties of missing
elements, Meyer didnt
D) Meyer published first, Mendeleev was able to
overcome the criticisms Meyers work received
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Question 3
What was the crucial advantage Mendeleev had over
Meyer in developing the periodic table?
A) Mendeleev used all the known elements, Meyer
didnt
B) Mendeleev explained why other properties could
not be used, Meyer didnt
C) Mendeleev predicted the properties of missing
elements, Meyer didnt
D) Meyer published first, Mendeleev was able to
overcome the criticisms Meyers work received
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Summary
In this presentation you have seen

• how the periodic table was developed

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