The History of the Modern Periodic Table

1
The History of the Modern Periodic Table
2
Jigsaw lesson

• Slides
• Group A- Dobereiner Newland 3 -15
• Group B Mendeleev 16-24
• Group C Moseley 25-30
• Group DGeography 31-44

3
Periodic

• Means repeated in a pattern.
• The calendar is a periodic table of days.

4
(No Transcript)
5
(No Transcript)
6

• Halleys comet repeats periodically every 26
  years
• The seasons repeat each year.

7
During the nineteenth century, chemists began to
categorize the elements according to similarities
in their physical and chemical properties. The
end result of these studies was our modern
periodic table.
8
Johann Dobereiner
In 1829, he classified some elements into groups
of three, which he called triads.The elements in
a triad had similar chemical properties and
orderly physical properties.
(ex. Cl, Br, I and Ca, Sr, Ba)
Model of triads
1780 - 1849
9
Johan Dobereiner

• The Triad Model
• A German scientist, Johan Dobereiner
  (1780-1849), tried to classify elements into
• smaller and simpler subgroups. In 1829, he
  observed that elements with similar
• physical and chemical properties fall into groups
  of three. He called these related
• groups of three elements triads.
• One of these triads included chlorine, bromine,
  and iodine another consisted of
• calcium, strontium, and barium. In each of these
  triads, the atomic weight of the
• intermediate element is approximately the average
  of the atomic weights of the
• other two elements. The density of that element
  is approximately the average of
• the densities of the other two elements.
• The problem with this arrangement was that
  Dobereiners model became outdated
• as new elements were identified. A good model is
  able to incorporate newly
• understood information. Dobereiners Triad Model
  was not useful, since several
• newly discovered elements did not fit into it.

10
John Newlands
In 1863, he suggested that elements be arranged
in octaves because he noticed (after arranging
the elements in order of increasing atomic mass)
that certain properties repeated every 8th
element.
Law of Octaves
1838 - 1898
11
John Newlands
His law of octaves failed beyond the element
calcium.
WHY?
Would his law of octaves work today with the
first 20 elements?
1838 - 1898
Law of Octaves
12
Newlands

• Somewhat later, about 1864, a chemist by the name
  of Newlands came up with what he called the law
  of octaves. This idea was a bit more developed
  than Döbereiner's triads. Newlands arranged the
  known elements by atomic weights. In doing so, he
  noticed some recurring patterns, and the patterns
  were such that if he broke up his list of
  elements into groups of seven (starting a new row
  with the eighth element), the first element in
  each of those groups were similar to one another.
  So was the second element in each group and the
  third and so on. There was a certain pattern in
  the properties of elements that became even more
  apparent as time went on.

13
Newlands' Octaves
14
Newland

• However, there were some deficiencies in
  Newlands proposed arrangement. Several known
  elements did not fit his pattern. Newlands did
  not allow for the possibility of the discovery of
  additional elements at a later date. Further, he
  did not question whether all the atomic masses
  known to that date were correct. Newlands Law of
  Octaves was not a good model for explaining the
  relationship among the elements.

15
Links

• http//dl.clackamas.cc.or.us/ch104-07/newlands.htm
  
• http//www.genesismission.org/educate/scimodule/co
  smic/explore_1ST.pdf

16
Dmitri Mendeleev
In 1869 he published a table of the elements
organized by increasing atomic mass.
1834 - 1907
17
Organized Data

• Atomic Mass
• Density
• Color
• Melting Point
• Valence Number

18
Arranging Cards

• Increasing atomic mass
• Valence patterns repeated
• Fell into columns
• Columns had same valence and showed similar
  physical and chemical properties.

19

Mendeleev...

• was so confident in his table that he used it to
  predict the physical properties of three elements
  that were yet unknown.

20
He predicted elements that would be discovered.
He called two of them eka-aluminum and
eka-silicon. Mendeleevs predictions for Sc, Ga,
and Ge were amazingly close to the actual values,
his table was generally accepted.
21
Mendeleev in his own words

• In conclusion, I consider it advisable to
  recapitulate the results of the above work.
• 1. Elements arranged according to the size of
  their atomic weights show clear periodic
  properties.
• 2. Elements which are similar in chemical
  function either have atomic weights which lie
  close together (like Pt, Ir, Os) or show a
  uniform increase in atomic weight (like K, Rb,
  Cs). The uniformity of such an increase in the
  different groups is taken from previous work. In
  such comparisons, however, the workers did not
  make use of the conclusions of Gerhardt,
  Regnault, Cannizzaro, and others who established
  the true value of the atomic weights of the
  elements.
• 3. Comparisons of the elements or their groups in
  terms of size of their atomic weights establish
  their so-called "atomicity" and, to some extent,
  differences in chemical character, a fact which
  is clearly evident in the group Li, Be, B, C, N,
  0, F, and is repeated in the other groups.
• 4. The simple bodies which are most widely
  distributed in nature have small atomic weights,
  and all the elements which have small atomic
  weights are characterized by the specificity of
  their properties. They are therefore the typical
  elements. Hydrogen, as the lightest element, is
  in justice chosen as typical of itself.
• 5. The size of the atomic weight determines the
  character of the element, just as the size of the
  molecule determines the properties of the complex
  body, and so, when we study compounds, we should
  consider not only the properties and amounts of
  the elements, not only the reactions, but also
  the weight of the atoms. Thus, for example,
  compounds of S and Te, Cl and I, etc., although
  showing resemblances, also very clearly show
  differences.
• 6. We should still expect to discover many
  unknown simple bodies for example, those similar
  to Al and Si, elements with atomic weights of 65
  to 75.

22
Mendeleev

• Mendeleev realised that he had discovered, rather
  than designed, the periodic table is shown by his
  attitude towards it. First, he left gaps in it
  for missing elements. Leaving such gaps in tables
  of elements was not in itself new, but Mendeleev
  was so sure of himself that he was prepared to
  predict the physical and chemical properties of
  these undiscovered elements. His most notable
  successes were with eka aluminium ( Gallium) and
  eka-silicon ( germanium). Lecoq de Boisbaudran
  discovered gallium in 1875 and reported its
  density as 4.7g cm -3, which did not agree with
  Mendeleevs prediction of 5.9g cm -3. When he was
  told that his new element was Mendeleevs
  eka-aluminium, and had most of its properties
  foretold accurately, Boisbaudran redetermined its
  density more accurately and found it to be as
  predicted, 5.956 g cm -3. There could be no doubt
  now that Mendeleev had discovered a fundamental
  pattern of Nature.

23
Mendeleev in his own handwriting.
24
Mendeleev links

• http//www.chemsoc.org/viselements/pages/history_i
  ii.html

25
Henry Moseley

• Ordered elements by atomic number instead of
  atomic mass.
• First to determine the atomic numbers of the
  elements.
• Killed during battle of Gallipoli at the age of
  27.

26
Moseley, Henry

• Moseley, Henry (1887-1915) A British chemist who
  studied under Rutherford and brilliantly
  developed the application of X-ray spectra to
  study atomic structure his discoveries resulted
  in a more accurate positioning of elements in the
  Periodic Table by closer determination of atomic
  numbers. Tragically for the development of
  science, Moseley was killed in action at
  Gallipoli in 1915.
• In 1913, almost fifty years after Mendeleev,
  Henry Moseley published the results of his
  measurements of the wavelengths of the X-ray
  spectral lines of a number of elements which
  showed that the ordering of the wavelengths of
  the X-ray emissions of the elements coincided
  with the ordering of the elements by atomic
  number. With the discovery of isotopes of the
  elements, it became apparent that atomic weight
  was not the significant player in the periodic
  law as Mendeleev, Meyers and others had proposed,
  but rather, the properties of the elements varied
  periodically with atomic number.
• When atoms were arranged according to increasing
  atomic number, the few problems with Mendeleev's
  periodic table had disappeared. Because of
  Moseley's work, the modern periodic table is
  based on the atomic numbers of the elements.

27
Henry Moseley

• Henry Moseley was an English physicist born in
  1887. As a student working for Rutherford at the
  University of Manchester, Moseley determined that
  elements fell into a precise order on Mendeleev's
  period table. By studying the x-rays emitted by
  certain consecutive elements, under specific
  conditions, he concluded that the positive charge
  of an atom had characteristic values. "By
  photographing the x-ray spectrum of 12 elements,
  10 of which occupied consecutive places on the
  periodic table, he discovered that frequency of
  the K-lines in the spectrum of each element was
  directly proportionate to the squares of the
  integer representing the position of each
  successive element in the table." He said "there
  is a fundamental quality, which increases by
  regular steps as we pass from one element to the
  next." (1) This he called the Atomic Number.
• Moseley was killed by a sniper in 1915 while
  serving in the British army in World War I.

28
Modern Periodic Table

• Based on Moseleys worknot Mendeleev
• Based on atomic number not atomic weight.
• The atomic number increases from left to right.
• The Periodic Law - the physical and chemical
  properties of the elements are periodic functions
  of their atomic numbers.

29
Modern Periodic Table

• Contains 115 elements
• 92 are naturally occurring (found on Earth)
• Other elements are made in laboratories.
• All elements with higher atomic numbers than
  Uranium are radioactive.

30
Elements w/ 3 letter symbols i.e.. Uun or Uuu or
Uub have not been given official names since they
are so new.
31
Periodic Table Geography
32
The horizontal rows of the periodic table are
called PERIODS.
33
The elements in any group of the periodic table
have similar physical and chemical properties!
The vertical columns of the periodic table are
called GROUPS, or FAMILIES.
34
Group (Family)

• The 18 Columns Have similar properties.
• For example, Li, Na, and K are all soft, white,
  shiny metals and are highly reactive.

35
Alkali Metals
36
Alkaline Earth Metals
37
Transition Metals
38
InnerTransition Metals
These elements are also called the rare-earth
elements.
39
Halogens
40
Noble Gases
41
Metals, Nonmetals, and Metalloids
42
Characteristics of Metallic Elements

• Metals have a shiny metallic luster.
• Metals conduct heat well and conduct electric
  currents in the solid form.
• Metals are malleable.
• For example, gold, Au, can be hammered into very
  thin sheets without breaking.
• At 20?C, all metals are solids except mercury,
  which is a liquid.

43
Characteristics of Nonmetal Elements

• Nonmetals are dull.
• Nonmetals do not conduct heat well and do not
  conduct electric currents.
• Nonmetals are brittle.
• At 20?C, some nonmetals are solids, some are
  gasses, one is a liquid.

44
Characteristics of Metalloids Elements

• Metalloids have characteristics of both metals
  and nonmetals.
• Metalloids often have a shiny metal luster
• Metalloids are often brittle solids.
• Metalloids will conduct electricity a little and
  are called semiconductors. They are used in
  computers.

45
The periodic table is the most important tool in
the chemists toolbox!
46
Homework Due____

• P114 1-10